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Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang Analysis and Control of Two Switches AC Chopper Voltage Regulator Jin Nan1,2, Tang Hou-Jun1, Bai Liang-Yu1, Geng Xin1 Yang Xiao-Liang2 1 School of Electronic, Information and Electrical Engineering School of Electrical Engineering2 Shanghai Jiao Tong University Zhengzhou University of Light Industry Shanghai Zhengzhou, Henan China China {jinnan, hjtang, bailiangyu, gengxin}@sjtu.edu.cn yangxiaoliang@zzuli.edu.cn Abstract: - In this paper, an improved topology of Buck type AC chopper voltage regulator and its control strategy are proposed. This converter only using two power switches is low cost, easy implemented and the phase synchronized circuit is not needed. The current path is provided in dead-time period by using simple snubber circuit. The over-voltage protection varistor is also applied to absorb the voltage spikes which may destroy the power switches. The voltage spikes in dead-time mode commutation are greatly reduced and the power switches are protected. Furthermore, the feedforward and feedback control strategy is proposed to suppress fluctuations and eliminate the harmonic components caused by power quality problems of the input voltage. The proposed converter could realize wide range voltage regulation with high power transfer efficiency and low total harmonic distortion. The steady-state equivalent circuit and the input power factor are derived through theoretical analysis. The output filter design method is also presented. Based on the theoretical analysis and calculation, an experimental prototype is setup. The simulation and experiment results verify the validity of the proposed design. Key-Words: AC chopper, Voltage Regulator, Pulse Width Modulation, Feedforward and Feedback Control, Power Factor, Voltage Fluctuations 1 Introduction input voltage, input current or inductor current. As a AC chopper converter has been widely used in result, these converters are prone to be disturbed and automatic voltage regulators [1-3], soft-starter and hard to be implemented. In addition, there are speed regulator of the inductor motor [4-6], light voltage spikes across the power switches during the dimmer [7] and so on. There are some kinds of AC commutation process. The previous researches have voltage regulators such as auto-transformer and not given enough consideration to the protection of thyristor phase-controlled voltage regulator. Auto- the power switches. Thus, the switching devices are transformer has a large size and its voltage easy to be destroyed for lack of protection. regulating speed is low. The thyristor phase In this paper, a buck type ac chopper voltage controlled voltage regulator has a relatively fast regulator with snubber circuit is proposed. The response compared with the auto-transformer[8]. bilateral switch is composed of an Insulated Gate However, the low input power factor and large Bipolar Transistor(IGBT) and a fast recovery diode amount of the low-order harmonic currents are the rectifier. Only two switching devices are used major problems. Large passive filter is needed and instead of three or four switches in the previous the system cost is increased. presented plans. Thus, cost is reduced and These problems can be solved by using PWM commutation process is highly simplified. The AC chopper. This chopper converter has some simple and effective snubber circuit consists of an advantages such as high input power factor, fast absorbing circuit and an over-voltage protection dynamics and small size filter. Three switches [9,10] varistor. When the two switches are both switched and four switches [11-15] AC chopper are presented off, they provide a current way to avoid high voltage in the previous presented papers. In these researches, spikes. Therefore, the voltage spikes are reduced the switching patterns are critical and an alternate and safe commutation is realized. path has to be established in dead-time period. DC Based on the analysis of working principle and regenerative snubber capacitor [1,7,11] was used to commutation process, the equivalent circuit and the realize safe commutation and enhance efficiency. input power factor of the proposed converter are However, these converters still have complex derived. The calculation methods of main topologies and control strategies. These component parameters are also investigated. commutation strategies are related to the phase of ISSN: 1109-2734 208 