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Analysis and Implementation of a DC-DC Converter for Hybrid Power Supplies Systems
Analysis and Implementation of a DC-DC Converter for Hybrid Power Supplies Systems
Journal of Power Electronics. 2015. Nov, 15(6): 1438-1445
Copyright © 2015, The Korean Institute Of Power Electronics
  • Received : March 14, 2015
  • Accepted : May 18, 2015
  • Published : November 20, 2015
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About the Authors
Lung-Sheng Yang
Department of Electrical Engineering, Far East University, Tainan City, Taiwan
yanglungsheng@yahoo.com.tw
Chia-Ching Lin
Department of Electrical Engineering, Far East University, Tainan City, Taiwan

Abstract
new DC-DC power converter is researched for renewable energy and battery hybrid power supplies systems in this paper. At the charging mode, a renewable energy source provides energy to charge a battery via the proposed converter. The operating principle of the proposed converter is the same as the conventional DC-DC buck converter. At the discharging mode, the battery releases its energy to the DC bus via the proposed converter. The proposed converter is a non-isolated high step-up DC-DC converter. The coupled-inductor technique is used to achieve a high step-up voltage gain by adjusting the turns ratio. Moreover, the leakage-inductor energies of the primary and secondary windings can be recycled. Thus, the conversion efficiency can be improved. Therefore, only one power converter is utilized at the charging or discharging modes. Finally, a prototype circuit is implemented to verify the performance of the proposed converter.
Keywords
I. INTRODUCTION
The use of the fossil fuels causes environmental pollution and ecological problems. In addition, carbon-dioxide emissions result in global warming. Therefore, the development and application of renewable energy sources has become very important [1] - [10] . Renewable energies include wind power, solar power, ocean energy, hydrogen energy, hydro energy and so on. Fig. 1 (a) shows the conventional renewable energy and battery hybrid power supply system. It can be seen that the battery is charged from a renewable energy source via two converters [11] - [17] . Therefore, the conventional hybrid power supply system results in energy waste. For this reason, this paper presents a new DC-DC converter for three-port renewable energy and battery hybrid power supplies systems, as shown in Fig. 1 (b). It can be seen that the battery is only via one converter at the charging or discharging mode. Fig. 2 shows the circuit configuration of the proposed converter. The pulse-width modulation (PWM) technique is used for the proposed converter. At the charging mode, the renewable energy source provides its energy to charge the battery via the proposed converter. Here the proposed converter is a conventional DC-DC buck converter [18] , [19] . At the discharging mode, the battery releases its energy to the DC bus via the proposed converter. Meanwhile, this converter is a non-isolated high step-up DC-DC converter [20] . The coupled-inductor technique is used to achieve a high step-up voltage gain by adjusting the turns ratio. Moreover, the leakage-inductor energies of the primary and secondary windings can be recycled. Thus, only one power converter is utilized at the charging and discharging modes. The operating principles and steady-state analyses will be described in the following sections for the charging and discharging modes.
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Renewable energy and battery hybrid power supplies system. (a) Conventional type, (b) Three-port type.
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Circuit configuration of proposed DC-DC converter.
In order to analyze the steady-state characteristics of the proposed converter, some conditions are assumed: (1) Because the capacitors C 1 , CB , and Cbus are sufficiently large, the voltages across these capacitors can be treated as constant during each switching period. (2) The ON-state resistance of the switches, the forward voltage drop of the diodes, and the equivalent series resistances of the coupled inductor and capacitors are ignored.
