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International Journal of Advances in Science and Technology, Vol. 5, No.3, 2012 A High Voltage Gain Switched Inductor Multilevel Boost Converter for PV Applications P.GANESH KUMAR G. BALAJI M.Tech Student Scholar Asst Professor Department of Electrical and Electronics Engineering, Department of Electrical & Electronics Engineering, Gudlavalleru Engineering College; Gudlavalleru(M); Gudlavalleru Engineering College; Gudlavalleru(M); Krishna(Dt); A.P, India. Krishna(Dt); A.P, India e-mail: papisettiganesh@gmail.com e-mail: gutta_balaji@yahoo.co.in Abstract- In dc-to-dc conversion applications that require a The main multilevel converters’ applications are focused in large range of input and/ or output voltages, conventional high power motor drives, static VARs compensation, and PWM converter topologies must operate at extremely low duty other utility applications they are also suitable for FACTS ratios, which limits the operation to lower switching devices. They can also been applied to DC-DC conversion frequencies because of the minimum ON time of the switch. in low power, especially for automotive applications, and This is eliminated in a new class of single switch PWM converters featuring high voltage gain conversion ratios. In renewable energy systems. this paper presents a new single stage dc – dc boost converter topology with very large gain conversion ratio as a switched Renewable energy sources such as photovoltaic’s, fuel inductor multilevel boost converter (SIMLBC). It is a PWM- cell and wind energy generate their power at very low dc based dc- dc converter which combines the Switched Inductor voltage which is not suitable for generating the ac supply structures and the switching capacitor function to provide a with 110 or 220v directly. The conventional dc- dc with low very large output voltage with different output dc levels which dc conversion ratio is not suitable for these applications makes it suitable for multilevel inverter applications. The unless many of these sources are connected in series to proposed topology has only single switch like the conventional increase their net dc voltage. Unfortunately sometimes dc- dc converter which can be controlled in a very simple way. In addition to, two inductors, 2N+2 diodes, N is the number of connection of many renewable energy sources in series output dc voltage levels, and 2N-1 dc capacitors. A high decreases their efficiency. There are some proposed switching frequency is employed to decrease the size of these solutions for increasing the dc- dc gain conversion ratio of components and thus much increasing the dynamic dc converters. First solution is to use of cascaded of performance. Here we proposed a new topology of boost converters increase the conversion ratio which is a no- converter implemented by using PV cells; the system is solution in the today’s energy saving conscious world, as evaluated using Matlab/Simulink Platform. this procedure implies an overall efficiency equal to the product of the efficiencies of each circuit. The second Keywords- Switched Inductor Boost Converter (SIBC), Multilevel solution is to use the quadratic converters which can Boost Converter (MLBC), and Power Conditioning System (PCS), Photo-Voltaic (PV) System. somehow alleviate the efficiency problem but they many present voltage or current overstresses. I. INTRODUCTION In photovoltaic systems, solar energy is converted into Multilevel converters have attracted interest in power electrical energy by photovoltaic (PV) arrays. PV arrays are conversion, they already are a very important alternative in very popular since they are clean, inexhaustible and require high power applications [1] It has been shown that they are little maintenance. Photovoltaic systems require interfacing useful in virtually all power conversion processes such as power converters between the PV arrays and the load. ac-dc, dc-ac, dc-dc and ac-dc-ac Some of the advantages of multilevel converters against traditional topologies are: (i) A better solution is to use a dc- dc converter with steep low harmonic distortion, (ii) low voltage stress, (iii) low step- up conversion ratio. By looking to the literature there EMI noise, (iv) low switching frequency, (v) high are a less number of dc-dc converters with very high gain efficiency, (vi) ability to operate without magnetic conversion ratio. Two types of the dc – dc for high dc gain components. All these advantages make multilevel conversion ratio is switched inductor boost converter and converters one of the most important topics in power multilevel boost converter. This work proposes a new electronics, and industrial application research, and in some topology based on the two topologies that have a very high applications they can get modular topologies [2]. conversion ratio without scarifying its performance. The proposed system is suitable