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang The harmonic components and fluctuations in voltage spikes will increase the switching losses and the input voltage can also affect the quality of the reduce the power transfer efficiency. Moreover, the output voltage. In previous researches [6,9], peak switching devices may be destroyed by high voltage voltage or root-mean-square(RMS) voltage were spikes. In previous researches, four switches used as the controller input. These signals change converter and corresponding commutation strategy only one time in each period of the input voltage. are designed to reduce voltage spikes [15]. Thus, the low dynamic response speed is the major In this paper, the snubber circuits are added to problem. In addition, the harmonic voltage problems the power circuit to solve this problem. The snubber caused by input voltage have not been investigated. circuits are composed of absorbing circuits and Therefore, in order to keep the output voltage stable, over-voltage protection varistors. The absorbing a voltage feedforward and feedback control strategy circuit adopts a resistor connected in series with a is proposed. This control strategy adopts capacitor to absorb the voltage spikes in dead-time instantaneous voltage as the controller input. The period. However, the absorbing circuit may not output voltage can be stabilized and the dynamic absorb the voltage spikes completely. When load is response speed is improved. Furthermore, the highly inductive or the output current is high, the proposed control strategy not only can suppress the voltage spikes may destroy the switches directly. On voltage fluctuations but also eliminate the harmonic this occasion, the over-voltage protection varistor is components caused by input voltage quality necessary for the safety of the switches. This problems. As a result, this voltage regulator has snubber circuit design can solve the problems many advantages such as simple structure, easy caused by the voltage spikes in switching process implementation, high input power factor, small size and ensure the safety of the converter. The output filter, low total harmonic distortion and high power filter inductor L is used to store and transfer the transfer efficiency. A prototype is set up based on energy to the output side. The output filter capacitor the theoretical analysis and calculation. The Co reduces the output voltage ripple. simulation and experiment results verified the R p1 validity of the proposed plan. Ra1 Ca1 uL iL 2 Description of the converter Li S1 L There are several types of the ac chopper converter. ii A two switches topology is adopted and the snubber circuits are designed to ensure safe commutation. Ra 2 R p2 The converter topology and commutation strategy ui Ci ucp S2 CO RL uo are discussed as follows. Ca 2 2.1 Converter topology The basic structure of the proposed converter is shown in Fig.1. This Buck type AC Chopper is ZO powered by the source voltage ui. Inductor Li and (a) capacitor Ci construct the input filter to absorb the harmonic currents. S1 and S2 are bilateral switches which are composed of IGBTs and fast recovery diode rectifiers. This bilateral switch structure is shown in Fig.1.b. Compared to other bilateral switch structures, it only uses one IGBT. Thus, the driver circuit is simplified and the cost is reduced. These two switches work in complementary mode. In order to avoid the two switches are on states simultaneously, there is a small dead-time period. In dead-time, the two switches are both switched off. (b) Thus, the inductor current is cut off. The inductive load or output filter inductor will produce voltage Fig. 1 - (a) The topology of two switches Buck type spikes across the switches. In switching process, this AC chopper voltage regulator (b) the structure of bilateral switch ISSN: 1109-2734 209 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang 2.2 Commutation strategy ui and the output voltage uo can be considered as a The voltage regulation function of ac chopper constant value in switching period. When ui>0, the converter is realized by using PWM techniques to operation modes and commutation strategy will be the switching devices. The main operation modes discussed as follows. are defined as: active mode and freewheeling mode. In kTS ~ (k+D)TS, S1 is switched on. The AC For the sake of the safe commutation, dead-time chopper converter works in active mode. As shown mode is added. The PWM control signals are shown in Fig.3(a), the current path is ui-Li-S1-L-RL. In