II. CHARGING MODE
When the proposed converter is operated in the charging mode, the primary winding of the coupled inductor is used for a general inductor. The equivalent circuit of the proposed converter at the charging mode is shown in Fig. 3 , where RB is the equivalent load for the battery. The PWM technique is used to control switch S 1 . Switch S 2 is used for the synchronous rectifier. Fig. 4 shows typical waveforms of the proposed converter with the continuous conduction mode (CCM) operation at the charging mode. The operating principles and steady-state analysis are described as follows:
1) Mode 1: During this time interval [ t 0 , t 1 ], switch S 1 is turned on and switch S 2 is turned off. The current flow path is shown in Fig. 5 (a). The renewable-energy source Vin supplies its energy to for the coupled inductor Lm , capacitor CB , and load RB . Meantime, the coupled inductor Lm stores its energy. Thus, the current iLm is increased. The voltage across the coupled inductor Lm is given by:
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2) Mode 2: During this time interval [t 1 , t 2 ], switch S 1 is turned off and switch S 2 is turned on. The current flow path is shown in Fig. 5 (b). Meanwhile, switch S 2 is utilized for a synchronous rectifier. The energy stored in the coupled inductor L m is released to the capacitor C B and load R B . The voltage across the coupled inductor L m is derived as:
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By using the voltage-second balance principle on the coupled inductor Lm , the following equation is obtained:
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Substituting (1) and (2) into (3), the voltage gain in the charging mode is found to be:
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When the proposed converter is operated in the boundary conduction mode (BCM), typical waveforms are shown in Fig. 6 . Thus, the peak value of the coupled-inductor current is written as:
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By utilizing the ampere-second balance principle on the capacitor CB , the following equation can be expressed as:
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From (6), the peak value of the coupled-inductor current can be rewritten as:
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Then, the normalized inductor time constant is defined as:
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Substituting (4), (5), and (8) into (7), the boundary normalized inductor time constant is given by:
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If τ Lm1 is larger than τ Lm1,B , the proposed converter is operated in the CCM at the charging mode.
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Equivalent circuit of proposed converter at charging mode.
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Some typical waveforms of proposed converter with CCM operation at charging mode.
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Current flow path of proposed converter at charging mode. (a) Mode 1. (b) Mode 2.
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Some waveforms of proposed converter with BCM operation at charging mode.
III. DISCHARGING MODE
The equivalent circuit of the proposed converter at the discharging mode is shown in Fig. 7 , where RL is the equivalent load for the DC bus. The PWM technique is used to control switch S 2 . Switch S 1 is turned off at the discharging mode. Fig. 8 shows typical waveforms of the proposed converter with the CCM operation at the discharging mode. The operating principles and steady-state analysis are described as follows:
1) Mode 1: During this time interval [ t 0 , t 1 ], switch S 2 is turned on. The current flow path is shown in Fig. 9 (a). The energy of the battery is released to the magnetizing inductor Lm and primary leakage inductor L k1 . Thus, the currents iLm and i Lk1 are increased. The secondary leakage inductor L k2 , secondary winding N 2 , capacitor C 1 , and battery are in series to release their energies for the load RL . The energy of the capacitor Cbus is also provided to the load RL . Therefore, the current i Lk2 decreases. At i Lk2 = 0, the energy stored in the leakage inductor L k2 is completely recycled to the load RL .
2) Mode 2: During this time interval [t 1 , t 2 ], switch S 2 is still turned on. The current flow path is shown in Fig. 9 (b). The energy of the battery is still released to the magnetizing inductor L m and primary leakage inductor L k1 . The energy of the capacitor C bus is provided to the load R L .
3) Mode 3: During this time interval [t 2 , t 3 ], switch S 2 is turned off. The current flow path is shown in Fig. 9 (c). The energies stored in the magnetizing inductor L m and primary leakage inductor L k1 are released the capacitor C 1 . Thus, the currents i Lm and i Lk1 are decreased. The secondary winding N 2 , capacitor C 1 , and battery are in series to release their energies for the leakage inductor L k2 , capacitor C bus , and load R L . Therefore, the current i Lk2 is increased. At i Lk1 = 0, the energy stored in the leakage inductor L k1 is completely recycled to the capacitor C 1 .
4) Mode 4: During this time interval [t 3 , t 4 ], switch S 2 is still turned off. The current flow path is shown in Fig. 9 (d). The secondary leakage inductor L k2 , secondary winding N 2 , capacitor C 1 , and battery are in series to release their energies for the capacitor C bus and load R L . Therefore, the currents i Lm and i Lk2 are decreased.
When switch S 2 is turned on, the following equation can be represented as:
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Thus:
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where the turns ratio of the coupled inductor n = N 2 / N 1 , and the coupled coefficient k = Lm /( Lm + L k1 ).