for utility applications such as ac modules. Distributed power supplies are expected to become increasingly prevalent in the near future, they September Issue Page 28 of 132 ISSN 2229 5216 International Journal of Advances in Science and Technology, Vol. 5, No.3, 2012 requires a power conditioning system (PCS) to control the frequency and voltage output from renewable energy sources. It is a must to transfer energy from these sources into utility grids at unity or near unity power factor. The system block diagram is shown of Fig.1. Fig. 2. The schematic diagram of SIMLBC Fig. 1. The block diagram of dc- ac PCS with dc-dc SIMLBC As mentioned these applications require a converter that The two operation modes of this topology are indicated in converts a small voltage to a high voltage so the converter Fig. 3 and 4. When the switch on, the two inductor is should have a high boosting ratio. One candidate is connected to the voltage source through Ds1 and Ds3. If transformer-isolated boost topologies, however these C 3 ’s voltage is smaller than C 1 ’s voltage then C 1 charging converters have low efficiency as the boosting ratio of the C 3 through diode and the switch as shown in Fig. 4. When transformer becomes higher. So this paper proposes a new the switch turns off, the diodes and will be reversed and the diodes D s1 and D s3 will be reversed and the diodes D s2 transformer–less high voltage gain converter and proposed and D 1 will turn on because the two inductors charge the system implemented by using the PV arrays. It is a switched capacitor C 1 until the voltage on the capacitor C 1 is equal to inductor multilevel boost converter as a high gain dc-dc the summation voltage on the source and the two inductors converter to feed any applications that require high dc voltage. After that, the diode D 3 turns on, thus the input voltage or to feed multilevel inverter that is used in ac source , the two inductors and capacitor C 3 charge the applications that requires low total harmonic distortions. capacitors C 1 + C 2 through it. When the voltage on the C 1 + C 2 is equal to the summation voltage on the input source, the voltage on the two inductors and the voltage on the II. THE PROPOSED TOPOLOGY SIMLBC capacitor C 3, then diode D 3 then turns off as shown in Fig. OPERATIONAL MODES 4. Fig.2. shows the schematic diagram of the proposed topology SIMLBC. It consists of two inductors, 2N+2 diodes; N is the number of the dc output voltage levels, and 2N-1 dc capacitors. Likewise, the operation of the proposed SIMLBC is almost same like the operation of the conventional boost converter since it has only single electronic switch. The main difference between the conventional boost converter and the SIMLBC is the input coil. In the SIMLBC, the coil has been replaced by two coils named a switched coil. Fig.3. Mode 1 switch is in ON state September Issue Page 29 of 132 ISSN 2229 5216 International Journal of Advances in Science and Technology, Vol. 5, No.3, 2012 Fig. 5. Conventional Boost Converter. But at the switched inductor multilevel boost converter the equation of the inductor on the ideal will be �������� = ������������ ���� + (������������ \2 − ����0 \2����)(1 − ����) (5) Fig. 4. Mode 2 switch is in OFF state. So the gain ratio of the new topology will be as follows: ����0 \������������ = ����(1 + ����)\1 − ���� (6) III. ANALYSIS STUDY OF THE PROPOSED SIMLBC Taking into account the ESR of the inductor for both the conventional boost converter and SIMLBC, equation (1) can be modified as follows: �������� = ����(������������ − ����1 ����1 ) + (1 − ����)(������������ − ����0 − ����1 ����1 ) = 0 Fig.3. shows the conventional boost converter that consists of the one inductor, one capacitor, one diode and one (7) switch. Equation (1) describes the average voltage of the inductor on the ideal conventional boost converter as Then from equations (4) and (7), the gain conversion ratio �������� = ����(������������ ) − (1 − ����)(������������ − ���� ) follows. will equal to ���� (1) ����0 \������������ = 1\1 − ���� + �������� (1 − ����)����0 (8) The steady state voltage on the capacitor the output voltage ����0 ����� = 1� 1 − ���� And for the SIMLBC, equations (5) and (6) will result in: �������� ���� is governed by equation 4: ����0 + (9) ����(1 + ����) ����0 (1 − ����) �������� ������������ = 1/(1-D) (2) The equation of the inductor current is obtained by equating From (8) and (9), the output voltage of the proposed topology is larger than the conventional boost converter ���������������� = ����0 /����0 the input and output powers and neglecting the losses as 2 follows. with N×(1+D) where N is the dc output voltage levels and D is the duty cycle. The design values for the inductors and �������� = ����0 /������������ ����0 2 capacitors of the SIMLBC can be found from the (3) conventional boost converter by replacing the voltage gain From (2) and (3) the inductor