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[1] "Pesc record - ieee power electronics specialists conference," 1992, pp. 2 vol. xxxv+1450. The following topics are dealt with: soft-switched and resonant power converters; induction motor drive technology; power converter technology; induction motor control; inverter technology; transportation applications; utility power conversion: modulation and spectra: DC/DC power converters; power conversion for photovoltaic power systems resonant power converter analysis and control; switched reluctance motor drives; brushless DC motor drives; power factor improvement regulators; space power systems; magnetics, modeling and simulation; magnetics, structures and applications; high power conversion techniques; and distributed power supplies for computer and communications [2] A. Ackva, H. Reinold, and R. Olesinski, "A simple and self-adapting high-performance current control scheme for three phase voltage source inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 435. An adaptive optimized regulator (AOR) for three-phase voltage source inverters is presented. The zero-voltage vectors are used systematically to reduce the switching frequency and can be reached by switching only one inverter leg. In the steady stage the controller applies to the machine only those three voltage vectors which are directly adjacent to the machine voltage (similar to pulse width modulation). Adaptive identification of position and amplitude of the determining machine voltage vector is realized by multilevel hysteresis comparators and a switching table. The dynamic performance is as excellent as for the three-phase bang-bang controller, and the hardware implementation is very simple [3] A. K. Adnanes, R. Nilssen, and R. O. Rad, "Power feed-back during controller failure in inverter fed permanent magnet synchronous motor drives with flux weakening," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 958. When permanent magnet synchronous motors are operated in the flux weakening region, the internal voltage can be much larger than the DC link voltage. If the switching signals are blocked, the freewheeling diodes act as a rectifier, and the motor will feed power back into the inverter. The magnitude of the feedback power during such controller failure is investigated. Simulations and approximate analyses are used to obtain descriptive and comparative curves. Measurements verify the computer results but also show that nonlinear effects could have significant influence [4] V. G. Agelidis, P. Ziogas, and G. Joos, "`dead-band' pwm switching patterns," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 427. It is pointed out that continuity has been assumed to be a necessary condition for the implementation of switching patterns for pulse-width-modulated (PWM) converters. This is probably based on the intuitive feeling that switching pattern discontinuities dead-band-degrade the quality of output/input voltage/current waveforms by introducing low-order harmonics. The authors challenge this notion by showing that discontinuous switching patterns for PWM converters can yield better performance than their continuous counterparts. Performance is defined as harmonic distortion normalized with respect to switching frequency, and serves as a measure of comparison with continuous PWM techniques. The applications considered include general-purpose and application-specific solid-state power supplies utilizing voltage current inverters and PWM synchronous or buck-type rectifiers. Theoretical considerations are verified on an experimental unit [5] M. Alakula, B. Peterson, and J. Valis, "Damping of oscillations in induction machines," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 133. A method for damping the oscillations in induction machines, independent of what is exciting them, is proposed and verified. It is shown that, if the stator flux is controlled, the machine appears as if the stator resistance is zero, whereby the damping of the parallel resonance is increased to infinity. It is also shown that, if the torque-producing stator current component is negatively fed back to the stator frequency reference, the stator resistance from the series resonant point of view can be given any value, whereby the damping of the series resonance is variable. To verify the function of the control system described, a series of measurements has been made on a 1.5 kW, four-pole induction motor [6] B. Alberdi, C. Lucia, R. Martin, and A. Lopez, "Design and construction of an rf power supply at 100 kv, 30 a dc output using solid-state dc-dc converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1111. A power supply design for RF equipment using high-frequency commutation technology, which is totally solid state and without energy storage at the output filter or protection crowbar, is presented. The 3 MW, 100 kV, 30 A power supply offers the low ripple, excellent dynamic and static stability, and very fast turnoff (better than 5 μs) required by RF equipment [7] S. M. Al-Kasimi and A. O. BaQubas, "The inductance analysis of the trapezoidally railed linear synchronous motor as compared to the zig-zag version for maglev applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1447. The trapezoidally railed linear synchronous motor provides a combined lift and thrust for Maglev vehicles. Its magnet is U-shaped with split poles surrounded by inverter-fed coils distorting field among the four. Modified from zig-zag, its rail is trapezoidal and will propel to minimize reluctance. This paper obtains in theory the inductance of the new version compared to the old one for inverter design [8] B. Allard, H. Morel, and J. P. Chante, "State-variable modeling of high-level injection regions in power devices-application to power system simulation," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 885. Modeling procedures that allow accurate simulations of power systems and predictions of electrical constraints endured by power devices are presented. Bond graph theory leads to a device modular analysis, and internal approximation allow state variable modeling of the high-level injection semiconductor layers. Applying these methods to the high-voltage power bipolar transistor gives good primary simulation results [9] A. V. Anunciada and M. M. Silva, "On the stability and subharmonic susceptibility of current-mode controlled converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 345. The authors present stability conditions for constant switching frequency power converters with current-mode control. The conditions take fully into account the interaction of the current and voltage feedback loops, and give explicit limits for the loop gains as a function of the duty ratio and the slope of the compensation ramp. The conditions are confirmed by experiment, and it is shown that they provide more stringent limits than the conventional stability analysis. The authors also introduce the concept of subharmonic susceptibility, which is closely related to the stability conditions. This is a useful design parameter which provides a measure of the degree of stability [10] J. Arau, Q. Jimenez, J. Uceda, and J. Sebastian, "Improving large signal analysis in dc/dc converters with a modified small signal model," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 512. Starting from large signal considerations, the authors introduce a modified small signal model to make a critical evaluation of the pulsed load operation of the basic DC/DC converters. The necessary constraints which permit the use of the proposed model with acceptable accuracy in typical large signal operation are explored. It is confirmed that the modified small signal model proposed here is able to predict DC/DC dynamical behavior if global large signal stability criteria are first achieved, and that it can measure the prediction error in accordance with the converter characteristic studied. These conclusions indicate that more traditional and complex feedback networks can be incorporated in a simple way [11] J. A. Asumadu and R. G. Hoft, "New algorithms for generation of notches in pwm waveforms using linear block codes," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 465. The authors describe a method for the elimination of harmonics in pulse-width-modulation (PWM) waveforms using the algebra of linear block digital codes which substitutes harmonic generator polynomials, with zero and unity coefficients, for the nonlinear equations required in Fourier series harmonic elimination. The method shows that a single polynomial can be defined to eliminate a very large set of harmonics. Transcendental equations obtained in PWM waveform harmonic elimination using Fourier series of linear algebraic equations using Walsh series are replaced by linear block codes. One generator vector may cancel unwanted harmonics. The software is very simple; memory requirements are greatly reduced; and advances in microprocessor technology and speed make this mmm most advantageous for harmonic elimination in real-time systems [12] A. Bado, S. Bolognani, and M. Zigliotto, "Effective estimation of speed and rotor position of a pm synchronous motor drive by a kalman filtering technique," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 951. The estimation of the speed and the rotor position of a permanent magnet synchronous motor drive by means of a stochastic filtering technique is considered. The proposed estimation algorithm does not require knowledge of the mechanical parameters and initial rotor position, thus overcoming two of the biggest drawbacks of the speed and position estimation systems already developed. In addition, the estimation algorithm is merged with a predictive algorithm for the control of the motor currents. The two algorithms share some routines, which reduces the computational burden [13] A. Balakrishnan, W. D. Palmer, W. T. Joines, and T. G. Wilson, "Inductance of planar rectangular-spiral strip conductors for low-profile inductors," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1401. Two methods are presented for calculating the inductance of planar rectangular spirals. The first method assumes current flows only in the exact center of the conductor. The second method is based on uniform current distribution across the conductor width, and results in significant improvements in the calculated value of the inductance. The effect of introducing a magnetic core is also studied. The calculated values of inductance from both methods are compared with laboratory measurements, and the accuracy of the methods is demonstrated [14] G. Bezanov and J. Richardson, "Algorithmic modelling of pwm solution sets for online control of inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 595. It is demonstrated that by using accurate modeling techniques it is possible to define an analytic expression describing the law governing the commutation angles of an optimal pulse width modulation (PWM) strategy. The read-only-memory (ROM)-based approach is avoided by describing the law governing the switching angles of the harmonic elimination strategy by an analytical expression which is executable in real time. This expression is derived from accurate modeling of offline-prepared switching patterns, which provides for the elimination of the 5 th, 7 th, 11 th, and 13 th harmonics with control of the fundamental voltage component. A digital implementation method is described whereby three-phase generated PWM waveforms are obtained. Emphasis is placed on the quality of harmonic elimination and the speed of online execution of the pulse-width generation routines. The system allows for a wide operating frequency range without any modification to the hardware. The flexibility of the software controller is demonstrated [15] V. B. Bhavaraju and P. Enjeti, "Analysis and design of an active power filter for balancing unbalanced loads," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1214. An active power filter is proposed for balancing unbalanced loads. A three-phase, PWM AC-to-DC converter topology with inductive energy storage is controlled to continuously inject desired negative sequence currents into the system to achieve balancing of continuously varying unbalanced loads. The principle of operation is as follows: the negative sequence components of the load currents are measured in magnitude and in phase and the PWM-controlled active power filter is controlled to inject currents opposite to these quantities, thereby achieving the balancing function. The operation of the proposed system and the selection of the active power filter components are discussed in detail. Experimental filter operation is verified for an unbalanced load [16] R. Bhide and S. R. Bhat, "Modular power conditioning unit for photovoltaic applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 708. The concept of modular power conditioning systems for photovoltaic (PV) applications is discussed, with particular reference to the battery as the load. A MOSFET-based power conditioning unit (PCU) of 1 kW capacity is discussed in detail along with a control algorithm to track the maximum power point. Maximum power from each PV array is extracted in spite of any mismatch in the array characteristics. One system controller is capable of handling several PCUs, simplifying the design and resulting in a lower cost of the system. It was observed that the maximum power point tracking (MPPT) increases the power output by abut 10% over a day as compared to the direct connection [17] F. Blaabjerg and J. K. Pedersen, "An optimum drive and clamp circuit design with controlled switching for a snubberless pwm-vsi-igbt inverter leg," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 289. A drive circuit for an insulated gate bipolar transistor (IGBT) with overcurrent protection and controlled switching has been optimized together with a normal passive clamp in an effort to achieve a robust and reliable snubberless inverter leg. Expressions for the design of the snubberless concept including drive circuit and clamp are given. Measurements show a good agreement with the design expressions. A short-circuit test at different operating temperatures is also performed as well as multiple short-circuits. It is concluded that the drive circuit and the nonactive clamp are a reliable and cheap solution for protecting the inverter leg [18] B. K. Bose, "Power electronics and motion control-technology status and recent trends," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 3. The author reviews the technology status and trends in power electronics and motion control with emphasis on AC machine drives. A comprehensive review of power semiconductor devices, power converter circuits, machine drives, and various motion control techniques is included. The impact of expert systems, fuzzy logic and neural networks in intelligent motion control is discussed [19] K. C. Burgers, J. D. van Wyk, and M. J. Case, "A high performance induction motor drive system based on a non-linear resonant pole soft switching inverter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 111. A novel nonlinear resonant pole soft switching inverter is used to drive a 4 kW three-phase induction motor in a high-performance drive system. The switching elements are insulated-gate bipolar transistor (IGBT) power modules rated at 25 A, 1000 V. Device voltage stresses are of the order of 1 p.u. The peak current stresses are as low as 1.3 p.u. A sliding-mode stator flux field orientation scheme based on direct self control is chosen as the motor control scheme. The overall control is carried out using a T800 transputer system programmed in OCCAM [20] V. A. Caliskan, R. Liu, and C. Q. Lee, "Ac analysis of dc/dc resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 354. The authors introduce some extensions to R.L. Steigenwald's (1988) classical AC analysis of resonant DC/DC power converters. These include applications to third-order systems and one class of zero voltage switching (ZVS) converters. Based on analog filter theory, one can explain why the third-order counterparts of the series resonant converter and parallel resonant converter possess improved characteristics. Gain sensitivity is introduced as a performance index for comparing performance characteristic features. It is shown that at least one other class of ZVS converter can be analyzed by using an extension to this approach [21] A. Campos, G. Joos, P. Ziogas, and J. Lindsay, "Analysis and design of a series voltage unbalance compensator based on a three-phase vsi operating with unbalanced switching functions," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1221. A series voltage compensator for three-phase unbalanced sources is presented and analyzed. The system, based on a three-phase voltage source inverter connected in series to the supply through a three-phase delta-wye power transformer, proves to be feasible and performs as expected. A 1.3 kVA prototype was built and tested with 10.75% of unbalance and 9.01% of magnitude error (|<i>MF</i>|=0.909). The results showed a very good correlation with the expected performance, producing a balanced line-to-line load voltage with a low harmonic content (average THD=20%), without filter. The compensator required only 168.8 VA, which shows one of the main advantages of the compensator scheme proposed [22] G. A. Capolino and H. Henao, "Discrete implementation for regulators in indirect vector-controlled induction machine drive," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 672. The authors present a comprehensive method to compute the parameters of an antiwindup proportional-plus-integral (PI) torque regulator for an indirect vector-controlled induction machine drive. Starting from the classical scheme with quasi-independent flux and torque control loops, a second-order transfer function is derived for torque control from a bounded current. Then, using an antiwindup PI regulator, a pole placement method is given to provide the two parameters. The influence of discretization is also investigated and tested on an experimental direct-digitally-controlled device [23] F. Caricchi, F. Crescimbini, T. A. Lipo, and E. Santini, "Innovative inverter topology for concentrated winding pm motor drives," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 964. Applications of concentrated winding machines prompt new solutions in designing the power converter which supplies the machine, since the machine average torque can be increased significantly by supplying three-phase current waveforms matching in full the trapezoidal back EMF. However, such current supply arrangements involve a third-harmonic current flowing into the machine. An innovative converter topology is presented to overcome this problem. This new configuration extends the standard layout of conventional PWM voltage source inverters by adding a fourth branch devoted to controlling the machine neutral voltage. Computer simulations are used to show the inverter modes of operation. Experimental results for a converter prototype which has been constructed using IGBTs are reported [24] J. M. Carrasco, F. Gordillo, L. G. Franquelo, and F. R. Rubio, "Control of resonant converters using the lqg/ltr method," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 814. A method of controlling resonant converters based on optimal techniques and the study