From the operating principle, it is known that the energy stored in the primary leakage inductor L k1 is recycled to the capacitor C 1 . By using the ampere-second balance principle on the capacitor C 1 , the released time duration of the primary leakage-inductor energy can be expressed as [20] :
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By utilizing the voltage-second balance principle on the primary leakage inductor L k1 and magnetizing inductor Lm , the following equations can be obtained:
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where v Lk1(tr) is the voltage across the primary leakage inductor L k1 during the time duration [ t 2 , t 3 ] and the voltage v N1(OFF) across the magnetizing inductor Lm during the time duration [ t 2 , t 4 ].
Substituting (11) and (14) into (15), yields:
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By substituting (12) into (16), it is possible to derive:
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From Fig. 9 (c), the following equation can be obtained:
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Substituting (17) and (18) into (19), the voltage across the capacitor C 1 is written as follows:
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During the switch S 2 OFF-period, the following voltage equation is found as:
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Therefore:
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Using the voltage-second balance principle on the secondary winding of the coupled inductor N 2 , the equation can be represented as:
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Substituting (13), (20), and (22) into (23), the voltage gain can be found as follows:
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At k = 1, equation (24) is rewritten as:
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The voltage gain with parasitic components is analyzed as follows. In order to simplify the analysis, the leakage inductors of the coupled inductor are neglected. The equivalent circuit is shown in Fig. 10 . r N1 and r N2 represent the equivalent series resistances (ESR) of the primary and secondary windings of the coupled inductor. V FD2 and r D2 are the ON-state forward voltage drop and resistance of D 2 . r S2 denotes the ON-state resistance of S 2 .
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Equivalent circuit of proposed converter at discharging mode.
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Some typical waveforms of proposed converter with CCM operation at discharging mode.
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Current flow path of proposed converter at discharging mode. (a) Mode1. (b) Mode 2. (c) Mode 3. (d) Mode 4.
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Equivalent circuit including ESR of coupled inductor, ON-state forward voltage drop and resistance of diodes, and ON-state resistance of switch. (a) S2 ON. (b) S2 OFF.
When switch S 2 is turned on, the equivalent circuit is shown in Fig. 10 (a). The average values of ibus and v N1 are written as:
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When switch S 2 is turned off, the equivalent circuit is shown in Fig. 10 (b). The average values of ibus and v N1 are found as:
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Since the leakage inductors of the coupled inductor are neglected, the coupling coefficient k is equal to 1. From (20), the voltage V c1 can be rewritten as:
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Substituting (30) into (29), yields:
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By using the ampere-second balance principle on Cbus , the following equations are obtained as:
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Substituting (26) an (28) into (32), I b(OFF) is derived as:
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In addition, I b(ON) can be given as:
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Using the volt-second balance principle on Lm , yields:
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Substituting (27), (31), (33), and (34) into (35), the actual voltage gain can be obtained as follows:
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The curves of the ideal and actual voltage gain under n =3, r N1 = r N2 =100 mΩ, r D2 =50 mΩ, r S2 =50 mΩ, V FD2 =1.25 V, Vbat =24 V, and RL =200 Ω are plotted in Fig. 11 . It can be seen that the proposed converter in the discharging mode can achieve a high step-up voltage gain.
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Ideal and actual voltage gain in discharging mode.
When the proposed converter is operating in the BCM, typical waveforms are shown in Fig. 12 . Thus, the peak value of the magnetizing-inductor current is given as:
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Applying the ampere-second balance principle on the capacitor Cbus , the following equation is found:
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From the above equation, the peak value of the magnetizing-inductor current is rewritten as:
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Then, the normalized inductor time constant is defined as:
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Substituting (24), (37), (40) into (39), the boundary inductor time constant is obtained as follows:
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At k = 1, τ Lm2 can be rewritten as:
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If τ Lm2 is larger than τ Lm2,B , the proposed converter in the discharging mode is operated in the CCM.
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Some waveforms of proposed converter with BCM operation at discharging mode.