this in Fig.2. mode, the inductor L stores the energy and the current iL increases. The intermediate chopper us voltage ucp is equal to ui. In active mode, the power flows from the voltage source to the load. Rp1 t Ra1 Ca1 Sg1 Li S1 L io Ra 2 Sg2 t us Ci S2 Rp2 CO RL uo t Ca 2 td Sg1 t (a) Sg2 R p1 Ra1 Ca1 t kTS (k D)TS (k 1)TS Fig. 2 - The PWM control signals of the bilateral Li S1 L io switches S1 and S2 Ra 2 Sg1 and Sg2 are the gate signals of S1 and S2. The us Ci S2 Rp2 CO RL uo designed PWM signals work in the complementary mode. The commutation strategy has no relation Ca 2 with the phase of the input voltage or input current. Therefore, the phase synchronized circuit is not needed in this system. This commutation strategy (b) not only simplifies the hardware design, but also Rp1 avoids the phase detector errors. For example, in Ra1 Ca1 previous researches [12,13,15], the PWM signals are controlled by the input voltage phase. When the input voltage contains harmonic components, the Li S1 L io phase detector will be disturbed. Thus, the input Ra 2 voltage phase signal is not accurate. Because Sg1 and us Ci S2 Rp2 CO RL uo Sg2 are controlled by the input voltage phase. The Ca 2 disturbed PWM control signals will make the voltage regulator work unstable. Another filter circuit must be designed to ensure that the harmonic components can be eliminated, and the phase (c) detector can work without harmonic disturbance. Fig.3 - The commutation process of ac voltage The phase detector will make the system complex. regulator (a) in active mode (b) in dead-time mode As a result, commutation strategy used in this paper (c) in freewheeling mode has advantages such as easy implementation, low Ideally, at (k+D)TS, S1 is switched off and S2 cost and high stability. should be switched on. However, for the sake of the As the switching frequency fS is much higher safe commutation and protecting the switching than the input voltage frequency f, the input voltage devices, there is a small dead-time period. In this ISSN: 1109-2734 210 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang period, S1 and S2 are both switched off. In (k+D)TS ucp g (t )ui (t ) ~(k+D)TS+td, S1 and S2 are both switched off and the Vim sin(kD ) converter works in dead-time mode. In dead-time DVim sin( wt ) sin(kS )t mode, there will be voltage spikes caused by the cut k 1 k off of the inductor current. These voltage spikes (5) may destroy S2 or cause high switching losses. The The first term of the right-hand side of equation absorbing circuit composed of Ra1 and Ca1 reduces (5) is the fundamental component and the second the voltage spikes. As shown in Fig.3(b), the current term is the harmonic components around the path is us-Li-Ra1-Ca1-L-RL. When voltage surges, switching frequency fS. The fundamental component high voltage spikes or other potential over-voltage of ucp is proportional to the duty ratio D. When fS is problems occur, the over-voltage protection varistor high, the harmonic components can be absorbed by Rp1, Rp2 can protect the switching devices. small-size output filter. As a result, the filtered At (k+D)TS+td, S2 is switched on. In (k+D)TS+td output voltage of converter can be approximately ~(k+1)TS, S1 is off and S2 is on. The inductor current expressed by: freewheels through the load and S2. The current path ucp g (t )ui (t ) DVim sin( wt ) (6) is S2-L-RL shown in Fig.3(c). The inductor L According to equation (6), the output voltage transfers the energy from the inductor to the load can be regulated by changing the duty ratio D. In side. In this period, the converter works in equation (5), the lowest order harmonics of ucp freewheeling mode. occurs at ωS−ω. The size of the filter components is inversely proportional to the orders of the harmonic voltage. Therefore, the switching frequency fS of the 3 System analysis and calculation PWM signal should be kept high enough to raise the To simplify the analysis and calculation, the order of harmonics to a high level. following assumptions are made: 1 Because the dead-time td is short, only 1~2μs. The Sg1 energy stored in inductor is assumed to be constant in dead-time mode. This mode is ignored in the calculation of the main component parameters. 