current is: conversion ratio as given in (10) and (11) below: �������� = ����0 /(1 − ����)����0 ����(1−����)2 ���� (4) 2����2 L= (10) ���� = ���������������� ���� �������� ∆�������� (11) September Issue Page 30 of 132 ISSN 2229 5216 International Journal of Advances in Science and Technology, Vol. 5, No.3, 2012 Thus the relation between input and output voltages is equal the cell generates charge carriers that originate an electric to the input voltage multiplied by the levels of the converter current if the cell is short circuited. multiplied by the (1+duty cycle) and divided on (1-duty cycle). The main advantages for this topology are the output voltage can be increased by increasing the levels of the SIMLBC by add a capacitors and diodes without changing the main circuit. Also, the voltage stress on the switch is smaller than the conventional boost converter. Again the dc gain conversion ratios of the SIMLBC, MLBC, SIBC, and the conventional boost converter can be summarized in the Fig. 6: Equivalent Circuit of a PV Device including the series and parallel following equations. The dc gain conversion ratio of the Resistances. = MLBC [5] is as follows: ����0 ���� The equivalent circuit of PV cell is shown in Fig. 6. In the ������������ 1−���� (12) above diagram the PV cell is represented by a current source in parallel with diode. Rs and Rp represent series and = The dc gain conversion ratio of the SIBC [4] is as in (13) parallel resistance respectively. The output current and ����0 (1+����) voltage from PV cell are represented by I and V ������������ 1−���� (13) Equations (2), (6), (12), and (13) describe the dc gain conversion ratio of the conventional boost converter, SIMLBC, MLBC, and SIBC, respectively. It can be noted that the dc gain conversion ratio of the SIMLBC is the highest values among them. This is the main advantage of this new topology. Fig. 6 gives a comparison among the four aforementioned topologies in the ideal case at different Fig. 7. V-I Characteristic of PV Cell duty cycles. It can be clearly noticed that from this figure The I-V Characteristics of PV cell [7] is shown in Fig.7. that for low duty cycle the dc gain conversion ratios of these The net cell current I is composed of the light- generated converters have no much difference. However, for duty current Ipv and the diode current Id cycle greater than 0.5, a very big difference can be noticed ���� = ������������ − �������� among these topologies. Also the dc gain conversion ratio of the SIMLBC becomes much higher for duty cycle greater (14) than 0.5 compared to the other three topologies. So it is preferred to operate this converter for duty cycle larger than Where 50% and smaller than 90% for getting on higher dc gain conversion ratio. The second advantage of the SIMLBC is Id � Io exp�qV⁄akT� the voltage stress in the components due to using the Io = leakage current of the diode multilevel behavior. The stress voltage depends on the level q= electron charge of the SIMLBC because the voltage on the switch when it is k = Boltzmann constant in the off state equals to the output voltage divided by the T= temperature of pn junction number of levels of the converter. a= diode ideality constant IV. ABOUT PHOTO VOLTAIC SYSTEMS AND The basic equation (1) of the pv cell does not represent the MPPT ALGORITHM I-V characteristic of a practical PV array. Practical arrays are composed of several connected PV cells and the A photovoltaic (PV) system directly converts sunlight into observation of the characteristic at the terminals of the PV electricity. The basic device of a PV system is the PV cell. array requires the inclusion of additional parameters to the Cells may be grouped to form panels or arrays. The voltage basic equation. ���� = ������������ − �exp ����� + � − 1� − ������������ ����+������������ and current available at the terminals of a PV device may ������������ ���� ���� directly feed small loads such as lighting systems and dc motors. [7] A photovoltaic cell is basically a semiconductor (15) �������� = ����������������/���� diode whose p–n junction is exposed to light. Photovoltaic Where cells are made of several types of semiconductors using different manufacturing processes. The incidence of light on September Issue Page 31 of 132 ISSN 2229 5216 International Journal of Advances in Science and Technology, Vol. 5, No.3, 2012 Is the thermal voltage of the array with Ns cells connected in series. Cells connected in series provide greater output voltages. The I-V characteristic of a practical PV cell with maximum power point (MPP), Short circuit current (Isc) and Open circuit voltage (Voc) is shown in Fig. 8. The MPP represents the point at which maximum power is obtained. Fig. 8. I-V Characteristic of Practical PV Module Fig. 10 Output Voltage ,Input Voltage, Duty cycle Vmp and Imp are voltage and current at MPP respectively. The output from PV cell is not the same throughout