SOFT-SWITCHING INTERLEAVED BOOST CONVERTER WITH HIGHT VOLTAGE GAIN Ranoyca N. A. L. Silva 1, Gustavo A. L. Henn 2, Paulo P. Praça 3, Raphael A. da Câmara 4, Demercil S. Oliveira Jr 5, Luiz H. S. C. Barreto 6 (IEEE Member) Federal University of Ceará Energy and Control Processing Group GPEC ZIP CODE - 60455-760, Fortaleza CE Brazil ranoyca@click21.com.br 1, guhenn@terra.com.br 2, paulopp@dee.ufc.br 3, raphaelpur@gmail.com 4, demercil@dee.ufc.br 5, lbarreto@dee.ufc.br 6 Abstract In this paper a soft-switching interleaved boost converter with high voltage gain is presented. The high voltage gain converter is far suitable for applications where a high step-up voltage is required, as in some renewable energy systems, which use, for example, photovoltaic panels and/or fuel cells. Besides, in order to guarantee small switching losses and, consequently, a high efficiency, a non-dissipative soft-switching cell with auxiliary commutation circuit is used. Thus, a large stepup voltage, low switching stress, small switching losses, and high efficiency are expected from this topology. In order to verify its effectiveness, experimental waveforms from the high voltage gain converter operating with hard-switching and soft-switching are compared. Also, waveforms from the soft-switching cell are presented and analyzed. Theoretical analysis, operation principle and topology details are also presented and analyzed. Keywords - Soft-switching, Boost Converter, Nondissipative Cells. I. INTRODUCTION Renewable energy systems are being more and more common to help providing electric energy. However, conventional photovoltaic panels and fuel cells produce low voltage levels, requiring a large step-up voltage DC/DC converter to feed conventional 110 V RMS AC systems. The conventional boost converter is not suitable for this purpose because, to obtain such high gain, it would operate with duty cycle greater than 0.95, which is very hard to achieve due to operational limitations. To solve this drawback, some topologies were suggested, as in [1-13]. In [3] and [4], the use of an interleaved boost converter associated with an isolated transformer was introduced, using a high frequency AC link. Despite of the good performance, this topology uses three magnetic cores. In [5], the converter presents low input current ripple and low voltage stress across the switches. However, high current flows through the series capacitors at high power levels. In [6-8], converters with high static gain based on the boostflyback topology are introduced, which presents low voltage stress across the switches, but the input current is pulsed, as it needs an LC input filter. The step-up switching-mode converter with high voltage gain using a switched-capacitor circuit was proposed in [9]. This idea is only adequate for low power converters as it results in a high voltage stress across the switches and many capacitors are necessary. In [10-12] the three-state switching cell is shown. In [12] a voltage doubler rectifier is employed as the output stage of an interleaved boost converter with coupled inductors. The converter presented in [13] has some advantages compared to the others: possibility to operate in large voltage range, high efficiency, and high power capability. Figure 1 shows the high voltage gain boost converter from [13]. It can be seen from Figure 1 that the number of semiconductor devices is the same as in the traditional interleaved boost arrangement, though two coupled inductors L 1 and L 2 are added, resulting in higher output voltage. The main drawback of this topology is the hard switching mode, which causes power losses. Because of this drawback, it is important to analyze the most suitable soft-switching cell to reduce the power losses in both switches S 1 and S 2 [14-20]. The soft-switching cell proposed in [20] presents some advantages compared to the others: it is non-dissipative, uses auxiliary commutation circuits, and do not present load limitations, as it can deal with high nominal power systems. Fig. 1. High voltage gain boost topology.