of the robustness is proposed. The method is more systematic than the previous one using classical methods, and the rules for changing the parameters to achieve the aims are clear. With this method it is easier to achieve better performances. The electronic implementation of this controller is easy, being based on several operational amplifiers. Although the proposed controller has been applied to a specific converter, the design can be easily generalized to any kind of resonant converter [25] V. Cascone, M. Galasso, L. Mantica, and M. Oberti, "Design of active filters for dynamic damping of harmonic currents generated by asynchronous drives in modern high power locomotives," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 404. In order to reduce the harmonic contents of the currents injected in an overhead traction line while minimizing the electromagnetic interference with the signaling system, the use of an active filter seems to give marked advantages. The authors analyze a reliable active filter design, applied to a high-power, high-speed locomotive. The configuration, mainly derived from existing applications of harmonic power filters for industrial plants, was simulated and investigated, especially from the viewpoint of the dynamic behavior [26] E. Cerruto, A. E. Consoli, A. Raciti, and A. Testa, "A simple and robust adaptive controller for pm motor robotic drives," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 973. The theoretical development and the practical implementation of an adaptive speed and position regulator suitable for robotic applications are addressed. The proposed adaptive control scheme, which is characterized by a reduced amount of computation, is based on the model reference adaptive control approach, and employs a disturbance torque observer that makes it possible to noticeably simplify the adaptive algorithm. Simulations that compare the proposed control scheme with standard speed and position regulators are reported. Experimental results for a prototype based on a commercial PC board, used to evaluate the features of the proposed adaptive control scheme are also reported [27] D. K. W. Cheng and K. L. Ng, "A new approach in switching mode transformer design with distributive configuration," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1387. A switching mode transformer design approach with distributive configuration is devised. This configuration of cores offers inherent characteristics of even thermal distribution and extremely low profile construction. An approximate leakage inductance formula is derived from the magnetic field intensity. Various winding constructions are evaluated in order to find the optimized configuration with the lowest leakage inductance and the best coupling coefficient. A SPICE transformer model using the inductance matrix and T-model technique is also discussed. A power supply prototype was built to verify its performance [28] K. W. E. Cheng and P. D. Evans, "Optimisation of high frequency inductor design of series resonant converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1416. An analytical solution for the eddy current losses in a high frequency power inductor is obtained in a generalized way for single and multistrand conductors. The design optimization for toroidal inductors, using stranded conductors on a low permeability core, is then undertaken. Core loss and DC and AC copper losses are taken into account. The goal is to minimize weight and cost for known thermal conditions. Alternatively, the incremental weight loss characteristics generated provide additional design information for space use when total system weight is critical. The calculated figures of 60 g of additional inductor weight per watt of loss saved can be used as part of an overall system optimization procedure [29] N. S. Choi, Y. C. Jung, H. L. Liu, and G. H. Cho, "A high voltage large capacity dynamic var compensator using multilevel voltage source inverter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 538. A multilevel pulse-width-modulation (PWM) voltage-source inverter is connected to a static volt-ampere-reactive (VAr) compensator (SVC) as a large-scale power source. The SVC can be directly connected to AC mains of 6600 V, allowing full utilization of semiconductor devices like gate turn-off thyristors (GTOs). The voltage balancing condition of the DC slide capacitors is identified based on the fundamental circuit modeling of the inverter, and a five-level PWM is used to meet the condition. Owing to the multilevel approach, a low distortion in the input currents results and filter size thus is minimized. To confirm the validity of the fundamental circuit modeling of the SVC system with a five-level inverter, the system was simulated using commercial simulation packages [30] J. L. Christian, Jr., J. E. Dickman, R. W. Bercaw, I. T. Myers, A. N. Hammoud, M. Stavnes, and J. Evans, "Wiring for aerospace applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1133. The authors summarize the state of knowledge of arc propagation in aerospace power wiring and efforts by the National Aeronautics and Space Administration (NASA) toward the understanding of arc tracking phenomena in the space environment. Recommendations are made for additional testing. A database of the performance of commonly used insulating materials will be developed to support the design of advanced high power missions, such as Space Station Freedom and lunar/Mars exploration [31] J. C. Clare, P. R. Mayes, and W. F. Ray, "Bidirectional power convertor for voltage fed inverter machine drives," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 189. The authors describe the development and operational characteristics of a prototype bidirectional AC-DC power converter based on a novel topology, suitable for feeding the DC link of voltage-fed inverter drives. The circuit uses fewer components than proposed alternatives and exhibits significantly less supply current distortion than the conventional capacitively smoothed rectifier circuit. Experimental results showing operation in the monitoring mode, in the regenerating mode and during mode changeover are given, confirming the feasibility of the proposed circuit [32] J. A. Cobos, J. Sebastian, J. Uceda, E. de la Cruz, and J. M. Gras, "Study of the applicability of self-driven synchronous rectification to resonant topologies," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 933. Synchronous rectification techniques applied to high-frequency resonant topologies are studied. The on-resistance reduction of the MOSFET synchronous rectifier produces an increase of the parasitic capacitances. A selection of the resonant topologies where these capacitances are absorbed by the resonant tank, allowing self-driving of the synchronous rectifier, is presented. High efficiency has been obtained in a low-output-voltage (5 V and 3.3 V) forward ZVS-MRC with resonant synchronous rectification. Layout effects appeared to be very important at high switching frequencies. Even better results are expected in a hybrid prototype using specific low gate resistance MOSFETs as synchronous rectifiers [33] Z. Cucej, J. Mohorko, P. Planinsic, K. Jezernik, and D. Donlagic, "Vector control method in sliding mode control of an ac motor," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 253. The direct Lyapunov method was used to determine the sliding-mode condition for a vector control variable structure system. This sliding condition enables the use of optimization criteria for selecting the inverter output voltages. A description of the optimization procedure which results in three switching strategies of the inverter that feeds the AC motor is included. The selection of the output voltage for the optimal selected strategy is derived. A problem regarding the definition of reference control quantities is pointed out. The experimental implementation of the proposed control is described, and simulation results are given [34] F. G. de Beer, W. Deleroi, and J. B. Klaasens, "Efficiency improvement of a sliding-mode controlled induction motor by flux removal," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 145. A method to calculate a trajectory for the rotor flux is presented. This trajectory corresponds to an electromagnetic transition of the induction motor which links without any discontinuities, or electromagnetic transients, to the preceding and the succeeding steady state of the motor. The way the trajectory is presented differs from the known field-oriented control, but the result can be translated into the field-oriented <i>d</i>- and <i>q</i>-components of the stator current. Cost functions are derived to calculate the optimal shape of the rotor flux trajectory to achieve the lowest power peak. The shape of the trajectory is calculated for the sliding-mode positon drive. An experimental induction motor position drive was built using the sliding mode control technique. The sliding mode is equipped with a band around the sliding line for which the torque and rotor flux are zero. When the rotor axis moves inside this band, all electrical power, copper, and iron losses are avoided. During the experiments, an energy loss of 42% resulted as compared with the standard sliding-mode control [35] L. C. de Freitas, J. B. Vieira, Jr., V. J. Farias, H. L. Hey, P. S. Caparelli, and D. F. de Cruz, "An optimum zvs-pwm dc-to-dc converter family: Analysis, simulation and experimental results," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 229. The authors consider a family of DC-to-DC power converters using the lossless commutation pulse-width-modulation (PWM) source feeding resonant disconnecting circuit cell with resonant cycle interruption (LC-PWM-SF-RDC) to overcome the problems present in quasi-resonant converters (QRCs) and QRCs-PWM. The most important property of this family of devices is the ability to regulate output power and voltage by PWM, with constant operating frequency, without load limitation, and without sacrificing the lossless commutation. The authors present the operating principle and design-oriented analysis, output characteristics, relevant equations, and simulation results. These procedures are validated by a prototype laboratory implementation [36] A. de Hoz and E. de la Cruz, "Analysis and design of a zero current switched quasi-resonant converter with synchronous rectification for low output voltage applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 221. An analysis of a zero-current-switched quasi-resonant power converter (ZCS-QRC) including the effects of a finite magnetizing inductance is presented. The resulting topology seems to be very useful for the implementation of synchronous rectification techniques in a nondissipative way, allowing high-frequency operation. A design guideline based on the design procedure developed is given. Simulation and experimental results show very good performance in terms of high efficiency for low output voltage and high output current applications. Experimental results for two different output conditions (5 V/20 A and 3.3 V/20 A) are presented. Both converters work at a nominal switching frequency of 250 kHz, achieving a very good trade-off between efficiency and size [37] E. de la Cruz, S. Ollero, J. A. Cobos, J. Uceda, J. M. Lopera, and F. Nuno, "Performance comparison of four practical implementations based on pwm, quasi and multiresonant topologies for on board dc/dc converters in distributed power architectures," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 917. In distributed power system architectures, the DC/DC conversion stage turns out to be an onboard converter with very stringent specifications, particularly in terms of efficiency and size. Practical implementations of four DC/DC converters based on PWM, quasi-resonant, and multiresonant topologies are compared for a telecommunications onboard application. Experimental results concerning efficiency, component stresses, EMC behavior and size are provided, and a comparative analysis based on these data is performed [38] J. R. de Villiers, J. D. van Wyk, and J. A. Ferreira, "Study of a generic topology for a double nonlinear resonant pole converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 633. The advantages that can be achieved by using nonlinear capacitors in nonlinear resonant pole converters are shown. The double nonlinear resonant pole converter exhibits lower switching losses, reduced parasitic oscillations, and lower overrating of the switching devices. These advantages can be obtained by merely changing two existing linear capacitors for nonlinear capacitors. This should not increase the cost of the inverter, nor will any additional or different control schemes be needed. The advantages of the double nonlinear resonant pole phase arm increase with the increase in the nonlinearity coefficient of the capacitors [39] J. A. Donahue and A. M. Neech, "A 17 kw series-resonant converter for a co<sub>2</sub> laser gas discharge load," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1116. A system comprising a combination of 17 kW series-resonant DC-DC converters is used to power a CO<sub>2</sub> laser gas-discharge load in both pulsed and continuous modes. The converters use ASCRs for switching at up to 16.7 kHz with natural commutation yielding a simple topology. Commutation problems encountered are discussed, and a solution is presented. A multiloop control system allowing programmable pulse-shaping with a leading-edge current boost of over 5 to 1 and linear control of pulse-plateau current is described [40] J. L. Duarte, J. Rozenboom, T. Peijnenburg, and H. Kemkens, "Simulating a bjt-mosfet cascode-connected power switch suitable for resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 893. A cascode connection of a high-voltage bipolar transistor and a low-voltage MOSFET is modeled and simulated using PC-based SPICE software. A simple representation for the reverse recovery phenomena in the bipolar power transistor, which compensates the incompleteness of the PSPICE model is described. The effect of ferromagnetic hysteresis in the base drive transformer has been taken into account. Comparison of simulations with experimental results is provided. The use of this combinational switch is demonstrated in a 30 W class-E inverter breadboard operating at 270 kHz from a DC input voltage up to 310 V. The switch is capable of holding off voltages beyond 1500 V [41] W. G. Dunford, L. Welder, and P. R. B. Ward, "The production of impulsive torques in a photovoltaic powered pumping system," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 719. Methods of providing the high starting torque required in photovoltaic-powered progressive-cavity type pumping systems are discussed. It is shown that suitable impulsive torques can be obtained by using a reservoir capacity. The sizing of this capacitor is discussed in detail for a permanent magnet DC drive, and experimental verification is provided. It is shown that electromagnetic torque pulses in a photovoltaic powered DC drive can be satisfactorily predicted. For a specified armature resistance the peak value is proportional to the initial input voltage. The value of capacitance representing critical damping (4<i>L</i>/<i>R</i>) may be viewed as an optimum choice in terms of peak current/microfarad [42] M. A. Dzieniakowski and M. P. Kazmierkowski, "Microprocessor-based novel current regulator for vsi-pwm inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 459. A simple microprocessor-based current regulator for pulse-width-modulated (PWM) transistor inverters is presented. The control strategy is based on the discrete delta modulation principle. The originality of the technique resides in the sampling method used for the delta-modulation-based current regulator. The design of the system with application of an SAB80C535 one-board microprocessor controller is discussed. Simulation and laboratory tests results showing the properties of the current regulator are presented [43] C. Elmas and H. Zelaya De La Parra, "A dsp controlled switched reluctance drive system for wide range of operating speeds," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 844. The authors describe a practical implementation of a switched reluctance drive (SRD) for a wide range of operating speeds, taking advantage of both current and voltage-controlled configurations. The design uses a modern DSP (TMS320C30), allowing great flexibility for various real time applications. The results are compared with those based on the modeling of the SRD, giving an indication of the interesting characteristics of the switched reluctance motor for the two basic configurations and the possibility of implementing more sophisticated control strategies [44] H. Endo, T. Yamashita, and T. Sugiura, "A high-power-factor buck converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1071. A high-power-factor buck converter is proposed. The converter is composed of rectifier diodes, a small input capacitor, and a buck converter. It supplies low output voltages and uses low voltage semiconductor devices and ceramic capacitors. Two operation modes exist in the converter: discontinuous and continuous inductor current modes. Analysis and experimentation show that the converter's power factor is over 0.9 in discontinuous mode by constant duty ratio operation. It is clarified that the power factor decreases to about 0.7 in continuous mode by constant duty ratio operation, and it can be improved to over 0.9 by a new input current control system [45] R. Farrington, M. M. Jovanovic, and F. C. Lee, "Analysis of reactive power in resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 197. A number of resonant power converters are analyzed to derive the reactive power and RMS current circulating through the transformer. The results of the analysis are used to define design guidelines that minimize the circulating energy in the converters and maximize their efficiencies and power densities. The analyzed converter topologies include the half-bridge zero current switching quasi-resonant converter (HB ZCS-QRC), the half-bridge zero-voltage-switched multiresonant converter (HB ZVS-MRC), the constant-frequency half-bridge zero-voltage-switched multiresonant converter (CF HB ZVS-MRC), the HB ZVS that uses the magnetizing inductance as a resonant element (HB ZVS-MRC (<i>L</i><sub>M</sub>)), and the full-bridge series-parallel-resonant converter (FB SPRC). The results of the analysis show that the HB ZCS-QRC and the soft-switched HB ZVS-MRC (<i>L</i><sub>M</sub>) circulate relatively small amounts of power. However, the circulating power in the HB ZVS-MRC, CF HB ZVS-MRC, and SPRC is found to be considerably larger. The analysis is used to generate sets of characteristics for each converter that can be used in their design optimization based on the minimization of the circulating power [46] A. Ferrah, K. G. Bradley, and G. M. Asher, "Sensorless speed detection of inverter fed induction motors using rotor slot harmonics and fast fourier transform," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 279. A novel approach to sensorless speed detection for adjustable-speed AC drives is described. No a priori knowledge is required about the motor construction, electrical parameters, or load condition. In addition, no external tuning is needed for the system. The technique is based on