the day; Fig 10 shows the Output voltage & input voltage and duty it varies with varying temperature and insulation (amount of cycle of the proposed switched inductor multilevel boost radiation). Hence with varying temperature and insolation converter. maximum power should be tracked so as to achieve the efficient operation of PV system. V. MATLAB/SIMULINK MODELLING AND SIMULATION RESULTS Here the simulation is carried out by three cases 1. Proposed switched inductor multilevel boost converter 2. Closed loop operation of proposed switched inductor multilevel boost converter 3. Implementation of proposed switched inductor multilevel boost converter by using PV arrays applied to grid. Case 1: Proposed switched inductor multilevel boost Fig .11. Input Current , Duty Cycle converter: Fig 11 shows the Input Current & Duty Cycle of the proposed switched inductor multilevel boost converter. Fig.9. Matlab/Simulink modeling of proposed switched inductor multilevel boost converter Fig.9 Shows the Matlab/Simulink modeling of proposed switched inductor multilevel boost converter. Fig.12. Voltage across switch September Issue Page 32 of 132 ISSN 2229 5216 International Journal of Advances in Science and Technology, Vol. 5, No.3, 2012 Case 2:. Closed loop operation of proposed switched Fig 15 shows the Matlab/Simulink modeling of proposed inductor multilevel boost converter switched inductor multilevel boost converter by using PV arrays applied to grid. Fig.16. Output Voltage Fig.13. Matlab/Simulink modeling of Closed loop operation of proposed switched inductor multilevel boost converter Fig.14. Output Voltage of Closed loop operation of proposed switched Fig.17. Inverter Output Voltage inductor multilevel boost converter Fig 16, 17 shows the converter output voltage and output voltage of the inverter; we convert DC Voltage to AC by Case 3: Implementation of proposed switched inductor using Interfacing Inverter and applied to Grid. multilevel boost converter by using PV arrays applied to grid. Fig.18. Grid Voltage Fig.15. Matlab/Simulink modeling of proposed switched inductor multilevel boost converter by using PV arrays applied to grid. September Issue Page 33 of 132 ISSN 2229 5216 International Journal of Advances in Science and Technology, Vol. 5, No.3, 2012 V CONCLUSION AUTHORS PROFILE This paper proposed a new dc-dc converter topology. The P GANESH KUMAR received his B.Tech degree major advantages for this topology are high boosting ratio from J.N.T.University, Hyderabad in the year 2009. without using transformer. The voltage stress on the switch At present he is pursuing his M.Tech degree is smaller than the voltage stress on the switch in Gudlavalleru Engineering College, Gudlavalleru, with the specialization of Power Electronics & Electrical conventional boost converter. Also the efficiency of this Drives. His areas of interest are Electrical Machines converter has been found that is large and the output voltage and Power Electronics, Electrical Circuits. can be increased by increasing a level of this topology by increasing a number of capacitors and diodes without changing the main circuit and same proposed converter is applied to Grid by using interfacing inverter. BALAJI GUTTA has received his B.Tech degree REFERENCES from Gudlavalleru Engineering college, Gudlavalleru under J.N.T.University, Hyderabad in the year 2002. [1] “Power Electronics Handbook” M.H. Rashid, Academic Press, M.Tech degree with the specialization of Electrical 2001. Drives and Control from Pondicherry Engineering College in the year 2006. At present he is working as [2] D. Maksimovic, and S. Cuk, "Switching converters with wide DC an Assistant Professor in Gudlavalleru Engineering conversion range, " IEEE Transactions on Power Electronics, Vol. 6, pp. college, Gudlavalleru. His areas of interest are 149-157, Jan. 1991. Advanced Control Systems, Nonlinear control Systems, Control Systems, Network Analysis, Electrical Machines and Power Electronics. [3] V. Paceco, A. Nascimento, V. Farias, J. Viera, L. Freitas, "A quadratic buck converter with lossless commutation", IEEE Transactions on Industrial Electronics, Vol. 47, pp. 264-271, Apr. 2001. [4] Boris Axelrod, Yefim Berkovich, and Adrian Ioinovici “Switched Capacitor/Switched Inductor Structures for Getting Transformerless Hybrid DC–DC PWM Converters” IEEE Transactions on circuits and systems-I, Regular papers, Vol.. 55, NO. 2, March 2008. [5] Julio C. Rosas-Caro, Juan M. Ramírez, Pedro Martín García-Vite "Novel DC-DC Multilevel Boost Converter." Proceeding of IEEE Power Electronics Specialists Conference, 2008. [6] Mahrous El-Sayed Ahmed, Mostafa Mousa, Mohamed Orabi “Development of High Gain and Efficiency Photovoltaic System Using Multilevel Boost Converter Topology” 2nd International Symposium on Power Electronics for Distributed Generation Systems (PEDG2010). [7] www.powersimtech.com. September Issue Page 34 of 132 ISSN 2229 5216