2 Input LC filter absorbs the high frequency input t harmonic currents. As the switching frequency fS is uL uS uO much higher than the input voltage frequency f, the input power factor is assumed not to be affected by the input filter. kTS ( k D)TS (k 1)TS t The voltage source ui is defined as: uo ui Vim sin(t ) (1) iL where ω and Vim are the angular frequency and the amplitude of the input voltage respectively. iL Io Theoretically, the intermediate chopper voltage ucp can be expressed as: kTS (k D)TS (k 1)TS t ui S1 is on uC ucp (2) 0 S1 is off uC uo The PWM switching function of S1 is expressed as: kTS (k D )TS (k 1)TS t 1 kTS t (k D )TS Fig.4 - When ui>0，the waveforms of the inductor g (t ) k N (3) voltage and current, output capacitor voltage in 0 (k D )TS t (k 1)TS switching period where TS and D are switching period and duty ratio of the PWM control signal respectively. The fourier 3.1 Input power factor analysis series of g(t) with a switching frequency ωS is : Usually, in order to reduce the filter size, the 2sin kD g (t ) D cos( kS t ) (4) switching frequency fS is much higher than the input k 1 k voltage frequency f. In switching period, the input Therefore, ucp is given by: voltage ui and the output voltage uo are considered ISSN: 1109-2734 211 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang to be constant. When ui >0, the waveforms of reduces. The inductor transfers the energy to the inductor voltage uL and current iL are shown in fig.4. load. The inductor current ripple can be expressed The inductor voltage uL is : as: ui uO kTS t (k D)TS ( k D )TS u u (1 D )TS uL (7) iL ki iL o dt o (15) uO ( k D)TS t (k 1)TS kTS L L where ΔiL is the inductor current ripple, ki is current In switching period, the average voltage of the ripple coefficient. The inductor L has to meet the inductor L is: maximum ripple current : uL D(ui uO ) (1 D)uO (8) u (1 D)TS uL can be also expressed as : L o (16) iL k i di u L (t ) L L (9) The output filter capacitor current is : iC = iL−io. dt The output voltage ripple Δuo is given by: According to equation (6), the input current ii is given by: 2 ( k D )TS I T uo uo ku 2 iL io dt L S (17) ii Di L (10) C kTS 8Co The average voltage of ucp is: where Δuo is the output voltage ripple, ku is the diL voltage ripple coefficient. In order to reduce the ucp Dui L uO (11) output voltage ripple, Co has to meet the maximum dt The equivalent circuit of equation (11) is shown in ripple voltage: Fig.5: i kT Co L i S (18) 8uo ku iL L 4 Voltage control strategy design Voltage sags or swells are caused by the disturbances or faults in power systems. Power line Dui ZO uO disturbances in sensitive equipments such as computers, communication equipments, and medical equipments can often lead to the loss of valuable data. According to equation (6), the output voltage can be regulated by the duty ratio. The input voltage Fig.5 - Steady-state equivalent circuit of AC fluctuation also affects the output voltage. Therefore, chopper voltage regulator it is necessary to design the effective controller to Zo is the equivalent impedance of the load R in keep the output voltage stable. parallel with the output filter capacitor Co. Let For fast output voltage control by the voltage Z=Zo+jωL. According to the Kirchhoff’s laws: regulator, a fast control strategy is required. DU i Generally, the previous research used peak voltage IL (12) feedback control method. The peak voltage detector Z with diodes, capacitor, and resistor is used as a The input power factor angle φ of the converter is: voltage sensing circuit. When the input signal is U Z decreased, the capacitor is discharged through the arctg ( i ) arctg ( 2 ) (13) Ii D resistor, and when increased, the capacitor is The input power factor (PF) of the two switches AC charged. However, the peak voltage value changes chopper voltage regulator can be expressed by: slowly compared to the instantaneous voltage value. PF=cosφ (14) A fast peak voltage detector is proposed in [12]. According to equation (14), the PF is influenced by Although it can detect the peak voltage faster, it can output impedance and duty ratio of the control not eliminate the output voltage harmonics caused signal. by input voltage. 