instantaneous spectral estimation using the fast Fourier transform, whereby the speed-dependent slot ripple harmonic frequency is determined. For the assessment of this technique, an all-digital speed detector has been built around a general-purpose 386 microcomputer. The performance of this detector over a wide range of inverter frequencies and load conditions is discussed [47] J. A. Ferreira, W. A. Cronje, and W. A. Relihan, "Integration of high frequency current shunts in power electronic circuits," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1284. The principles that determine the high frequency behavior of current shunts are identified and applied to broaden the concept of shunt construction by viewing the shunt as an integrated part of the power electronic circuit. It is demonstrated that a shunt constructed from discrete components, like a number of resistors in parallel, can have bandwidth performance on a par with shunts constructed from foil. The prerequisite is that the layout and spatial orientation of the elements provide the correct field distributions. Such structures often permit easy integration as a permanent part of the power converter layout. A flat structure constructed in this way demonstrates the principles, which can readily be extended to more complex geometries. Some examples of such complex geometries are given in the form of a high-dissipation load impedance with the shunt as an integral part and a snubber inductance with a shunt integrated into its structure. The necessity for electromagnetic field analysis of the layout or component structure is demonstrated. Examples of integrated shunts are presented with analysis and experimental results [48] S. J. Finney, T. C. Green, and B. W. Williams, "Spectral characteristics of resonant link inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 607. The limitations on the operating frequency of hard-switched and resonant-link inverters are studied. The maximum operating frequency of a hard-switched inverter is found to be well defined by the allowed power dissipation and the switching losses. For resonant link inverters the upper limit is not so well defined and depends on a trade-off between a number of different factors. For a system using high-power bipolar transistors is it seen that a hard switched inverter is limited to switching frequencies of below 2 kHz, while a comparable resonant link inverter is restricted to frequencies below 20 kHz. The frequency spectrum of the resonant link configuration has been compared with pulse width modulation (PWM). It was shown that the improvement in harmonic distortion associated with a delta-modulated resonant link is not as great as could be expected from the increase in operating frequency that may be obtained. This is a result of constraints placed on switching instants and the need to use integral pulse modulation. The simulations presented show that high-frequency resonant link systems generate more low-frequency components than those using low-frequency PWM [49] M. Fracchia, T. Ghiara, M. Marchesoni, and M. Mazzucchelli, "Optimized modulation techniques for the generalized <i>n</i>-level converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1205. A balancing control strategy that allows the voltage differences among the DC link capacitors of the generalized <i>n</i>-level power converter to be minimized is presented. The case <i>n</i>=3 is treated, but the technique can be generalized to larger <i>n</i> values. The balancing algorithm does not achieve correct voltage sharing of the capacitors under all operating conditions, but it provides a great improvement. This strategy appears to be very promising in single-phase applications, for which nonredundant switching configurations do not affect the capacitor voltage balance [50] F. Franck and D. Schroder, "The influence of finite rated filter and energy-storage elements on the behaviour of multi-resonant single-cell converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 206. Finite-rate filter and energy storage elements are shown to have a large impact on the behavior of DC-DC power converters operating in the resonant mode. They change the operating area and define the low frequency characteristics. These effects are described together with their mathematical backgrounds. To optimize a resonant converter, e.g. to reduce the stresses and to improve the efficiency, the proper design of filter and energy storage components is also necessary, as well as the design of the resonant elements. As an example a zeo voltage switching multiresonant Cuk converter is investigated. It is shown that by shrinking the rating of the typical Cuk capacitor and by altering the winding ratios of the transformer and coupled inductor, the operating area will be improved [51] G. Gentile, N. Rotondale, and M. Tursini, "Investigation of inverter-fed induction motors under fault conditions," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 126. A mathematical model based on space-vector theory is used to analyze inverter-fed induction motors faults. Inverter supply faults like an open phase fault, the failure of a transistor to switch on, the delay in a branch command, or the stand of the branch command are analyzed. These events introduce an asymmetry in the supply voltages, in the current values, and in the spatial field distribution. A detailed investigation of typical inverter supply failures is presented and discussed in order to identify remedial strategies [52] L. Gerbaud, J. Bigeon, and G. Champenois, "Modular approach to describe electromechanical systems-using macsyma to generate global approach simulation software," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1189. The study of a complete electromechanical system is made easier by splitting it into several functional modules. However, for dynamic simulations, this approach may induce problems in solving system equations. The authors propose a tool, based on symbolic language, using modular descriptions for users, and automatically generating FORTRAN programs with a global approach, in a motor which solves differential equations [53] P. Gil, J. Sebastian, J. A. Cobos, J. Uceda, and F. Aldana, "Analysis of the zero-current-switched quasiresonant converters used as power factor preregulators," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1052. The use of zero-current-switched quasi-resonant converters (ZCS-QRCs) as power factor preregulators (PFPs) is studied. The study is applicable to boost, buck-boost, flyback, SEPIC, and Cuk topologies. The main conclusion is that the switching frequency variation range using a half-wave resonant switch is lower than that using a full-wave resonant switch if the load connected to the output is almost constant. Moreover, using topologies with a transformer (flyback, SEPIC or Cuk), this variation range can be minimized choosing an adequate value of the normalized switching frequency at the peak of the sinusoidal input voltage. However. this range increases greatly when the load changes in the same manner. In this case, a reduced switching frequency variation range is obtained using a full-wave switch. However, this type of resonant switch decreases the efficiency because it handles reactive energy, and then a trade-off between switching frequency variation range and efficiency must be considered [54] J. S. Glaser and A. F. Witulski, "Application of a constant-output-power converter in multiple-module converter systems," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 909. The origins of the current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems are explored. Both problems are studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems, and that converters which behave neither as current nor as voltage sources can share a load equally in an <i>a</i>×<i>b</i> array of converters. One class of converters useful in such systems is that characterized by constant output power (e.g., the clamped series resonant converter). Furthermore, it is shown that constant output power converters are a subset of a broad class of converters whose output voltage is load-dependent, all of which exhibit particular load-sharing good voltage- and current-sharing characteristics. The characteristics of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A small-signal model of the modular converter system is developed. Experimental results are given [55] W. J. Gu and K. Harada, "A novel, self-excited, pwm forward converter with zvs resonant transition using two minor-loop-operated saturable cores," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 85. A self-excited forward power converter is proposed. The turn-on and turn-off transitions of the switch are zero voltage switched resonant transitions. Two saturable cores operated in minor <i>B</i>-<i>H</i> loop are used to achieve such transitions. The waveform of the voltage across the switch is trapezoidal, and the current flowing in the switch is a quasi-square-wave. The switching losses are considerably reduced, and the stresses in the switch are significantly suppressed. The converter has load characteristics similar to those of a square-wave pulse-width-modulated (PWM) forward converter. The on duty ratio is modulated by a small current applied to the winding of one core. Experiments on a 350 kHz, 100 W DC-DC power converter show good performance [56] S. Hamada, Y. Maruyama, and M. Nakaoka, "Saturable reactor assisted soft-switching technique in pwm dc-dc converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 93. A family of saturable-reactor-assisted soft switching pulse-width-modulated (PWM) DC-DC power converters is presented. It uses saturable reactors to achieve efficient soft switching in a wide load range, from no-load to full-load, with no substantial increase in conduction losses. An approximate analysis and key experimental results are presented. In addition, a summary of voltage conversion ratios and voltage and current stresses for this family of converters is provided [57] K. Harada and K. Harada, "Dead angle compensation using inductor in dc-to-dc converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 649. An analysis of a circuit for dead angle compensation in a DC-to-DC converter controlled by a magnetic amplifier is presented. This circuit suppresses the dead angle so that the core loss can be reduced without spoiling the current surge suppression characteristics of the magnetic amplifier. The magnetizing characteristics of the core containing the saturation inductance and the reverse recovery of the diode are modeled. The control characteristics of the converter with the compensation circuit can then be expressed analytically and the limit of compensation derived theoretically. It is found that there is a condition of the inductor in the circuit for which the head angle caused by the recovery of the diode is reduced to zero. Compensation is limited by the saturation inductance of the core. Therefore, a core of good rectangularity has to be used at high frequency [58] H. Hashimoto, Y. Ishikawa, F. Harashima, A. Rudev, and V. I. Utkin, "Application of sliding mode control using reduced order model in induction motor," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 259. Under the assumption that the dynamics of an induction motor consist of some partial motions of different rates, two different types of reduced-order system (of first and third orders) are obtained using the method of singular perturbation theory. Correspondingly, a very simple control algorithm based on sliding mode control is designed. In the first case the electromagnetic dynamics is neglected: in the second the processes associated with leakage fluxes are neglected. The motor slip and phase are handled as control actions and designed as discontinuous functions of control error, which is steered to zero by enforcing sliding modes. An experiment setup using analog circuitry for a 4p-induction motor with a power of 0.91 W and a three-phase voltage of 160 V was designed, assembled, and tested [59] A. Hassan, G. Bornard, S. Bacha, and M. Brunello, "Definition and application of a nonlinear control law for series resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 793. A nonlinear control law for a class of resonant converters is proposed. The departure point is the mathematical models found in a previous work, to which a stabilizing feedback law is applied. The theory is confirmed by simulations. The principle of the control law consists in finding a state feedback which makes a given submanifold attractive. The proposed control law is defined everywhere (i.e. it has a global character), is stable, and does not depend on the load variations, so that it constitutes a robust manner of control [60] N. Hemati, "Dynamic analysis of variable-reluctance permanent-magnet brushless dc motors," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 989. Dynamic characteristics of permanent-magnet brushless DC motors (BLDCMs) in the presence of reluctance variations are formulated and analyzed. The local dynamics are presented, since a high percentage of currently available BLDCM systems are accompanied with linear velocity and current controllers. The notion of an equivalent DC motor model is presented, and its validity is examined [61] K. Heumann, C. Keller, and R. Sommer, "Behaviour of igbt modules in zero-voltage-switch applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 19. A zero-voltage switching (ZVS) test circuit for power semiconductor devices in which these devices are stressed in a similar way as in a resonant DC link inverter is presented. Different types of 50 A insulated gate bipolar transistor (IGBT) modules (fast switching type and low saturation type) were investigated under hard switching and soft switching conditions. The turn-off behaviour and the power dissipated in the modules were measured using different resonant frequencies in the ZVS test circuit. By using ZVS, the switching energy can be reduced by a factor of approximately 9 for the fast switching device and by a factor of approximately 6 for the low saturation device compared to the hard-switched case [62] T. Higashi and T. Ninomiya, "Large-signal transient response of resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 807. Large-signal transient responses of voltage-mode resonant converters are investigated by analysis and experiment. The maximum peak values of the voltage stress on the semiconductor switch, reactor current, and output voltage are obtained for the step-change of the input voltage and of the load current. Comparison of large-signal transient responses for various resonant converters shows that full-wave resonant converters entail a much higher voltage-stress on the semiconductor switch compared with their half-wave counterparts, and that forward-type converters show a faster output voltage response that other quasi-resonant converters [63] J. Holtz, "Pulsewidth modulation-a survey," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 11. Pulse-width modulation (PWM) is surveyed with reference to performance criteria, feedforward schemes, and feedback PWM control. It is stressed that the implementation of PWM techniques in the design of AC motor drive systems depends on the machine type, the power level, and the semiconductor devices used in the power converter. It is ultimately performance and cost criteria which determine the choice of a PWM method in a specific application [64] J. Hsieh and C. C. Liu, "An integrated knowledge- and algorithm-based method for power converter design," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1316. A knowledge-based system (KBS) is developed as a computer-aided tool for power converter designers. The knowledge acquired from experienced designers is generalized and extended in the KBS. The algorithm-based methods are integrated with the KBS to overcome the difficulty of incomplete design knowledge. This integrated method is intended to reduce the design time and costs. Practical converter design examples are provided [65] C. Hua and R. G. Hoft, "High performance deadbeat controlled pwm inverter using a current source compensator and nonlinear loads," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 443. A control technique which generates high-quality sinusoidal output voltage form a single-phase pulse-width-modulated (PWM) inverter suitable for uninterruptible systems is presented. A scheme for combining the deadbeat control with a current source compensator is proposed, and the control mechanism is analyzed. A current source compensator is used to compensate the voltage drop at the firing instant of a triac-controlled resistive load. The PWM is determined at every sampling instant by the proposed algorithm. Simulation results show that the scheme can produce nearly sinusoidal waveforms for nonlinear loads [66] G. Hua, C. S. Leu, and F. C. Lee, "Novel zero-voltage-transition pwm converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 55. A class of zero voltage transition (ZVT) power converters is proposed in which both the transistor and the rectifier operate with zero voltage switching and are subjected to minimum voltage and current stresses. The boost ZVT-PWM converter is used as an example to illustrate the operation of these converters. A 300 kHz, 600 W ZVT-PWM boost, DC-DC converter, and a 100 kHz, 600 W power factor correction circuit using the ZVT-PWM technique and an insulated gate bipolar transistor (IGBT) device were breadboarded to show the operation of the proposed converters. It is shown that the circuit technology greatly improves the converter performance in terms of efficiency, switching noise, and circuit reliability [67] D. Y. Huh, H. S. Kim, and G. H. Cho, "New group of zvs pwm converters operable on constant frequency and its application to power factor correction circuit," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1441. A zero voltage switching (ZVS) PWM power converter family is obtained by using a new ZVS PWM module (ZPM) with a saturable inductor which prevents the diode junction capacitors and the commutation inductor from resonating. The new converters show almost all the characteristics of the conventional PWM converters. A boost ZVS PWM converter is applied to a power factor correction circuit. It operates on a continuous conduction mode. Experimental results for output power of 1 kW are presented [68] D. Y. Huh, H. H. Sung, and G. H. Cho, "Comparative study of electronic transformers using resonant and nonresonant switching converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1433. Five different topologies for AC choppers are studied. Among them are the soft switching power converters ZCS (zero current switching) QSRC with three switches, half-bridge ZCS QSRC, ZVS (zero voltage switching) step down converter with two switches, and ZVS step-down converter with small current ripple. They are applicable to AC choppers requiring four-quadrant operation. The two-step driving-down converter has the lowest current ripple and acceptable switching loss and is the most suitable for implementing a small, lighter, and more economical high-power system (>1 kVA) [69] S. Y. R. Hui, K. K. Fung, and C. Christopoulos, "Decoupled simulation of multi-stage power electronic systems using transmission-line links," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1324. The