Thus, the topology presented in Figure 1 will be adapted to work with a non-dissipative snubber, as seen in Figure 2. Its operation and main waveforms will be detailed and discussed in this paper. Fig. 3. First Stage Fig. 2. Converter with soft-switching cells. II. OPERATION PRINCIPLE This section presents the operation principle from the high voltage gain boost converter with the commutation cells. For the theoretical analysis, it will be considered that the input voltage (Vi) and output current (Io) are ripple free and all devices are ideal. First Stage [t 0 t 1 ] - Prior to the first stage S 1 and D 3 were turned-on, L b1 is charged, and V Cr1 and V Cr2 are equal to zero. This stage (Figure 3) begins when S a2 and D r2 are turned-on in ZCS mode. During this stage, the resonant current through the inductor (I Lr2 ) increases linearly from zero to the input current I Lb2. This stage ends when I Lr2 = I Lb2. Second Stage [t 1 t 2 ] - During this stage (Figure 4), I Lr2 and the resonant capacitors C r3 and C r4 starts to resonate, discharging C r3 and charging C r4. This stage ends when V Cr3 reaches zero. Third Stage [t 2 t 3 ] - During this stage (Figure 5), I Lr2 and C r4 resonate. This stage ends when I Lr2 reaches zero. At this stage, S 2 is turned-on in ZVS mode. Fourth Stage [t 3 t 4 ] - After I Lr2 reaches zero, the auxiliary switch S a2 is turned-off in ZCS mode. The switch S 2 and S 1 remains turned on. The energy keeps being stored in L B1, without being transferred to the load and L B2 starts to be charged. Besides, C r4 is linearly discharged to zero by the current I Lb2. As the voltage through C r1 is zero, the switch S 1 will be turned-off in ZVS mode, ending this stage. Fifth Stage [t 4 t 5 ] - At t 4, as V Cr4 is zero, the diode D 4 is turned-on in ZVS mode. As I Lb1 cannot reach zero instantly, it will flow through C r1, until V Cr1 reaches V Cf. Thus, the diode D 3 turns-off in ZVS mode. This stage, represented in Figure 7, ends when D b1 turns-on in ZVS mode. Sixth Stage [t 5 t 6 ] - As D b1 starts to conduct, the energy previously stored in the inductor L B1 is now transferred to the capacitor C F1 through the circuit showed in Figure 8. Figures 9 to 14 present the next stages, which are similar to the six stages presented above, although stages 7 to 12 describe the principle operation for the boost switch S 1 and for its soft-switching cell (D r1, C r1, C r2, L r1, and S a1 ). Fig. 4. Second Stage Fig. 5. Third Stage Fig. 6. Fourth Stage Fig. 7. Fifth Stage
Fig. 8. Sixth Stage Fig. 13. Eleventh Stage Fig. 9. Seventh Stage Fig. 14. Twelfth Stage III. SISTEM SIMULATION AND EXPERIMENTAL RESULTS Fig. 10. Eighth Stage Fig. 11. Ninth Stage Fig. 12. Tenth Stage This topic presents the simulation (figures 15 and 16), and experimental (figures 17 to 21) results from the nondissipative snubber commutation cell applied to the high voltage gain converter. The system has an input voltage of 28 Vdc and output voltage of 180 Vdc, making possible to feed a 110 V RMS AC system. The prototype was assembled to supply a linear 500 W load. Figure 15 presents the voltage and the current during the turn-on period through the switch S1, while figure 16 presents the voltage and the current during the turn-on period through the auxiliary switch Sa1. It must be observed from these figures that the switch S1 start to conduct in ZVS mode, while the auxiliary switch Sa1 operates in ZCS mode. The same waveforms are valid to switches S2 and Sa2. It is also important to emphasize that the same occurs during the turn-off period (ZVS for S1 and S2, and ZCS for Sa1 and Sa2). Figures 17 and 18 present, respectively, the experimental results from the input and output voltage and current. From them, it can be verified the effectiveness from the converter, which highly step-up the input voltage to the desired output voltage. Figure 19 presents the voltage through each output capacitor, which are equilibrated. Measured Vcf1 is 52.5V, while Vcf2 is 53.9V, and Vcf is 60,3V. Figure 20 presents the voltage and the current waveforms through switch S 1. It can be observed from that figure that the main switch only starts to conduct in ZVS mode, as expected from simulation results. It is important to emphasize that the voltage stress through that switch is only Vout/3. Figure 21 presents the voltage and the current waveforms through switch S a1. It can be noticed that the auxiliary switch
only starts to conduct in ZCS mode as expected from simulation results, which verifies the non-dissipative characteristic from the used soft-switching cell. Fig. 19. Vcf1, Vcf2 e Vcf Fig. 15. V and I through S1 during the turn-on period (simulated) Fig. 16. V and I through Sa1 during the turn-on period (simulated) Fig. 20. V and I through S1 during the turn-on period. Fig. 17. Input voltage and current Fig. 21. V and I through Sa1 during the turn-on period IV. CONCLUSIONS Fig. 18. Output voltage and current Interleaved boost converter with high voltage gain and non-dissipative soft-switching snubber cell was presented. The main advantages of the topology are: low switching losses, high efficiency, and the converter s suitability in applications where large voltage step-up is demanded, such as renewable energy systems. The model validation from the high voltage gain boost through experimental results is presented, as the experimental results from the non-dissipative snubber cell, verifying the expected characteristics from the converter.