3.2 Output filter design Based on the analysis of the commutation The output filter is used to reduce the voltage ripple strategy and working principle, the voltage and keep the current continuous. In ((k+D)TS+td feedforward and feedback control strategy is ~(k+1)TS), the converter works in freewheeling designed. The instantaneous voltage is adopted as mode. As shown in Fig.4, the inductor current the controller input. As a result, compared to RMS voltage control or peak voltage control, the dynamic ISSN: 1109-2734 212 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang performance is improved. In addition, the feedback controller block and then is used to regulate the duty control part can regulate the output voltage with no ratio D. The duty ratio Dfk of feedback control is steady-state error. The feedforward control part can given by: eliminate the voltage harmonic components and D fk k p (uor uO ) ki m(t ) suppress the voltage fluctuations effectively. The (24) dm(t ) control system structure is shown in Fig.6. uor uO dt where kp, ki are proper proportional and integral Df gains respectively. m(t) represents the integral of the output voltage error Δu. The integral part of the designed controller makes the steady-state output ui voltage error zero. D is limited within the range Dh D uo uor from 0 to 1. Thus, D can be expressed as: 1 D (t ) 1 D D f Dh D fk 0 D (t ) 1 (25) uor u D fk 0 D (t ) 0 The digital signal processor is used to implement the control algorithm and calculate the Fig.6 - The feedforward and feedback control duty ratio in experiment. Then, the PWM control system structure diagram signals Sg1 and Sg2 are generated by modifying the The steady-state input voltage is defined as: corresponding register value in DSP directly. uir=uirpsin(314t) (19) The reference output voltage is: uor=uorpsin(314t) (20) 5 Simulation uirp ， uorp are the input peak-voltage and the The voltage regulator shown in Fig.1 is reference output peak-voltage respectively. The implemented with the following parameters: steady-state duty ratio Df at the operation point is: fS=40kHz, Li=100μH, Ci=1μF, C=1μF, L=1mH, Df =uorp/uirp (21) Ca1= Ca2=0.1μF, Ra1= Ra2=10Ω, Ro=40Ω. Because the output voltage is proportional to When D=0.5, the simulation results are shown the duty ratio D. The feedforward control part is in Fig.7. The input current is shown in Fig.7(b). The designed as: intermediate chopper voltage and the output voltage (Df+Dh)ui=uor (22) are shown in Fig.7(c) and Fig.7(e) respectively. The According to equation (22), the duty ratio Dh of input current is nearly sinusoidal waveform. The feedforward control part is: intermediate chopper voltage ucp contains high order Dh=( uor−Df ui)/ ui (23) harmonic components. By using the output filter, In previous researches, input voltage harmonics the harmonic voltage is eliminated and the suppression has not been investigated. The proposed sinusoidal output voltage is obtained. feedforward control uses the instantaneous value of The snubber circuits are designed to reduce the input voltage and the reference output voltage as the voltage spikes in commutation process. Fig.8(a) controller input to regulate the duty ratio. At the shows the voltage across S1 without snubber circuit. operation point, the feedforward control can obtain There are voltage spikes with the amplitude of 20V. Dh to compensate the steady-state duty ratio Df . The This will increase the power dissipation. Fig.8(b) input voltage fluctuations can be suppressed and the shows the simulation results using snubber circuit. harmonics can be eliminated by the feedforward The voltage spikes are highly reduced. As a result, control. In this way, the output voltage is stable with the designed snubber circuit can reduce the voltage low harmonic distortion. This method is simple and spikes effectively and protect the switching devices. effective. According to the circuit structure and the working principle, when ui>uor , the feedforward control can work effectively. Otherwise, the voltage drops can not be compensated. The feedback PI control part is designed to make no steady-state error. As shown in Fig.6, the output voltage is subtracted from the reference voltage. The error voltage passes through PI ISSN: 1109-2734 213 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang voltage is decayed abruptly up to 15% during 3 400 200 periods. The simulation results verified that the 0 proposed control plan can suppress the voltage -200 -400 fluctuations effectively. 