application of the transmission line modeling (TLM) method to the decoupled simulation of multistage power electronic systems is described. Stiff capacitively or inductively smoothed DC links in power electronic systems can be modeled as two port transmission line links using the TLM method. The TLM links enable the circuits connected by the links to be decoupled and simulated as individual circuits, resulting in smaller system matrices, the possibility of parallel computation, and reduction in computing time. Interaction between these linked circuits can be realized by exchanging the incident pulses at both ends of the transmission line links. Computer simulations of an AC to DC converter used in a teaching laboratory confirm the simplicity of the TLM decoupled simulation approach [70] F. A. Huliehel, F. C. Lee, and B. H. Cho, "Small-signal modeling of the single-phase boost high power factor converter with constant frequency control," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 475. A simple and accurate small-signal model for the high-power-factor converter with constant switching frequency is developed and verified. The model is applicable to all frequencies below half the switching frequency. The model is useful in the design and analysis of the voltage and current loops, and of the input and the output impedances of the converter. The use of the model is demonstrated in the analysis and design of a power factor boost converter with average current control [71] K. Iida, T. Kishmoto, H. Matsuo, F. Furokawa, and M. Asano, "Two-phase buck-boost type 100 kw dc-dc converter developed for the electric railway rolling stock," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 417. A two-phase buck-boost-type high-voltage/high-current DC-DC converter is proposed, for application to an auxiliary power source in electric railway rolling stock. The main load of the converter is a three-phase inverter which supplies AC power to an inverter-type air-conditioner, by experiments. The circuit behavior and the operation modes are examined, and the steady-state and dynamic characteristics are analyzed using the averaged equivalent circuit model [72] D. R. Irvine, V. J. Gosbell, and D. Platt, "The switching operation of power bjts at low voltages," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 877. The switching behavior of power BJTs at low voltages is investigated and compared with high-voltage operation to gain understanding of transistor behavior in soft-switching circuits. A one-dimensional model of the power transistor based on semiconductor physics is used to simulate the switching operation of a power BJT in a chopper circuit under both high and low voltage supply conditions. Simulation results are verified by experiment, and a physical description of the switching process at low voltages is presented. The transistor is found to operate in quasi-saturation during both the rise and fall times when operating with a low voltage supply, resulting in much longer rise and fall times. The phenomenon of current tail is also investigated and is found to be a problem at low voltages as well as high voltages [73] E. Ismail and R. W. Erickson, "A single transistor three phase resonant switch for high quality rectification," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1341. Three new classes of low-cost 3φ AC-DC high-power-factor/low-harmonic controlled rectifiers are derived from parent DC-DC power converter topologies containing boost-type inputs, buck-type inputs, and quasi-resonant zero-current-switch (ZCS) buck-type inputs. With a single active switch in addition to the diode bridge rectifier, the converters are capable of drawing a high-quality input-current waveform naturally at nearly unity power factor. Thus a simple 3φ AC-DC high power factor rectifier is obtained. Simulation and experimental results are supplied to demonstrate the validity of the concept [74] P. Jain and H. Soin, "A constant frequency parallel tuned resonant dc/dc converter for high voltage applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 71. A constant-frequency resonant DC/DC power convertor topology for use in high-voltage, high-power systems with ultralow output voltage ripple requirement is presented. Possible modes of operation are described and an efficient mode of operation is selected. Steady-state analysis of the converter is given, and performance curves are presented. A generalized curve describing the region of zero voltage switching is given. Experimental results for a prototype converter operating at 128 kHz and delivering 55 V, 28 A DC from a nominal 375 V DC bus are presented. They show an overall efficiency between 96% and 93% from full load to half load, and an output voltage ripple of less than 0.1% [75] Z. Jakopovic, "Computer controlled measurement of power mosfet transient thermal response," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1025. A measurement system for the computer controlled power MOSFET transient thermal response is presented. On the basis of a measured semiconductor's temperature sensitive parameter (TSEP), the transient thermal impedance curve (TTIC) is calculated. Using THERM software and TTIC measured points, an identification of the semiconductor's thermal model equivalent parameters is provided. A comparison of measured and approximated TTIC shows that the procedure is very exact [76] S. G. Jalali, I. Dobson, and R. H. Lasseter, "Instabilities due to bifurcation of switching times in a thyristor controlled reactor," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 546. The authors describe two bifurcation instabilities of a thyristor controlled reactor (TCR) circuit in which switching times suddenly change and system stability is lost. The instabilities are unexpected because they are quite different from what might be expected from conventional theory in that they occur without the usual indications such as eigenvalues of a Jacobian matrix crossing the unit circle. The instabilities are explained and their mechanisms are illustrated by the simulation of a static volt-ampere-reactive (VAr) example with realistic parameters. In particular, it is shown how distortion of voltage and current waveforms can cause a thyristor switch-off time to disappear or a new thyristor switch-off time to suddenly appear. The consequence of the sudden change in switch-off times is that stable periodic operation of the circuit is lost and a transient will occur until the circuit settles down to a new steady state [77] H. Jin, G. Joos, M. Pande, and P. D. Ziogas, "Feedforward techniques using voltage integral duty-cycle control [for power convertors]," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 370. Two power convertor feedforward techniques (reset integral control and modulated integral control) based on the integral duty-cycle control concept are investigated. While retaining the performance features of the conventional voltage feedforward technique in terms of input harmonics and disturbance rejection these techniques also correct automatically the errors caused by switching losses. Modulated integral control is also capable of compensating for the effect of switching delays on the input. The attenuation of input source harmonics achieved by these two techniques is evaluated quantitatively. Design considerations are discussed, and experimental results on a 1 kW prototype confirm the feasibility and features of the proposed techniques [78] K. Jin, S. B. Dewan, and J. D. Lavers, "Voltage loop design for a low-ripple fast-response ac/dc switchmode magnet power supply," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1105. Voltage feedback loops for AC/DC switch-mode magnet power supplies are designed and analyzed. In order to achieve low-ripple fast-response voltage loop performance, proper structures of feedback controllers and output filters are identified. In addition, feedback loop stability is analyzed, and the safe operation region of the system is determined, taking into account the nonlinearity of the pulse-width modulator. Results from an experimental breadboard are provided for verification [79] L. Jung-Hoon, K. Jong-Sun, C. Se-Kyo, L. Ju-Jang, and Y. Myung-Joong, "Design of continuous sliding mode controller for bldd motor with prescribed tracking performance," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 770. A continuous, accurate and robust sliding-mode tracking controller with a disturbance observer is presented for a brushless direct drive servo motor (BLDDSM). Although the conventional sliding-mode control (SMC) can give the desired tracking performance, there is an inevitable chattering problem which is harmful to a direct drive system. The continuous SMC can be obtained by the efficient compensation of the disturbance observer. The proposed sliding mode control with bounded stability is theoretically investigated in detail. The design of the sliding mode tracking controller for the prescribed accurate and robust tracking performance without the chattering problem is possible using the results of a detailed stability analysis. The prescribed tracking performance and the robustness of the proposed algorithm are demonstrated through the computer simulations for a BLDDSM under load variations and parameter uncertainties [80] H. J. Kim, C. S. Leu, R. Farrington, and F. C. Lee, "Clamp mode zero-voltage-switched multi-resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 78. A method for improving the performance of zero-voltage-switched multiresonant power converters (ZVS MRCs) is proposed, based on clamping the drain-to-source voltage of the power switch using a soft switching nondissipative active clamp network. Complete DC analysis and design guidelines for the clamp-mode forward ZVS-MRC are presented. Device is shown to perform significantly better than forward ZVS-MRCs without an active clamp [81] H. W. E. Koertzen, J. A. Ferreria, and J. D. van Wyk, "A comparative study of single switch induction heating converters using novel component effectivity concepts," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 298. A set of criteria for comparing rival single-switch induction heating power converter topologies are introduced. Three single-switch topologies are compared using a transmission efficiency study backed by extensive simulation and experimental measurement. The power handling capability of components is compared with the active power delivered by the power converter. This method of rating involves detailed analytical modeling and experimental verification [82] Y. Konishi, N. Arai, K. Kousaka, and S. Kumagai, "A large capacity current source pwm converter with sinusoidal inputs and high power factor," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1361. The authors describe a method for selecting pulse width modulation (PWM) patterns and a method for designing low-pass filters in large-capacity current source PWM power converters, to suppress higher harmonics flowing into the power supply. A test carried out on a 500 kVA PWM converter, employing the proposed methods, verified that they substantially decrease higher harmonics flowing into the power supply. The test also showed highly efficient converter characteristics with a supply power factor equaling almost 1.0 [83] R. Kraus, K. Hoffmann, and H. J. Mattausch, "A precise model for the transient characteristics of power diodes," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 863. A power diode model for circuit simulations is described. All important phenomena like transient behavior, temperature dependence, emitter recombination, mobile charge carriers in depletion layer, carrier multiplication, and self-heating are included. Comparisons between simulations and measurements show less than 10% deviation of current and voltage over the temperature range of 25°C-125°C [84] A. Kurnia, O. H. Stielau, G. Venkataramanan, and D. M. Divan, "Loss mechanisms in igbts under zero voltage switching," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1011. Loss characterization of IGBTs under zero voltage switching conditions is needed to understand operating limits for soft switching converters such as the resonant DC link inverter. Several important loss mechanisms which can be identified include turn-off switching loss due to tail current `bump', dynamic saturation and snubber dump loss during turn-on, elevated conduction loss due to imperfect conductivity modulation under <i>di</i>/<i>dt</i> conditions snubber dump at device turn-on, loss associated with energy trapped in the device package internal inductance, and losses associated with uneven current distribution within the device. These loss components are quantified, and experimental validation of total device losses is presented [85] Y. Kuroe and T. Yamamoto, "Computer aided sensitivity-analysis of power electronic control systems and its applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1293. Proposed are computer-aided algorithms for computing sensitivities for power electronic control systems with closed-loop control circuits. It is pointed out that, in the sensitivity analysis of closed-loop power electronic systems, it is necessary to analyze sensitivities with respect not only to usual circuits parameters but also to the switching states of the power semiconductor devices determined by the triggering signals. The adjoint network approach is extended in order to compute the sensitivities with respect to both the usual circuit parameters and triggering signals of power semiconductors. An optimal design method by using the sensitivity calculations is also developed [86] L. Laskai, T. S. Wu, and M. Ehsani, "Inductor coupled converter (ic<sup>2</sup>) for high-power dc-dc applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1085. The suitability of the inductor coupled converter (IC<sup>2</sup>) and its extension is analyzed for high-power DC-DC conversion. Moderate device and component stresses and zero-loss switching, make this converter a good candidate for applications where both voltage step-up and voltage step-down are required. Analysis shows that, due to the circulating currents, device current rating is a limiting factor in the scalability of this topology to very high powers. Simulation and experimental prototype results are included to demonstrate the operation of the converter [87] G. Ledwich, E. Da Silva, and T. A. Lipo, "Soft switched notching current source inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1093. An improved soft switched current source converter structure is reported. An evolution of possible forms is presented, and the operation of the circuit is explained. A simulation study illustrates the quality of closed-loop modulation in synthesizing a three-phase sinusoidal voltage under the soft switching constraints. An evaluation of the loss mechanisms in this structure is performed, and the relative loss terms are compared for a particular high-power thyristor. The primary disadvantage of the circuit is the voltage stresses, which are appreciably higher than line-to-line voltage but are roughly the same as that of current proposed soft switched CSI systems [88] E. S. Lee and T. G. Wilson, Jr., "Electrical design inspection of electronic power supplies via time-domain circuit simulation," in 1992 IEEE Workshop on Computers in Power Electronics (Cat. No.92TH0504-1), 1992, pp. 29. In the 1992 Power Electronics Specialists Conference, the authors presented electrical design inspection (EDI) as a methodology for using circuit simulation in the design and development of electronic power supplies. This presentation in the 3rd IEEE Workshop on Computers in Power Electronics is a follow-up to that work. They discuss various aspects of the EDI methodology that have not been addressed in the cited paper, with special emphasis on device modeling and software implementation. Finally, they present new results of applying the EDI methodology to a 150 W DC-DC power converter with voltage mode control, operating at 500 kHz [89] E. S. Lee and T. G. Wilson, Jr., "Electrical design inspection: A methodology for using circuit simulation in the design and development of electronic power supplies," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 34. An electrical design inspection methodology, that combines advanced power circuit simulation techniques and RISC (reduced instruction set computing) workstation hardware in the day-to-day design of electronic power supplies is presented. This methodology is embedded in an electrical design inspection system that detects one class of design mistakes and prevents them from propagating further in the product realization process. The methodology, and the implementation of the system are described. Preliminary results from applying this methodology to electronic power supply products are presented. Future enhancements to the methodology and how it can benefit the product realization process are discussed [90] P. W. Lefley and G. M. Asher, "Steady state operation of a controlled hidden-link induction motor drive," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 119. The controlled operation of the naturally commutating hidden link power converter driving a cage induction motor is described. The motor is shunted by excitation capacitors such that the motor-capacitor lead operates at a leading power factor above 35 Hz. It is shown that, in the lagging power factor region, the drive yields acceptable performance for fan and viscous type loads, suggesting that the drive is applicable to variable frequency starting of high-power induction motor drives. The authors describe an experimental rig controlled by an 80C196 processor performing speed and current control. Current and voltage waveforms in the lagging and leading power factor regions are given [91] R. Liu, C. Q. Lee, and I. Batarseh, "A unified approach to the design of resonant power factor correction circuits," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 181. It is shown that current-driven DC-to-DC resonant power converters can be utilized in designing resonant power factor correction circuits (RPFCCs). Depending on whether the energy stored in the tank circuit is programmable or not, the RPFCCs can be classified into two sets. The RPFCCs falling into the first set possess the potential to have both high power factor and fast output regulation, while the RPFCCs in the second set can only provide high power factor. Five control schemes for the RPFCCs based on the classification are presented. Design examples and computer simulations are also presented [92] J. M. Lopera, M. Pernia, J. Diaz, J. M. Alonso, and F. Nuno, "A complete transformer electric model, including frequency and geometry effects," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1247. An electric model for transformers, including both frequency and geometry effects, is presented. From Maxwell's equations an electric circuit which represents the transformer behavior is obtained. Expressions for calculating the circuit parameters from the winding layer geometry are given. The model's inclusion in simulation programs and its limitations are discussed. Experimental results showing the accuracy of the model are provided [93] A. W. Lotfi, Q. Chen, and F. C. Lee, "A nonlinear optimization tool for the full-bridge zero-voltage-switched dc-dc converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1301. The fundamental equations characterizing the full-bridge zero-voltage-switched (ZVS) DC-DC power converter are utilized in a nonlinear design optimization routine. The design is subject to realistic constraints along with an objective function of minimal total volume and/or maximum efficiency. The routine is used to study the effects of switching frequency, leakage inductance and load range for ZVS on the efficiency and size. Maximum efficiency is shown to occur when ZVS is maintained in the immediate vicinity of full load operation. Experimental measurements confirm computed predictions [94] A. W. Lotfi and F. C. Lee, "Proximity losses in short coils of circular cylindrical windings," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1253. Proximity losses in short coils composed by cylindrical wires of circular cross sections are investigated. The main factor involved in proximity losses, the effect of window fill, is studied. Analytical solutions to the two-conductor problem show that the proximity effect can increase losses by up to three times the isolated skin effect loss. A 2D finite element analysis is employed to study systems consisting of a large number of conductors. It is shown that the introduction of conductor-to-conductor spacing can reduce proximity losses. The ranges of validity of the approximate one-dimensional equivalent sheet approach are determined [95] M. Madigan, R. Erickson, and E. Ismail, "Integrated high quality rectifier-regulators," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1043. A family of AC-to-DC converters which integrate the functions of low harmonic rectification, low frequency energy storage, and wide bandwidth output voltage control into a single converter containing one, two, or four active switches is presented. These converters utilize a discontinuous conduction mode input inductor, an internal energy storage capacitor, and transformer secondary circuits which resemble the bridge, forward, flyback, or Cuk DC-DC converters. A large-signal equivalent circuit model for this family which uses the loss-free resistor concept is presented. Design strategies and experimental results are given. High performance regulation with satisfactory line current harmonics is demonstrated with conventional duty ratio control. Further improvements in line current are possible by simultaneous duty ratio and switching frequency control [96] M. S. Makowski, "Switch voltage control versus switch current control method-principle and realization," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 749. New control methods for DC-DC voltage and current converters are studied. A brief introduction to switching network graph theory, focusing on the duality concept, is given. Starting with the open switch voltage control method, which is the topological dual of the current-programming technique, a comparative study of switch control methods reported in the literature is presented. The basic principles, realization, and the resulting performance of the set of control methods and some topological applications to switching electrical networks are discussed. Relevant experiments implementing switch voltage control are presented [97] P. Maranesi and G. Naummi, "Design optimization of switching regulators," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1310. A useful CAD modeling tool for designing DC/DC power converters is presented. It provides open-loop frequency-domain characterization of the switching cell, it helps in the identification of optimal inner feedback, forward compensators, and input filters, it assists the designer in the assignment of the external feedback network, and it expresses the closed-loop transfer functions and plots module and phase frequency responses [98] G. D. Marques, "Stability study of the slip power recovery generator applied to the sea wave energy extraction," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 732. The author discusses the stability of the slip power recovery generator (SPRG), in open loop and in closed loop, for applications like the exploitation of ocean wave energy by water column devices. The stability study was performed using small displacement models for each of the following situations: SPRG in open loop, SPRG with inner current loop, and SPRG with active power regulation. Numerical results obtained for an experimental 3.2 kVA prototype are presented [99] A. Marshall, "Operating power ics at 200 degrees," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1033. Discrete semiconductor devices rated to operate up to 200°C are discussed. It is shown that some aspects of the design used to achieve high-temperature fail-safe operation have resulted in increased device die area, in particular, the stringent layout rules and use of bipolar structures. One of the few outstanding reliability problems for operating devices continually at 200°C is due to the mold compound, and even here experimental materials are available that show promise for improved reliability [100] B. J. Masserant, E. W. Beans, and T. A. Stuart, "A study of volume vs. Frequency for soft switching converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 625. The present study is concerned with determining the volume vs. frequency for the 6 kW converters with forced-air cooling. Both circuits have the same physical layout, but one is operated as a zero-voltage-switching/zero-current-switching (ZVS/ZCS) converter while the other is operated as a more conventional phase-shift converter. Since the switching losses are lower for the ZVS/ZCS converter, its optimum frequency is somewhat higher than the phase-shift converter and its minimum volume is somewhat less. Both circuits actually achieve minimum volume below 20 kHz because of the heat sink requirements, and, if both are restricted to operate above 20 kHz, the volume of the phase-shift converter grows much faster than that of the ZVS/ZCS converter as the frequency increases. It is shown that the volume of the heat sink + reactive components at 20 kHz will be about 70% greater for the phase-shift than for the ZVS/ZCS converter [101] H. Matsuo, F. Kurokawa, K. Iida, T. Koga, and T. Kishimoto, "An improved gate drive circuit using an air core reactor developed for high power gto thyristors," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1237. An improved gate drive circuit for high power GTO thyristors is presented. The energy storage/transfer characteristics of an air core reactor and the fast switching characteristics of FETs are employed to make the high gate current of sharp pulse form. The power loss in the gate drive circuit can be reduced by using the low resistance and the hysteresis comparator to detect and control the steady on-gate current. The proposed gate drive circuit is analyzed, and its usefulness is confirmed by experiments [102] S. Menhart, "Using spice to calculate mosfet operating temperature," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 901. An analog behavioral SPICE model which allows the average temperature of the semiconductor chip of a MOSFET to be determined during a transient simulation is presented. The model is valid for simulation times of less than approximately that of the thermal time constant of the device, and has demonstrated excellent agreement with measured device temperatures. Thermal impedance data required by the model are available from manufacturers' data sheets, so that the model requires no device measurements or characterization [103] M. Meyer, "Active power filters for inverter locomotives-a concept for improved efficiency and low distortion currents," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 389. A concept study for an inverter locomotive equipped with an active power filter is presented. It is shown that the installation of the active power filter, i.e. a small power converter which eliminates most of the distortion current produced by the main converter, is an appropriate method not only for improving the line current spectrum but also for reducing the overall losses of the system. This is shown by means of a simple mathematical model which includes the main effects and allows the system to be optimized for a maximum efficiency. The study is concluded by a sensitivity analysis and proposals for adapted control methods [104] T. A. Meynard and H. Foch, "Multi-level conversion: High voltage choppers and voltage-source inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 397. The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches [105] P. Midya and P. T. Krein, "Optimal control approaches to switching power converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 741. Minimization of a specified cost function is a standard approach to optimal control that unifies large-signal and small-signal performance. Here, quadratic output-error cost functions are considered for power converters. The conventional form of quadratic function is intractable for many converters. Several cost functions which approximate it, but are easier to apply, are introduced. Examples include a cycle-by-cycle quadratic function, a cost function based on the stored energy in a converter, and fast-switching approximations to quadratic functions. These functions are studied for dynamic performance and stability. Results are shown to provide good performance, with little distinction between large and small disturbances [106] M. Milanovic, F. Mihalic, K. Jezernik, and U. Milutinovic, "Single phase unity power factor correction circuits with coupled inductance," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1077. The idea of using coupled inductance in single-phase diode rectifier power factor correction circuits and the influence of the coupling factor on the current ripple are discussed. The circuit proposed for current shaping consists of a boost converter connected to the line and a buck converter connected to the output capacitor [107] L. Moran, E. Mora, R. Wallace, and J. Dixon, "Performance analysis of a power factor compensator which simultaneously eliminates line current harmonics," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1229. The performance and dynamic characteristics of a solid-state power factor compensator which simultaneously eliminates line current harmonics are presented and analyzed. Power factor compensation is achieved by controlling the magnitude and the phase angle (delta) of the transistorized PWM inverter output voltage. Fast response times are obtained by adjusting the amplitude of the PWM inverter output voltage through a modulation index control. The principal advantage of this scheme is that it can maintain a near unity mains overall power factor without sensing and computing the associated reactive components. It can also substantially reduce the harmonic content of the line current when the load is nonlinear. A time domain model is derived and used to accurately predict dynamic behavior and stability region, and to adjust system controllers. The transfer function of the power factor compensator is obtained. Experimental results confirm the operation characteristics obtained by computer simulation and analyses [108] J. C. Moreira, "Torque ripple minimization in switched reluctance motors via bi-cubic spline interpolation," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 851. A method for minimizing the instantaneous torque ripple in switched reluctance (SR) machines is investigated and implemented. The method is based on estimating the instantaneous SR motor torque from the flux linkage versus current and rotor position characteristic curves via a bi-cubic spline interpolation. These coefficients are computed offline, stored in a given memory location of the control processor, and used by two routines that are capable of estimating the rotor position and electromagnetic torque from the phase voltages and currents. The estimated output torque is then compared to a constant reference value, and the result of this comparison drives a current regulator that generates the proper motor phase currents. The ripple minimization scheme is simple and does not require a very fast processor. Its feasibility is confirmed via simulation and some preliminary experimental results [109] W. M. Moussa and J. E. Morris, "Dc and ac characteristics of zero voltage switching pwm converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 236. The authors present an equivalent circuit model for zero voltage switching resonant transition (ZVS-RT) converters operating with constant frequency which takes into account the RT interval. The analysis is carried out by relating the terminal currents and voltages, through the definition of switching functions of the power switches responsible for the ZVS action an equivalent DC circuit model is generated from these relationships. This model is simple and accurate, and can be used to analyze the DC characteristics of the three basic topologies using ZVS-RT: buck, boost, and buck-boost. This technique can be extended to improve the small-signal analysis of these converters, and it can be applied to converters using bipolar junction transistors as switching devices to account for the impact of the switching times of the devices [110] M. Nakahara and T. Ninomiya, "A general computer algorithm for analysis of switching converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1181. A general computer algorithm for the analysis of switching power converters and a software tool called SCAT (switching converter analysis tool) is introduced. The algorithm is fast and efficient because it is based on averaging techniques, but it is sufficiently accurate. In addition, it is so general that any type of converter can be analyzed [111] M. Nakaoka, S. Nagai, Y. J. Kim, Y. Ogino, and Y. Murakami, "The state-of-the-art phase-shifted zvs-pwm series and parallel resonant dc-dc power converters using internal parasitic circuit components and new digital control," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 62. The authors present two circuit topologies for constant-frequency phase-shifted pulse-width-modulated (PWM) resonant full-bridge inverter-type DC-DC high-power converters with a single high-frequency high-voltage (HFHV) transformer AC link, which effectively make the best of parasitic circuit components existing in the HFHV transformer and HV cable. Two resonant circuit topologies are introduced which are concerned with series and parallel-loaded resonant (SPR) tank type and multiresonant (MR) type composed of SPR tank and two zero voltage switched (ZVS) quasi-resonant poles. These converter characteristics are evaluated in terms of computer-aided analytical and experimental results. Real-time direct digital signal processing based model control strategies for two resonant converters treated here have been implemented to improve transient and steady-state operating performance for an X-ray high-power generator in industrial and medical applications [112] D. Naunin and C. Karaali, "Completely digital control unit of a high dynamic synchronous servodrive with minimal hardware investment using a fast microcontroller," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 686. A microcontroller unit with minimal hardware investment that has been designed for the digital control of a highly dynamic AC servodrive is described. The structure of the microcontroller, the Siemens SAB 80C166, and the concept of the external hardware are described. The principle of a three-phase full-bridge and the generation and measurement of three-phase pulse-width-modulation (PWM) signals utilizing the capture/compare unit are discussed. In addition, the structure used for the current and position measurements is described. The three state values (position, speed, and current) are the main components for the control of a servodrive. A cascaded feedback controller with an inner current loop control is realized with this microcontroller [113] K. D. T. Ngo and R. Webster, "Steady-state analysis and design of a switched-capacitor dc-dc converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 378. A switched capacitor DC-DC power converter topology which consists of <i>n</i> stages of semiconductor switches and capacitors is described. The switches connect the capacitors across the input source during the charging phase and then across the load during the discharge phase to step down the input voltage by a nominal ratio <i>n</i>. Further control of the output voltage is possible via current, resistive, or duty-ratio control. Based on the observation that the ripple on the capacitor voltages is generally linear in practice, state-space averaging is used to derive the average state-space equations for a generalized <i>n</i>-stage switched capacitor converter circuit. Both exact and approximate equations which are useful for design are derived for the practical performance parameters. A design procedure based on these equations is described. The analytical results have been verified by extensive simulation by PSPICE [114] V. A. Niemela, H. A. Owen, Jr., and T. G. Wilson, "Frequency-independent-element cross-coupled-secondaries model for multiwinding transformers," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1261. For high-frequency transformers with any number of windings, an equivalent circuit is presented that accurately predicts the effects of AC winding resistance and leakage inductance over a wide range of frequencies. This model is suitable for circuit simulation with nonsinusoidal excitation and nonlinear loads. With the addition of circuit elements to account for magnetizing inductance, core loss, and winding capacitance, the model has the potential to bring about significant improvement in the accuracy of simulation results, which could ultimately eliminate some of the costly trial and error in power converter design [115] R. Nilsen and M. P. Kazmierkowski, "New reduced-order observer with parameter adaptation for flux estimation in induction motors," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 245. The authors present a novel reduced-order observer with parameter adaptation for fast rotor flux estimation in induction motors. The observer is based on the current model of the induction motor represented in field-oriented coordinates. The theoretical principles of the developed algorithm are discussed. Some results of comparative investigations are presented which illustrate the steady-state and dynamic properties of the speed control system with observer and conventional current model [116] Y. Nishida and T. Haneyoshi, "Predictive instantaneous value controlled pwm inverter for ups," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 776. A microprocessor-based pulse-width modulation (PWM) inverter (UPS) that obtains high-quality sinusoidal output voltage even under a rectifier load is proposed for uninterruptible power supplies. The proposed PWM inverter system uses a closed-loop digital feedback with a sinusoidal reference, and the PWM pattern is determined at every sampling instant. A modification that increases the maximum pulse width, which is limited by the computation time in conventional digital approaches, to provide larger output voltage and a repetitive control technique are applied to the proposed control system. A larger maximum pulse width, stable operation, high output voltage accuracy, very low output