ACKNOWLEDGEMENT To the FUNCAP that supports the technologic development of Ceara s state, and to the GPEC members, for the friendship and diary support and knowledge exchange. REFERENCES [1] Qun Zhao, Fengfeng Tao, Yougxaun Hu, and Fred C. Lee, DC/DC Converters Using Magnetic Switches, IEEE Applied Power Electronics Conference and Exposition, 2001, APEC2001, Vol.2, pp. 946-952, March 2001. [2] Qun Zhao and Fred C. Lee. High-Efficiency, High Step-Up DC-DC Converters, in IEEE Transactions on Power Electronics, vol. 18, no. 1, pp. 65-73, January 2003. [3] Yungtaek Jang and Milan M. Jovanovic. A New Two- Inductor Boost Converter with Auxiliary Transformer, in IEEE Transactions on Power Electronics, vol. 19, no. 1, pp. 169-175, January 2004. [4] P.J. Wolfs, A Current-Sourced DC-DC Converter Derived via the Duality Principle from the Half-Bridge Converter IEEE Transactions on Industrial Electronics, Vol. 40, No. 1, pp. 139-144, February 1993. [5] Roger Gules, L. Lopes Pfitscher, and L. Claudio Franco. An Interleaved Boost DC-DC Converter with Large Conversion Ratio, in IEEE International Symposium on Power Electronics, 2003. ISIE 03, Vol.1, 9-12 June 2003, pp. 411-416. [6] K. C. Tseng and T. J. Liang, Novel high-efficiency step-up converter, in IEE Proc. Electr. Power Appl., Vol. 151, No.2, March 2004, pp. 182-190. [7] R. J. Wai and R. Y. Duan, High-efficiency DC/DC converter with high voltage gain, in IEE Proc. Electr. Power Appl., Vol. 152, No.4, July 2005, pp. 793-802. [8] J. W. Baek. M. H. Ryoo, T. J. Kim, D. W. Yoo, and J. S. Kim, High Boost Converter Using Voltage Multiplier, in IEEE Industrial Electronics Conference, 2005, pp.567-572. [9] O. Abutbul, A. Gherlitz, Y. Berkovich, and A. Ioinovici, Step-Up Switching-Mode Converter with High Voltage Gain Using a Switched-Capacitor Circuit, in IEEE Transactions on Circuits and Systems I:Fundamental Theory and Applications, Vol. 50, No.8, August 2003, pp.1098-1102. [10] G. V. Torrico Bascopé, and Ivo Barbi. Generation of a Family of Non-Isolated DC-DC PWM Converters Using New Three- State Switching Cells, in IEEE Power Electronic Specialists Conference, 2000, PESC 00, Vol.2, 18-23 June 2000, pp. 858-863. [11] G. V. T. Bascopé, R. P. T. Bascopé, D. S Oliveira JR, S. A Vasconcelos, F. L. M. Antunes, C. G. C. Branco. A High Step-UP Converter Based on Three-State Switching Cell. In: International Symposium on Industrial Electronics 2006, 2006, Montréal, Québec, Canada. ISIE 2006, 2006. p. 998-1003. [12] D. S. Oliveira Jr., R. P. T. Bascopé, C. E. A. Silva Proposal of a New High Step-Up Converter for UPS Applications. In: International Symposium on Industrial Electronics, 2006, Montreal. IEEE Catalog Number 06TH8892. [13] E. A. S Silva, D. S. Oliveira, T. A. M Oliveira, F. L. Tofoli, A Novel Interleaved Boost Converter With High Voltage Gain For UPS Applications, Congresso Brasileiro de Eletrônica de Potência COBEP 2007, Blumenau, SC, Brazil, Unique vol., CD-ROM. [14] C. M. Wang, C. H. Su, C. Y. Ho, and K. L. Fang, A Novel ZVS-PWM Single-Phase Inverter Using a Voltage Clamp ZVS Boost DC Link, Industrial Electronics and Applications, pp. 309-313, May 2007. [15] X. Wu, J. Zhang, X. Ye, Z. Qian A family of non-isolated ZVS DC-DC converter based on a new active clamp cell, Industrial Electronics Society, pp. 592-597, Nov. 2005. [16] C. M. Wang, A New Family of Zero-Current-Switching (ZCS) PWM Converters in: Power Electronics Specialists Conference, 1999. PESC 99. 