5 400 ui 0 -5 uo 200 400 200 0 -200 0 -400 5 -200 0 -5 -400 200 0 0.05 0.1 0.15 0.2 0 Fig.9 - Output voltage waveforms when input -200 0 0.02 0.04 0.06 0.08 0.1 voltage fluctuations occur Fig.10 shows the simulation results of the output voltage waveforms when input voltage Fig.7 - Simulation results of (a)input voltage ui contains harmonic components. The total harmonic (b)input current ii (c)intermediate chopper voltage distortion (THD) in input voltage is 15.54%. By ucp (d)inductor current iL (e)output voltage uo using the proposed control method, the THD in output voltage is only 0.20%. The spectrum analysis is shown in Fig.6. The output voltage is a sinusoidal waveform and the voltage harmonic components are 150 100 highly reduced. The simulation results confirm that the commutation process is not affected by the harmonic voltage and the designed control strategy 50 can work effectively to eliminate the harmonic u(V) 0 (a) components. -50 400 -100 u i -150 u 0.023 0.023 0.023 0.0231 0.0231 0.0231 0.0231 o t(s) 200 150 100 0 50 u(V) 0 (b) -200 -50 -100 -400 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 -150 0.023 0.023 0.023 0.0231 0.0231 0.0231 0.0231 t(s) Fig.10 - Output voltage waveform when input Fig.8 - Voltage across S1 (a) without snubber voltage contains harmonic components circuits (b) with snubber circuits Fig.9 shows the simulation results of the output voltage waveforms when input voltage fluctuations occur. ui and uo are input voltage and output voltage respectively. At 0.04s, input voltage increases abruptly by 15% during 5 periods. At 0.08s, input ISSN: 1109-2734 214 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang 1.2 1 input voltage output voltage voltage THD 0.8 0.6 0.4 0.2 0 1 3 5 7 9 11 13 15 17 19 harmonic orders Fig.11 - Harmonic spectrum analysis of the input and output voltage 6 Experiment The digital signal processor (DSP) can implement with smaller size and lower cost than the general purpose microprocessor. Moreover, compared to the microcontroller, DSP has higher processing speed and more powerful ability in executing complex control algorithm. In experiment, the overall system is divided into two parts: the controller and the power circuit. The controller part includes the DSP running the proposed control Fig.12 - (a) Control signal of the bidirectional algorithms. The feedforward and feedback control switches (b) output voltage of AC chopper algorithm of the proposed voltage regulator is implemented using a DSPIC30f4011. Switching 70 period and duty ratio calculation are implemented in software. The PWM pulses are generated by the 60 PWM module in the DSP. Voltage signals are measured by using the analog digital converter 50 (ADC) module in DSP. The implementation of the voltage controllers and PWM pulse generation is performed in every switching period. The bilateral 40 switch consists of the IGBT and the fast recovery experiment diode rectifier. 10A/600V IGBT and 10A/600V fast 30 calculation recovery diodes are selected as the switching devices. These switches are operated at a fixed 20 switching frequency 40kHz and a dead time of 1 us. In experiment, the steady-state RMS value of the input voltage is 70V. When the duty ratio D is 10 0.2 0.4 0.6 0.8 1 0.6, the ideal output voltage should be Uo=0.6Ui. The PWM control signal is shown in Fig.12(a). The waveform of the chopper voltage ucp is shown in Fig.13 - the output voltage of experiment and Fig.12(b). The experiment results show that the calculation with different duty ratio input voltage is chopped into segment and the The input power factor is shown in Fig.14. voltage spikes across the switch are reduced. According to equation (14), the input power factor The RMS value of output voltage is 41.6V. The can be obtained with different duty ratio. The voltage error is caused by the voltage drop of the experiment results show that the lowest power switching devices and the power loss of the factor is 0.97. Compared to thyristor phase control converter. The output voltage with different duty circuit, the input power factor is improved. Thus, ratio is shown in Fig.13. the power line transmission loss caused by reactive ISSN: 1109-2734 215 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang power can be reduced. stable sinusoidal wave. The voltage fluctuations can The power transfer efficiency with different be suppressed and the output voltage is not duty ratio is shown in Fig.15. In this experiment, the influenced by the input voltage fluctuations. The highest power transfer efficiency can be achieved at proposed feedforward and feedback controller can 96.8%. The experiment results verify that the regulate the duty ratio and keep output voltage proposed voltage regulator has high power factor stable. and high efficiency. 