voltage distortion, and very fast response are realized [117] L. Norum, W. Sulkowski, and L. A. Aga, "Compact realisation of pwm-vsi current controller for pmsm drive application using low cost standard microcontroller," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 680. The authors present a completely digital realization of pulse-width-modulated (PWM)-VSI current controller for permanent-magnet synchronous motor (PMSM) drive application. The current control algorithm, including decoupling and compensation for machine parameter variation, is presented. The controller is implemented in a single-board control computer which is based on a 16 b microcontroller. Experimental results are presented. A 10 kHz sampling frequency for the current control loop was obtained. Current risetime to nominal value of less than 1 ms, without overshoot in the quadrature axis, and speed bandwidth up to 100 Hz were obtained [118] J. M. Noworolski and S. R. Sanders, "An electrostatic microresonant power conversion device," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 997. An electrostatically driven microstructure suitable for use in a monolithic resonant DC-DC converter is presented. The device can be manufactured using existing integrated circuit processing techniques, permitting integration with, switching devices in silicon. The mechanical resonant structure is used in place of an <i>LC</i> tank and in place of a transformer, avoiding the complexity of manufacturing integrated magnetic elements. A monolithic resonant converter using this technology offering high power density is proposed. The device can potentially be driven in a zero-voltage-switched (ZVS) mode, scaling well to higher operating frequencies [119] F. Nuno, J. Diaz, J. Sebastian, and J. Lopera, "A unified analysis of multi-resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 822. The method developed by S. Freeland and R.D. Middlebrook (1987) to analyze the DC and AC behavior of quasi-resonant DC/DC converters is applied to multiresonant converters with a single controlled power switch. From PWM converter generic characteristics, rules for inclusion of three resonant elements are given to achieve a multiresonant topology with zero voltage switching in both semiconductor devices. From these rules, equations that describe the voltages across the transistor and diode are obtained. There are significant differences from quasi-resonant converters. These differences mean that a closed-form solution for several important quantities cannot be found analytically. An algorithm for finding the solution numerically is developed. The method developed can be applied to the most isolated DC/DC converter topologies [120] H. Ogiwara, T. Nishimura, and M. Nakaoka, "New efficient high-frequency load resonant-tank inverter with quasi-current resonant mode sub-circuits using static induction transistors/thyristors and its phase-shifted power regulation scheme," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 327. The authors discuss a resonant capacitor voltage-clamped type half-bridge topology for an instantaneous resonant current vector-regulated high-frequency inverter with phase shifting control, which efficiently operates with zero current soft switched quasi-resonant and load resonant tank circuit subresonant hybrid soft switching schemes. This inverter uses static induction (SI) devices (SI transistors and thyristors) and is more suitable for modern induction heating and melting power supplies industrial production plants. Analytical results and performance evaluations are presented. A breadboard of a trial inverter is demonstrated for the state-of-the-art induction heating power supply and is examined experimentally [121] M. H. Ohsato, S. Inarida, G. Kimura, and M. Shioya, "Characteristics of resonant type five-level pwm inverter used in small-scaled photovoltaic systems," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 726. A resonant-type five-level pulse-width-modulated (PWM) inverter for small-scale photovoltaic systems is presented. The output waveform of this inverter has multiple levels of voltage, achieved by connecting two units of power source in series or parallel. The operation of and experimental results for this inverter are presented. An efficient circuit which uses two inductors with coupling is proposed to attain high efficiency with this inverter. The inverter also exhibits reduced low-order harmonics [122] E. J. Osegueda and K. D. T. Ngo, "Analysis and design of perforated-plate matrix transformers," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1393. The perforated-plate matrix power transformer is analyzed to assess its suitability for low-profile applications. Finite-element simulation suggests that this type of transformer may be approximated as a collection of weakly coupled toroidal cores. Thus, it is possible to derive closed-form expressions relating typical performance parameters, such as magnetizing inductance and losses, to the hole radius, identified as a meaningful design parameter. High peak flux density around the holes appears to be a problem. Nevertheless, it is possible to design a perforated-plate matrix transformer with acceptable magnetizing inductance, efficiency, and power density [123] H. A. Owen, Jr., V. A. Niemela, and T. G. Wilson, "Enhanced cross-coupled-secondaries model for multiwinding transformers," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1269. The cross coupled secondaries model, which models the leakage inductances and resistances between windings of multiwinding transformers, is enhanced to account for magnetic energy stored and power lost in the core and electric energy stored in the winding space. This is accomplished by adding inductive, resistive and capacitive elements to each winding circuit, greatly extending the frequency range for accurate modeling of high frequency transformers [124] S. S. Park and G. H. Cho, "New simultaneous rotor flux and stator current controlled im drive for good dynamic performance applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 665. A high-performance induction motor (IM) drive which is different from field-oriented control (FOC) is presented. In this drive, the rotor flux and the stator current are simultaneously controlled. The drive has the characteristics of good dynamics and fast transient response. Implementation of this drive is very simple compared with the FOC. Although the drive is robust against the rotor resistance variation, a rotor resistance compensation method for controlling the output torque accurately is presented. Simulation results show that the drive scheme can be used for applications requiring good dynamic performance [125] S. S. Park and T. A. Lipo, "New series resonant converter for variable reluctance motor drive," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 833. A resonant-type converter for a variable-reluctance motor drive is proposed to perform zero current switching of all solid state devices. The resonant circuit is partially resonant rather than fully resonant from the viewpoint of the capacitor. The power circuit of the converter can be realized with unidirectional naturally commutated switches. The converter has many advantages, such as low voltage stress or improved voltage utilization, low loss, and no stress in the switching instant. The operating principle and current regulation method are introduced and verified through simulation [126] J. Peracaula and J. Bordonau, "Microprocessor and transputer implementation of ac motor vectorial control," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 691. Two different solutions for vector phase control for AC motors have been implemented, tested, and compared. One of these uses a 16 b microprocessor (80286), with a coprocessor, working at a 33 MHz clock rate. The number of floating point operations to be performed in the computation of the equations involved in vector phase control required the use of a coprocessor in order to unload the task of the CPU and to speed up the process. The second implementation uses two transputers (INMOS T800) working at a 25 MHz clock rate and a serial transmission rate of 20 Mb/s. Due to the processing speed of both implementations, the digital control blocks match the speed conditions imposed by the fast response of the internal current control loops of the physical system. The implementation based on transputers can execute the control algorithm in only 500 ms [127] M. A. Perez, J. Sebastian, J. Diaz, and J. A. Martinez, "The forward discharge converter (fdc): A general solution to obtain soft-switching in any power converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 101. It is noted that soft switching obtained by means of C or LC snubbers and forward discharge power converter forward zero-current-switched QRC like an energy recovery network replaces a simple MOSFET switch without changes in power topology (one or multiple switches) and control circuit (one drive signal for each is holding up). All control strategies (fixed or variable frequency and current of voltage mode) are possible, i.e., pulse-width-modulated (PWM) converters become low switching loss topologies, and high frequency is feasible [128] E. Persson, N. Mohan, and B. B. Banerjee, "Adaptive tolerance-band current control of standby power supply provides load-current harmonic neutralization," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 320. The authors present a standby power supply system which provides the combined functions of power backup and load current harmonic neutralization. The system is based on a four-switch insulated gate bipolar transistor (IGBT) inverter which is operated in either a voltage or a current mode. The voltage mode uses traditional fixed-frequency pulse width modulation control. The current mode uses an adaptive tolerance band scheme to achieve fixed-frequency. The authors discuss the design tradeoffs for the current-mode control, and present performance data for a 120 V, 25 A (peak) single-phase system [129] J. Pforr and L. Hobson, "A novel power factor corrected single ended resonant converter with three phase supply," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1368. A three-phase rectifier stage, enabling a whole class of switched mode and resonant switched mode power converters to automatically draw sinusoidal input currents from a three-phase supply, is introduced. The proposed technique offers advantages including very simple power circuits, simple control and protection, and very-high-quality input currents. The power factor correction method is described, and the analysis, design, and performance obtained from a buck-type single-ended resonant converter with three-phase supply based on this principle are outlined. Results for a 2.5 kW/40 kHz prototype converter, utilizing a single high-speed GTO as the active switching device and operating directly offline from a 415 V three-phase mains supply, are presented to verify theoretical predictions. The measured input current waveforms drawn from the three-phase supply are sinusoidal with approximately unity power factor [130] L. Pinola, M. Ticozzi, and V. Varoli, "The effects of magnetic components losses on the dynamics of coupled-inductors smps," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1331. An original Z transform-based algorithm is used to develop a fast and accurate tool for the dynamic analysis of switch-mode power converters and to achieve insight into the effect of each parasitic. It is shown that iron losses can be neglected without impairing the compliance in the analysis of all the single-inductor converters and also of the two-inductor converters without magnetic coupling. These losses must be included in the modeling of coupled inductor converters, since their effect on the control-to-output gain can jeopardize the feedback loop stability. Experimental data for a low-power prototype are reported [131] H. Pouliquen, K. Elloumi, and M. X. Wang, "Real time pwm control converters using three elements polynomial regulators," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 451. The authors analyze the modeling of inverter-type converters along with a general method for real-time pulse-width-modulation (PWM) control using a three-element regulator. This regulator is first based on an α stability pole placement principle and then on the internal model principle. From an automatic point of view, robustness is evaluated using the Nyquist diagram criterion. The Wonham internal model principle is applied to reject harmonic disturbances of a given rank or to generate the full reference. Several applications are presented and compared. The algorithms presented were evaluated on a converter structure corresponding to an uninterruptible power supply [132] D. W. J. Pulle, C. J. M. Eijkel, J. H. J. Fluitman, H. Leeuwis, and D. J. M. Van Mierlo, "A new magnetoresistive based sensor for switched reluctance drives," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 839. The technical viability of a magnetoresistive-based position sensor specifically suited to switched reluctance drives is demonstrated. The sensor provides a low cost simple robust solution to the problem of providing continuous speed dependent phase advance capabilities for switched reluctance drives. A control scheme using the sensor is discussed together with experimental and simulated results for a simple three phase SR drive. Experimental results demonstrate the effectiveness of the sensor and highlight the importance of phase angle control for switched reluctance drives [133] J. M. Quero, J. M. Carrasco, and L. G. Franquelo, "Adaptive energy feedback control for resonant converters using neural networks," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 800. A neural controller implementing an energy feedback control law is proposed as an alternative to classic control of resonant converters. The energy feedback control, and particularly the optimal trajectory control law (OTCL), is introduced. As a result, the state space is considered to be divided into two subspaces. An analog neural network (ANN) learns to classify these two classes by means of a learning algorithm. An easy implementation of this controller is proposed and applied to a series resonant converter (SRC). Simulation results show a good improvement in the SRC response and confirm the validity of the controller [134] M. Rastogi, R. Naik, and N. Mohan, "Optimization of a novel dc-link current modulated interface with 3-phase utility systems to minimize line current harmonics," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 162. A novel three-phase utility interface is discussed. The interface draws near-sinusoidal currents from the utility and provides a regulated DC output voltage. The performance of the system is optimized. Simulation results for a three-phase, 208 V (line-to-line), 3 kW system are presented. The sensitivity of the interface to unbalances in various system parameters is examined. Simulation results indicate that a total harmonic distortion in the line currents lower than 5% can be achieved by the interface. It is shown that there is minimal degradation of performance with changes in system parameters [135] B. Ray, "Bidirectional dc/dc power conversion using quasi-resonant topology," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 617. A family of zero-current-switching/zero-voltage-switching and zero-voltage-switching/zero-current-switching quasi-resonant bidirectional DC/DC converters suitable for high-frequency operation based on a bidirectional quasi-resonant switch is proposed. These converters are realizable with only two power MOSFETs. Design considerations and guidelines are discussed, and experimental results supporting the proposed concept are presented. The limitation on the level of forward and reverse power imposed by the zero-current and zero-voltage switching requirements is discussed. The use of single-cycle resonant topology and resonant-transition pulse-width-modulation (PWM) topology for bidirectional power conversion is also mentioned [136] R. Redl and A. S. Kislovski, "Source impedance and current-control loop interaction in high-frequency power-factor correctors," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 483. The authors introduce a model for the input port of the high-frequency power-factor corrector and determine the gain of the current control loop. Both the model and the expression for the loop gain are entirely general and can be used for analyzing the source impedance and current control loop interaction of virtually any corrector with any current control method, operating in continuous or discontinuous inductor current mode, and having any source impedance. Based on the model, the electromagnetic interference filter capacitor and the current-error amplifier can be designed to avoid instability of the current-control loop. The loop gain of a boost corrector with average current control was investigated in detail. The system was found to be unstable at low line voltage and at source inductance values frequently encountered in practical applications. A physical explanation for the instability is given together with recommendations on how to avoid the instability. Test data taken from an experimental boost corrector with average current control are in good agreement with theoretical predictions of the model [137] W. A. Relihan, J. A. Ferreira, and J. D. van Wyk, "A modular matrix dc to dc converter for high current low voltage application," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 926. The use of matrix transformers to obtain low leakage inductance in low-voltage, high-current applications is described. The design stresses modularity, so that a system can be expanded to a higher power level without further design. The transmission line output structure is adjusted to match the converter to various loads [138] J. M. Retif and B. Allard, "A pwm asic using stochastic coding," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 587. The authors describe an application-specific integrated circuit (ASIC) design implementing a novel pulse width modulation (PWM) technique. This PWM function is based on the stochastic coding of the driving pulses. This approach allows a small IC area and high-speed generation of pulse sequences. The validity of the proposed PWM has been studied with simulation and experiment. Several limiting operation conditions of the ASIC are also defined. Using the stochastic PWM a three-voltage inverter is shown to be a more efficient solution than the classical PWM and a dual-voltage inverter; fewer harmonics are generated in current and voltage [139] C. T. Rim, N. S. Choi, G. C. Cho, and G. H. Cho, "A complete dc and ac analysis of three phase current source pwm rectifier using circuit <i>d</i>-<i>q</i> transformation," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 489. The circuit <i>D</i>-<i>Q</i> transformation is used to analyze a three-phase, current-source, pulse-width modulated (PWM) rectifier. The DC operating point and AC transfer functions are completely determined. Most features of the converter are clearly interpreted. The output voltage can be controlled from zero to maximum. The system is equivalently an ideal current source in the steady state and can be described in terms of linear circuits. The input power factor can be