30th Annual IEEE, vol. 1, pp. 451-456, Aug 1999. [17] W. Fan, G. Stojcic Simple zero voltage switching full-bridge DC bus converters in: Applied Power Electronics Conference and Exposition, 2005. APEC 2005. Twentieth Annual IEEE, vol. 3, pp 1611-1617, March 2005. [18] L. Yuanyuan, Q. Wenlong, M. Gang The ZVS Condition Analysis of a Novel Soft Switching Bidirectional DC/DC Converter in: TENCON 2006. 2006 IEEE Region 10 Conference pp. 1-4, Nov. 2006. [19] BARRETO, L. H. S. C. ; COELHO, E. A. A. ; FARIAS, V. J. ; de OLIVEIRA, J. C. ; de FREITAS, L. C ; Vieira, J. B. Jr. A Quasi-Resonant Quadratic Boost Converter Using a Single Resonant Network. IEEE Transactions on Industrial Electronics, v. 52, n. 2, p. 552-557, 2005. [20] L.H.S.C. Barreto, A. A. Pereira, V.J. Farias, L.C. de Freitas, J. B. Vieira Jr, A Boost Converter Associated With a New Non- Dissipative Snubber. Applied Power Electronics Conference and Exposition - APEC98, vol. 2, pp. 1077-1083, Feb. 1998. BIOGRAPHIES Ranoyca Nayana Alencar Leão e Silva graduated (2006) in electronic engineering from University of Fortaleza, Brazil. Nowadays studies the master course in electrical engineering from Federal University of Ceará, Brazil. Her employment experience and fields of interest included power electronics. Gustavo Alves de Lima Henn has graduation (2006) and master course (2008) in electrical engineering from Federal University of Ceará, Brazil. His employment experience and fields of interest included power electronics and photovoltaic energy. At the moment studies the doctor course in electrical engineering from Federal University of Ceará, Brazil. Paulo Peixoto Praça graduated (2003) in electronic engineering from University of Fortaleza, Brazil, and has concluded the master course in Power electronics from Federal University of Ceará. At the moment studies the doctor course in electrical engineering from Federal University of Ceará, Brazil. Raphael Amaral da Câmara has graduation (2005) and master course (2008) in electrical engineering from Federal University of Ceará, Brazil. His employment experience and fields of interest included power electronics and static converters for UPS applications. At the moment studies the doctor course in electrical engineering from Federal University of Ceará, Brazil. Prof. Demercil de Souza Oliveira Júnior, Dr. has graduation (1999) and master course (2001) in electrical engineering from Federal University of Uberlândia, Brazil, and doctor course (2004) from Federal University of Santa Catarina, Brazil. His employment experience and fields of interest included power electronics, soft-switching, wind energy systems, DC/DC converters, etc. At the moment teaches in Federal University of Ceará, Brazil, and is reviser from IEEE Transactions on Industrial Electronics and IEEE Transactions on Power Electronics. Prof. Luiz Henrique Silva Colado Barreto, Dr. He received the B. S. degree in Electrical Engineering from Universidade Federal de Mato Grosso, Brazil, in 1997 and the M. S. and Ph.D. degrees from the Universidade Federal de Uberlândia, Brazil, in 1999 and 2003 respectively. Since June 2003, he has been with the Electrical Engineering Department, Universidade Federal do Ceará, Brazil, where he is a Professor of Electrical Engineering. His research interest areas include high-frequency power conversion, modeling and control of converters, power factor correction circuits, new converters topologies, UPS system and fuel cell. Dr. Barreto is member of the IEEE Power Electronics Society and Industrial Application Society and the Brazilian Power Electronics Society (SOBRAEP).