1 0.98 calculation experiment 0.96 0.94 0.92 Fig.16 - output voltage waveform in experiment when input voltage fluctuations occur 0.9 0.2 0.4 0.6 0.8 1 7 Conclusion Fig.14 - input power factor characteristics of An improved topology of two switches AC experiment and calculation with different duty ratio chopper voltage regulator and the output voltage control strategy are proposed. The commutation strategy and the operation modes are investigated. The snubber circuit is added to reduce the voltage 1 spikes in dead-time period and ensure the safe commutation. The steady-state equivalent circuit 0.95 and the input power factor are derived through theoretical analysis. The output filter is designed R=40 and the parameter calculation method is also 0.9 R=100 presented. The proposed voltage regulator has high input power factor, high power transfer efficiency. 0.85 The feedforward and feedback control method is designed to keep output voltage stable. The input 0.8 voltage fluctuations can be suppressed. In addition, the harmonic components can also be eliminated. A 0.75 prototype is setup to test the performance. In experiment, the input power factor can be achieved to 0.99, and the power efficiency can reach 97.6%. 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 When input voltage fluctuations occur, the output voltage can be regulated stable. Simulation and Fig.15 - power transfer efficiency characteristics experiment results confirmed the validity of the When input voltage fluctuations occur, the proposed plan. waveforms of input and output voltage are shown in Fig.16. In this experiment, the RMS value of the steady-state input voltage is 70V and the RMS value References: of the reference output voltage is 50V. The [1] B.H. Kwon, Gang Youl Jeong, Novel Line experiment results show that the output voltage is Conditioner With Voltage Up/Down Capability, ISSN: 1109-2734 216 Issue 4, Volume 9, April 2010 Jin Nan, Tang Hou-Jun, Bai Liang-Yu, WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Geng Xin, Yang Xiao-Liang IEEE Transactions On Industrial Electronics, [13] J.H. Kim, B.D. Min, and B.H. Kwon, A PWM Vol.49, No.5, pp.1110-1119, 2002 Buck–Boost AC Chopper Solving the [2] S.M. Hietpas, M. Naden, Automatic voltage Commutation Problem, IEEE Transactions On regulator using an AC voltage-voltage Industrial Electronics, Vol. 45, No. 5, pp.832- converter, IEEE Transaction on Industry 835, 1998 Application, Vol.36, No.1, pp.33-38, 2000 [14] Shinyama T, Ueda A, and Torii A, AC chopper [3] Veszpremi K, Hunyar M., New application using four switches, Proceedings of Power fields of the PWM IGBT AC chopper, Eighth Conversion conference, pp.1056-1060, 2002 International Conference of Power Electronics [15] S. Polmai, E. Sugprajun, Experiment On and Variable Speed Drives, pp. 46-51, 2000 Instantaneous Value Voltage Control of a [4] Bodur H., Bakan A.F., Sarul M.H., Universal Single Phase AC Chopper, Proceedings of the motor speed control with current controlled IEEE Conference PCCON 07, pp.77-82 , 2007 PWM AC chopper by using a microcontroller, Proceedings of IEEE International Conference on Industrial Technology,Vol.2, pp. 394-398, 2000 [5] Sundareswaran K., Rajasekar N., Sreedevi V.T., Performance comparison of capacitor-run induction motors supplied from AC voltage regulator and SPWM AC chopper, IEEE Transactions on Industrial Electronics, Vol.53, pp.990-993, 2006 [6] Shinichiro Fujikura, Akiteru Ueda, and Akihiro Torii, Analysis of a Three-Phase Buck-Boost AC Chopper Controlled in Two Phases, Power Conversion Conference, pp.824-830, 2007 [7] Geraldo C. R. Sincero and Arnaldo José Perin, High Pressure Sodium Lamp High Power Factor Electronic Ballasts Using AC–AC Converters, IEEE Transactions On Power Electronics, 2007,Vol. 22, No. 3: 804-814 [8] Balci M.E., Hocaoglu M.H. Effects of Source Voltage Harmonic Distortion on Power Factor Compensation in Triac Controlled AC Chopper Circuits, International conference on PEDS, Vol. 2, pp. 1199–1204, Nov., 2005 [9] Nabil A. Ahmed, Kenji Amei, and Masaaki Sakui, A New Configuration of Single-Phase Symmetrical PWM AC Chopper Voltage Controller, IEEE Transactions On Industrial Electronics, Vol. 46, No. 5, pp.942-952, 1999 [10] N.A. Ahmed, Kenji Amei and Masaaki Sakui, Improved Circuit of AC Choppers for Single- Phase System, Proceedings of the IEEE Conference PCCON, Vol.2, pp. 907-912, 1997 [11] Takayuki Shinyama, Makoto Kawai, Akihiro Torii, Akiteru Ueda, Characteristic of an AC Chopper Circuit with LC Filters in the Input and Output Side, Electrical Engineering in Japan, Vol.155, No.2, pp.45-52, 2006 [12] B.H. Kwon, J.H.Youm, J.H. Choi, Automatic voltage regulator with fast dynamic speed, IEE Proceedings of Electrical Power Application, Vol.146, No.2, pp.201-207, 1999 ISSN: 1109-2734 217 Issue 4, Volume 9, April 2010

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