arbitrarily controlled with a certain control range [140] X. Roboam, B. Dagues, J. C. Hapiot, and J. Faucher, "Elaboration of a simulation software by the sosie method: Validation of a flux observer for induction motor," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 659. The numerical control of a three-phase induction drive studied by the authors involves realization of a high-performance dynamic flux observer. The authors describe the structure, test, and operation of a specialized simulation program using a general simulation methodology named SOSIE. Comparison of experimental and simulated results allows one to detect the influence of a secondary phenomenon not previously taken into account. An adjustment of the simulation program permits the design of an observer with performance corresponding to desired specifications. The following perturbations have been accurately studied: delays and nonlinearities generated by the static converter, such as dead times, and problems related to limited accuracy associated with the numerization of the algorithms (truncation) and the discretization of the variables (sampling) [141] B. Robyns, H. Buyse, and F. Labrique, "Study and implementation of a simplified and robust position digital controller for a pm synchronous actuator," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 981. A digital position control system for a low-power permanent-magnet synchronous actuator is presented. The control algorithm relies on a simplified decoupling state feedback to obtain field orientation and needs only a position sensor. It has been implemented around two 8-b MCS 8051 microcontrollers and tested on a 2 kW machine [142] L. Rossetto, "A simple control technique for series resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 787. A simple control strategy for series resonant converters, based on the control of the state space trajectory, is proposed. The control technique, suitable also for high frequency applications, only implies a linear combination of the converter state variables, maintaining quite linear and load independent control characteristics. Simulated dynamic response and experimental results are reported [143] J. A. Sabate, R. W. Farrington, M. M. Jovanovic, and F. C. Lee, "Effect of switch capacitance on zero-voltage switching of resonant converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 213. The authors present an analysis of the series-parallel resonant power converter (SPRC) that includes the capacitance of the switches. New DC characteristics are obtained, and the regions where the converter operates with zero voltage switching are determined as a function of the switch capacitance. The analysis is also valid for series and parallel resonant converters. The analysis is verified experimentally on a 50 W, 1 MHz SPRC converter [144] H. Sakamoto and K. Harada, "A novel circuit for non-contact charging through electro-magnetic coupling," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 168. A DC-to-DC power converter suitable for noncontact charging a rechargeable cell using electromagnetic coupling is presented. The circuit is a self-oscillated class C DC-to-DC power converter, for reducing the switching loss and the core loss of the transformer. Zero voltage switching is realized by a resonance of the parasitic parameters of the transformer. Through electromagnetic coupling using this class C converter, a noncontact battery charger of 86% efficiency has been achieved, under input and output voltages of 140 V and 6 V, respectively [145] L. D. Salazar, G. Joos, and P. D. Ziogas, "A low loss switching pwm csi," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1098. A low-loss soft-switching CSI topology, consisting of two parallel switches with a midpoint connected capacitor, is proposed. The structure accomplishes zero voltage switching during turn-off without any additional snubber circuit. It is well suited for high power applications requiring the use of two parallel switches. An analysis and design procedure are presented. Simulation results confirm the feasibility of the topology [146] I. Sasada, T. Yamaguchi, and K. Harada, "Methods for loss reduction in planar inductors," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1409. Numerical analyses of the current distribution in a single rectangular conductor sandwiched by a pair of magnetic substrates, which form a base for understanding AC resistance of the conductor, are presented. The inductance and AC resistance of an inductor in which meander coil is embedded in the one magnetic substrate of a pair and is covered with the other with a given air gap between the two substrates are calculated. The role of the air gap in governing tradeoff between the copper losses and the iron losses as well as the value of inductance is shown. Characteristics of inductors fabricated using NiZn ferrites and an embedded meander coil are presented. A mesh coil by which eddy currents losses in the magnetic core can be reduced is described [147] D. S. Schramm, B. W. Williams, and T. C. Green, "Torque ripple reduction of switched reluctance motors by phase current optimal profiling," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 857. Optimal precalculation of the position-phase current profile for current feeding a four-phase, 4 kW switched reluctance motor results in a single-input, linear, decoupled output torque controller that provides low torque ripple. A bicubic spline interpolation was used to model the nonlinear experimental data. The algorithm is based on minimizing both the average and peak current and hence improves the dynamic performance of the novel six-switch, current-fed, 4 kW, 40 kHz IGBT inverter. Test results are presented [148] J. Sebastian, J. A. Cobos, P. Gil, and J. Uceda, "The determination of the boundaries between continuous and discontinuous conduction modes in pwm dc-to-dc converters used as power factor preregulators," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1061. The determination of the boundaries between both modes of conduction (continuous and discontinuous) in PWM DC-to-DC switching converters used as power factor preregulators is studied. When a DC-to-DC switching converter works as a power factor preregulator, its operation point is constantly changing because both the DC voltage conversion ratio and the load `seen' by the converter are constantly changing in each half-sinusoid of the line voltage (input voltage of the converter). Under these conditions, the conduction mode cannot be directly determined. The boundaries between both conduction modes in each angle of the half-sinusoidal input voltage are determined. The conditions for always operating in continuous or in discontinuous conduction modes are determined as well. The results have been verified in several prototypes and simulations [149] M. Seong-Sik, L. Kyu-Chan, S. Jhong-Whan, and C. Kyu-Bock, "A fuzzy current controller for field-oriented controlled induction machine by fuzzy rule," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 265. The authors propose a fuzzy, current-controlled, pulse-width modulation (PWM) which minimizes current ripple using fuzzy set theory at a constant switching frequency. This technique is applied to an electrical drive system with an induction motor and studied by simulation. The results show that the technique performs better than classical methods such as ramp comparison and the hysteresis band control method [150] J. F. Silva, "Sliding mode voltage control in current mode pwm inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 762. The author discusses the application of sliding-mode control techniques to DC-AC converters, driven by dual current mode PWM modulators that maintain constant frequency operation and provide output current clipping facilities. Sliding-mode control is advantageous when the inverter is designed to perform as a switching power operational amplifier, or might withstand a wide range of loads. Its performance is compared with that of other methods [151] C. J. Simpson, J. D. van Wyk, and J. J. Schoeman, "Low-loss dc to ac converter system for stand alone photovoltaic applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 701. A composite converter with a high-frequency link was investigated for stand alone DC-to-AC-conversion applications such as batteries charged by photovoltaic panels. The secondary converter was a supply-commutated high-frequency bridge, while the primary inverter was investigated further. A center-tap transformer inverter was chosen, and two approaches were used to minimize switching losses. The first approach was to implement regenerative snubbers. The second was a new method that forced zero voltage switching (ZVS). A PSPICE simulation of the second method showed soft switching under no-load conditions, while the experimental setup showed soft switching under both no-load and load conditions up to 2 kVA. This approach offers, in addition to ZVS, features such as greatly reduced losses, a high efficiency, and low implementation cost. It is believed that this approach leads to the optimum configuration for DC-to-220 V-AC-conversion for low-voltage photovoltaic and battery application [152] S. Singer and R. W. Erickson, "On the buffering condition implied by the stabilization of the output of switched mode converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1197. The buffering condition in switched mode power converters is discussed, and the input characteristic implied is described. It is shown that it is possible to buffer the output from the input by control techniques. In such cases a power sink characteristic appears at the input terminals, implying a negative (small signal) resistance [153] K. M. Smedley and S. Cuk, "Switching flow-graph nonlinear modelling technique," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1173. A unified graphical modeling technique, the switching flow-graph, is developed to study the nonlinear dynamic behavior of pulse-width-modulated (PWM) switching power converters. Switching converters are variable structure systems with linear subsystems. Each subsystem can be represented by a flow-graph. The switching flow-graph is obtained by combining the flow-graphs of the subsystems through the use of switching branches. The switching flow-graph model is easy to derive, and it provides a visual representation of switching converter system. Experiments demonstrate that the model has very good accuracy [154] M. C. Smit, J. A. Ferreira, and J. D. Van Wyk, "Application of transmission line principles to high frequency power converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1423. An approach to the design and analysis of planar electromagnetic integrated reactive components based on transmission line theory is presented. It is shown that resonance can occur in a transmission line structure with dimensions much smaller than a quarter wavelength. These structures can find application in many high frequency resonant converter topologies [155] V. K. Sood, N. Kandil, R. V. Patel, and K. Kohorasani, "Comparative evaluation of neural network based and pi current controllers for hvdc transmission," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 553. An investigation into a neural-network (NN) -based controller, comprising an NN trained offline in parallel with an NN trained online, is described. This NN controller has the potential of replacing the proportional-plus-integral (PI) controller traditionally used for HVDC (high-voltage direct-current) transmission systems. A simplified theoretical basis for the operational behavior of the individual NN controllers is presented. Comparisons between the responses obtained with the NN and PI controllers for the rectifier of an HDVC transmission system are made under typical system perturbation and faults. It is shown that the combined NN controller can adapt its weights online to provide improved or similar performance, when compared to traditional PI controllers, for small- and large-signal disturbances. The response of this simple NN controller is somewhat slower for very fast transients, perhaps due to the inadequate training [156] M. Sumner and G. M. Asher, "Self-commissioning for voltage-referenced voltage fed vector controlled induction motor drives," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 139. The authors describe an automated self commissioning procedure for voltage-referenced, voltage-fed, vector-controlled induction motor drives. The measurement of the electrical parameters of the motor at standstill and mechanical parameters from open-loop run-up and run tests are described. These procedures are followed by the automatic design of the two quadrature axis current controllers and the speed controller. Results on the design of vector control schemes for two different cage induction motors are presented [157] J. Sun and H. Grotstollen, "Averaged modelling of switching power converters: Reformulation and theoretical basis," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1165. Uniform averaged modeling methods for switching power converters (SPCs) are established. Averaging methods for differential equation systems with continuous right-hand sides are discussed and then generalized to discontinuous ones. It is shown that these methods are applicable to most known types of SPC, including PWM, resonant, and quasi-resonant converters. PWM converters under discontinuous conducting mode are taken as examples to further demonstrate the applicability of these methods. It is shown that the currently used state space averaging and its several extensions can be derived from these methods [158] P. H. Swanepoel and J. D. van Wyk, "Design and optimization of voltage clamps for voltage source inverters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 155. The authors describe various voltage clamp circuits for voltage source inverters, operated either in the hard switching or soft switching mode. The characteristics of the different circuits are compared, and the theoretical results are supported by experimental measurements. Design procedures and design rules are set out and used to optimally design the clamp circuits. The designs are optimized with regard to design time, peak component voltage stresses, and the required minimum on- and off-states of the main switches [159] Y. Tadros, S. Salama, and R. Hof, "Three level igbt inverter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 46. To extend the application of insulated gate bipolar transistor (IGBT) inverters in motor drives to higher voltages, a three-level IGBT inverter has been developed. The power circuit realized and a pulse pattern generator with space voltage modulation are described. A method to control the middle point potential is suggested. The three-level IGBT inverter can be applied to industrial drives with a three-phase supply voltage of 660 V and drives for local traffic with DC line voltage of 600-750 V [160] T. Takeshita and N. Matsui, "Pwm control and input characteristics of three-phase multi-level ac/dc converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 175. The authors discuss the current control and pulse width modulation (PWM) pattern generation of a multilevel power converter which is capable of producing three levels of phase voltage. In the proposed current control, fast response is realized by introducing a converter model in the control algorithm and the effect of parameter difference between the model and an actual system is compensated for through proportional-plus-integral control of current difference. In PWM pattern generation, the balance of two capacitor voltages is taken into account. For the same sampling period, the current distortion factor of the proposed system can be approximately reduced to 60% of that of a conventional two-level power converter. The prototype was made using a digital signal processor, and simulation and experimental results were compared [161] T. Takeshita and N. Matsui, "Dsp-based current control of three-phase ac/dc pwm converter with model reference adaptive identifier," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 496. The authors report the input current control of a three-phase pulse-width-modulated (PWM) converter. The proposed control can realize a unity effective input power factor and a sinusoidal input current waveform. The current control is performed with the instantaneous voltage equation of the converter, and system parameters are identified by a model reference adaptive systems (MRAS). Therefore, high-performance current control is achieved even if the converter parameters are unknown. In the parameter identification, the number of identified parameters can be halved to reduce the convergence time by expanding a conventional MRAS to the complex plane and by shifting the sampling points of the identification from those of the current control. The effectiveness of the current control and parameter identification methods has been demonstrated by simulations and experiments [162] T. Tanaka and T. Ninomiya, "Random-switching control for dc-to-dc converter: Analysis of noise spectrum," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 579. The effectiveness of random-switching control, by which the switching-noise spectrum is spread and its level is reduced, is revealed analytically. The noise spectrum generated by random switching is analyzed by a general approach that uses a noise-generation model and a switching function with a random process. In the analysis, it is shown that the region where the noise spectrum is sufficiently reduced can be expressed in terms of the standard deviation of switching interval. The validity of the analysis is confirmed by using the normal distribution instead of the actual distribution [163] W. Tang, F. C. Lee, R. B. Ridley, and I. Cohen, "Charge control: Modeling, analysis and design," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 503. A power converter control method called charge control is studied. A complete small-signal analysis is performed for the control scheme. Subharmonic oscillation similar to that of current-injection control is found, and the relationship between the subharmonic oscillation and line/load condition of charge control is defined. Design guidelines which guarantee the stability of the control system under given line and load ranges are proposed. The small-signal model was confirmed experimentally [164] M. C. Tanju and P. Jain, "High performance ac/dc converter for high frequency power distribution systems: Analysis, design considerations and experimental results," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1156. The authors describe and analyze AC/DC converter topology for use in a high-frequency space power distribution system. Steady-state analysis of the converter is provided, the performance characteristics are presented, and transient behavior is studied. The proposed converter has close-to-unity rated power factor (greater than 0.98), low total harmonic distortion in input current (less than 5%), and high conversion efficiency (greater than 96%). To verify the concept, a breadboard converter was built [165] V. A. K. Temple, S. D. Arthur, D. L. Watrous, R. W. DeDoncker, and H. Mehta, "Megawatt mos controlled thyristor for high voltage power circuits," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1018. The authors describes first-generation PMOS-controlled thyristors (P-MCTs) that are fairly mature at 600-1200 V and their first successful 3 kV devices. Single devices are shown operating, in surge, at multimegawatt levels. Modules of parallel or series devices have turned off near megawatt loads. The 3 kV MCT is shown operating in an experimental resonant-type circuit aimed at applications in high-power motor drives [166] P. C. Theron, P. H. Swanepoel, J. J. Schoeman, J. A. Ferreira, and J. D. van Wyk, "Soft switching self-oscillating fet-based dc-dc converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 641. The authors introduce a family of topologies utilizing both zero voltage switching and self-oscillation. The Royer oscillator is modified to use MOSFETs as power switches. Thus insulated gate bipolar transistors (IGBTs) can also be used as power switches, enhancing the power capability for higher voltage and current ratings. A further advantage obtained by the use of FET-input switches, compared to the bipolar-transistor-based Royer and Jensen oscillators, is that stable operation can be obtained without the saturation of any core material. This enables very high efficiency of the power converter as well as a very high oscillation frequency. Typical applications of the family of topologies considered include DC-DC converters, high-frequency inverters, and high-frequency link converters. In high-power (>1 kW) applications, the use of IGBTs in the nonlinear resonant pole soft switching self-oscillating inverter will be advantageous to the efficiency, due to the reduced onstate voltage of a minority carrier device [167] R. Tymerski and D. Li, "State space models for current programmed pulse width modulated converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 337. State space models are derived for pulse-width-modulated power converters operating at constant switching frequency under current programmed control. One model neglects the sample and hold effect of the current loop and is therefore representative of the traditional approach taken to modeling current programmed converters. The order of the model is the same as that of the power stage. A second state space model which incorporates the sample and hold effect is derived. The order of this model is two higher than that of the power stage. A comparison of the two models clearly demonstrates the superiority of the second modeling approach. As the models are in state space form they may be quite readily used in a computer-aided-design package for general power converter analysis and design, to determine all transfer functions and associated pole/zero locations of interest [168] F. Umeda, M. H. Ohsato, G. Kimura, and M. Shioya, "New control method of resonant dc-dc converter in small scaled photovoltaic system," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 714. The authors describe a control method for a resonant DC-DC converter in a small-scale photovoltaic system linked up with storage batteries. The converter is suitable for tracking control of storage battery charging. The control method and experimental results are presented. Optimum operation was achieved by the application of the improved control circuit presented. With this circuit, it is possible to implement tracking control for various intensities of solar radiation [169] K. Vangen, T. Melaa, and A. K. Adnanes, "Soft-switched high-frequency, high power dc/ac converter with igbt," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 26. A 20 kVA direct DC/LFAC dual active bridge (DAB) power converter projected for operation at 100 kHz with insulated gate bipolar transistor (IGBT) switches is presented. It has dual-angle, constant-frequency phase shift control, and is soft switched in a large part of the output <i>V</i>-<i>I</i> plane. It also has a high performance digital control system. The topology and its properties are presented. The control strategy and regulation of the loop are examined. Experimental results are shown for both a small-scale model and a full-scale converter [170] G. Venkataramanan and D. M. Divan, "Improved performance voltage and current regulators using discrete pulse modulation," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 601. The authors reexamine the issue of modulation strategies and their impact on performance characteristics such as dynamic control, current ripple, and acoustic noise. It is seen that significant performance improvement can be obtained by factors such as choice of reference frame, the use of space vector strategies, and the use of voltage or current regulator inner loops. The use of synchronous frame regulators is seen to yield significant improvement in overall modulator performance. It results in elimination of fundamental component errors and significantly improved DC bus utilization. The results presented have been extensively verified using simulation and laboratory experiments [171] F. P. Venter, J. D. van Wyk, and J. J. Schoemann, "A comparison of different compensating modes for detrimental power components in electric networks," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 530. The instantaneous power theory was used to obtain different load power components. The possibility of compensating for detrimental power components by means of different compensating modes using hybrid power electronic active filters was investigated in order to obtain the most economically acceptable compensator topology. The theoretical analysis indicates that 85% and 90% of the 5 th and 11 th harmonic, respectively, can be compensated for, while 120% and 112% of the 7 th and 13 th harmonic are compensated. It is shown that a large portion of the detrimental load power can be compensated without a large and expensive energy storage element [172] V. Vlatkovic, D. Borojevic, X. Zhuang, and F. C. Lee, "Analysis and design of a zero-voltage switched, three-phase pwm rectifier with power factor correction," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1352. A three-phase, single-stage, isolated PWM rectifier capable of power factor correction and low harmonic current distortion and at the same time realizing zero voltage switching for all power semiconductor devices is proposed. The circuit is thoroughly analyzed. Design equations and tradeoffs are provided. The performance of the circuit is demonstrated through the implementation of a 2 kW, 91 kHz, digital signal processor controlled prototype. The isolated DC output voltage is regulated at 50 V. The conversion efficiency is around 93% [173] T. Vogler and D. Schroder, "A new and accurate circuit-modelling approach for the power-diode," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 870. A class of bipolar power semiconductor models for time-saving large-topology circuit simulation is presented. The ambipolar diffusion equation is solved numerically including local effects such as carrier-carrier scattering and Auger recombination processes. Thereby, temperature dependent, algebraic expressions for scattering and recombination processes replace any widely used, unphysical effective parameters (high-injection lifetime, mean carrier concentration, average mobility). Thus, device simulation features are used to simulate large circuits, including power semiconductors, effectively, which is impossible with the device simulation itself [174] E. von Westerholt, M. Pietrzak-David, and B. de Fornel, "Extended state estimation of nonlinear modeled induction machines," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 271. The authors report on the extended state estimation of induction machines. Based on a smoothly nonlinear machine model, local observability is analyzed for operation both with and without a speed sensor. An extended Kalman filter is designed so as to estimate not only electromagnetic quantities and the rotation speed, but also the load torque. Simulations demonstrate its excellent performance for sensorless field-oriented control [175] V. Vorperian, "A fractal model of anomalous losses in ferromagnetic materials," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1277. A simple fractal, or hierarchical, circuit model is presented which simulates the anomalous loss behavior in ferromagnetic materials as a function of frequency and peak flux density. According to this model, the anomalous losses comprise a cascade of scaling eddy current losses. The terminal voltage and current of this model are related by a fractional derivative, which is a generalization of the well-known relationship for an inductor. Experimental results reported previously are easily reproduced using this model [176] A. Wang and S. R. Sanders, "On optimal programmed pwm waveforms for dc-dc converters," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 571. The use of programmed pulse width modulation (PWM) versus regular PWM to reduce the magnitude of the peak harmonic in various DC-DC converter circuit waveforms was investigated. Significant reduction was found possible with a variety of spectral weighting. In the experimental set-up, a reduction in the power of the peak harmonic to approximately one-ninth was achieved in a commercially available power converter [177] X. Wang and B. T. Ooi, "Real-time multi-dsp control of three phase current-source unity power factor pwm rectifier," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1376. The design of a real-time multi-DSP controller for a high-quality, six-valve, three-phase, current-source, unity power factor, PWM rectifier is discussed. With the decoupler preprocessor and the dynamic trilogic PWM trigger scheme, each of the three input currents can be controlled independently. Based on the <i>a</i>-<i>b</i>-<i>c</i> frame system control and the fast parallel computer control, the pole placement control method is implemented successfully to achieve fast response in the AC currents. The low frequency resonance in the AC filter <i>LC</i> networks has been damped effectively. The experimental results are obtained from a 1 kVA bipolar transistor current-source PWM rectifier with a real-time controller using three TMS320C25 DSPs [178] A. K. Weinberg and P. Rueda Boldo, "A high power, high frequency, dc to dc converter for space applications," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1140. The authors describe a regulated, nonisolated Weinberg boost converter with the following advantages: breadboard efficiency from 95 to 97% at 500 W to 1 kW output power; continuous output current with small current ripple; a boost regulator without right-half plane zero effect giving a high bandwidth response; low switching losses (typically 1% at a switching frequency of 350 kHz); conductance control producing typical first order response: and a wide bandwidth voltage regulation loop (10 kHz, with 80° phase margin), giving superior transient response and reduced output filtering [179] S. H. Weinberg, "A novel lossless resonant mosfet driver," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1003. A low-impedance isolated or nonisolated capacitor driver with negligible practical losses is presented. Peak capacitor voltages are totally predictable, and the driver can self-regulate to drive a 1 nF-10 μF capacitor with unchanged risetime. Circuit results exhibit MOSFET gate-drive losses below 2% of the power lost in classical drive circuits [180] S. H. Weinberg, "A 2 kw power subsystem for microgravity isolation platform experiments," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1127. Work contributing to the development of a 2 kW power subsystem for a future Spacelab microgravity platform is reported. Power transfer through a single-turn floating isolation transformer allows physical independence between Spacelab and the platform. Resonant techniques are used to nullify leakage inductance effects. A power system, based on a single 28 V, 72 A series-resonant converter, and to be realized in space-qualified hybrid technology. achieves an overall efficiency greater than 88% with an efficiency of 94% for the power inverter [181] A. Weschta, "Traction technology of the new class s252 and s447 power units for the spanish railways renfe," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 411. To meet future requirements, the Spanish National Railways Renfe has ordered 75 high-performance locomotives of Class S252 and 71 electrical multiple units of Class S447 with an option of 110 further units. Both vehicles are equipped with modern AC traction technology and digital control systems. The author describes the design of the vehicles, the power circuits of both converter systems, the induction traction motors, and the microcomputer-based control. Both projects clearly show that AC drive systems using induction motors and GTO (gate turn-off thyristor) PWM (pulse width modulation) inverters can be successfully used in modern rail vehicles. Multisystem circuits can be implemented without excessive additional cost. Individual axle control is now state of the art for high-performance vehicles. Microcomputer controls for traction and central functions have made it possible to provide future-proof concepts [182] B. O. Woo and G. H. Cho, "Soft switching four quadrant dc-link inverter generating sinusoidal waveforms," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 306. A soft switching power converter topology for high frequency (HF) AC/DC/AC power conversion which synthesizes the sinusoidal output voltages and results in a considerable reduction of acoustic noise is proposed. The converter achieves soft switching without increasing the voltage or current ratings of devices and has the capability of HF and four quadrant operation. HF operation by soft switching provides several advantages such as high power density, low electromagnetic interference and high dynamic performance. The voltage stresses and the current stresses in this converter are limited to the supply voltage and the link current by the operation of a current free-wheeling circuit, and thus the VA ratings of devices are reduced to those of the hard-switched inverters. Simulation results are presented to verify the operational principle [183] T. F. Wu, C. Y. Hung, C. Q. Lee, and H. T. Lee, "An improved dynamic power distribution control scheme for pwm controlled converter modules," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 1148. PWM gain scheduling control is applied to a load-sharing system driven by different line sources whose voltages vary over a wide range. This system can distribute total output current among converter modules with various current ratings. The large-signal behavior of such a system is verified, based primarily on computer simulation. Based on the small-signal analysis, the design procedure for the current and voltage error amplifiers is shown in detail. The system relative stability is investigated to ensure that the performance requirements are satisfied. It is pointed out that the loop-gain function in a multiple-loop system is not as useful as that in a single-loop system. In other words. the current and voltage error amplifiers or compensators need to be selected based on the system characteristic equation, which is uniquely defined for a system [184] D. Wuest, H. Stemmler, and G. Scheuer, "A comparison of different circuit configurations for an advanced static var compensator (asvc)," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 521. Different circuit configurations for an ASVC are introduced and compared. Investigations are restricted to the stationary behavior with a brief look at parameters for dynamic control of the system. The concepts are extended to series connection of gate turn-off thyristors (GTOs), the multilevel inverter, and the application of more than one inverter. The circuits discussed show very large differences in cost and performance. Therefore, the choice for a certain application has to be made very carefully. The appropriate power rating must be reached by putting a number of GTOs in series. Paralleling of a small number of power circuits may also be considered. For common requirements concerning harmonic distortion of the line current only the best of the circuits allow operation without any filter banks. With three-level inverters and single GTOs as switches the circuits have a power rating of about 14 MVA. To reach 100 MVA would require at least eight GTOs in series [185] E. X. Yang, B. Choi, F. C. Lee, and B. H. Cho, "Dynamic analysis and control design of lcc resonant converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 362. The dynamics of LCC resonant power converters are investigated using a small-signal model which is accurate up to the switching frequency. It is shown that the beat frequency dynamics is not only related to the operating region but also heavily dependent on the output filter design. The authors concentrate on frequency control of LCC resonant converters. Compensator designs are discussed, taking into consideration the strong impact of beat frequency dynamics. The frequency-domain analyses are verified using accurate large-signal simulations [186] E. X. Yang, F. C. Lee, and M. M. Jovanovic, "Small-signal modeling of lcc resonant converter," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 941. Small-signal modeling based on the extended describing function concept is applied to LCC resonant converters. The analytical model developed includes both frequency and phase-shift control. Small-signal equivalent circuit models are also derived and implemented in PSPICE. The models ae in good agreement with the measurement data [187] W. Yi, H. L. Liu, Y. C. Jung, J. G. Cho, and G. H. Cho, "Program-controlled soft switching prdcl inverter with new space vector pwm algorithm," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 313. A soft-switched space vector pulse-width-modulated (PWM) inverter is developed using a novel parallel resonant DC link (PRDCL). This PRDCL can operate on variable DC link pulse position and width, resulting in enhanced PWM capability, which is superior to that of other resonant DC links. A space vector algorithm suitable for this PRDCL inverter is presented. The algorithm eliminates narrow PWM pulses which impede DC link operation. This PWM control, however, requires complex and precise timing sequences in relation to PRDCL operation, which is accomplished by adopting a new programmed controller with a buffer and a programmable timer [188] Z. Zhang and B. T. Ooi, "Multi-modular current-source spwm converters for superconducting magnetic energy storage system," in PESC Record - IEEE Power Electronics Specialists Conference, 1992, pp. 561. The authors point out the advantages of using multiple modules of the current-source, sinusoidal pulse-width-modulation (SPWM), three-phase, six-valve converters as the power conditioner for a superconducting magnetic energy storage system. A high degree of controllability is obtained by using dynamic SPWM trilogic as the operating strategy. Very low switching losses are assured by using two carrier triangles per modulating cycle. By parallel connection of coverter modules and by phase shifting the triangle carriers, the following are the gains: increasing the current capacity to the level required by the superconducting magnet, reducing conduction losses, meeting harmonic standards, without the need for an expensive filter, by harmonic cancellation, and achieving a high frequency bandwidth