IV. EXPERIMENTAL RESULTS
In order to verify the feasibility of the proposed converter, a prototype circuit is built for a fuel-cell and battery hybrid power supply system. The electric specifications and circuit components are selected as the input voltage Vin = 28~36.5 V, output power Po = 200~20 W, battery voltage Vbat = 24 V, DC-bus voltage Vbus = 200 V, switching frequency fs = 50 kHz, coupled inductor Lm = 72 μ H and n = 3, capacitors CB = C 1 = Cbus = 220 μ F, switches S 1 (IXFH80N085) and S 2 (IXTQ96N20P), and diodes D 1 (DSSK60-02AR) and D 2 (DSEP30-06A).
Fig. 13 shows the experimental results at the charging mode. The electrical specifications are Vin = 28 V, Vbat = 24 V, and full load Po = 200 W. From Figs. 13 (a) and 13 (c), it can be seen that the current waveforms, i S1 and iLm , are same during the S 1 ON-period. As can be seen from Figs. 13 (b) and 13 (c), the current waveforms, i S2 and iLm , are the same during the S 1 OFF-period. Fig. 13 (c) shows that the proposed converter is operated in the CCM. The measured efficiency at the charging mode is shown in Fig. 15 . The measured efficiency is around 95.2%~97.5% under Vin = 28~36.5 V and Po = 200~20 W. Fig. 14 shows the experimental results at the discharging mode. The electrical specifications are Vbat = 24 V, Vbus = 200 V, and full load Po = 200 W. The waveforms, v gs2 , v S2 , and i S2 , are shown in Fig. 14 (a). It can be seen from the waveform i S2 that the proposed converter is operated in the CCM. From the waveform v S2 , the voltage across S 2 is clamped at approximately 70 V during the S 2 OFF-period. Therefore, a low rated voltage MOSFET can be adopted to reduce the conduction loss. As shown in Fig. 14 (b), the voltage across D 1 is clamped at approximately 70 V during the S 2 OFF-period. The waveforms, i D1 and i Lk1 , are shown in Figs. 14 (b) and 14 (c). It can be seen that they consist with the operating principle. The measured efficiency at the discharging mode is shown in Fig. 15 . The measured efficiency is around 93.3%~95.4%.
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Experimental waveforms of proposed converter at charging mode. (a) vgs1, vS1, iS1, (b) vgs2, vS2, iS2, (c) Vbat, iLm.
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Experimental waveforms of proposed converter at discharging mode. (a) vgs2, vS2, iS2, (b) vD1, iD1, (c) Vbus, iLk1.
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Measured efficiency of proposed converter.
V. CONCLUSIONS
In the conventional hybrid power supplied system, two power converters are used for the battery charging or discharging modes. The conventional system results in energy waste. A new DC-DC converter for renewable energy and battery hybrid power supplied systems is investigated in this paper. At the charging mode, a renewable energy source can provide its energy to charge the battery via the proposed converter. At the discharging mode, the battery can release its energy to the DC bus via the proposed converter. Thus, only one power converter is utilized at the charging or discharging modes. The proposed converter can increase the conversion efficiency. The measured efficiency is around 95.2%~97.5% at the charging mode and it is around 93.3%~95.4% at the discharging mode.
BIO
Lung-Sheng Yang was born in Taiwan, ROC, in 1967. He received his B.S. degree in Electrical Engineering from the National Taiwan Institute of Technology, Taipei, Taiwan, in 1990; his M.S. degree in Electrical Engineering from National Tsing Hua University, Hsinchu, Taiwan, in 1992; and his Ph.D. degree in Electrical Engineering from National Cheng Kung University, Tainan, Taiwan, in 2007. He is presently working as an Assistant Professor in the Department of Electrical Engineering, Far East University, Tainan, Taiwan. His current research interests include power factor correction, dc-dc converters, renewable energy conversion, and electronic ballasts.
Chia-Ching Lin was born in Taiwan, ROC, in 1959. He received his B.S. degree from the Department of Electrical Engineering, Far East University, Tainan, Taiwan, in 1980; and his M.S. degree in Electrical Engineering from National Cheng Kung University, Tainan, Taiwan, in 2006. He is presently working as an Assistant Professor in the Department of Electrical Engineering, Far East University. His current research interests include power factor correction and dc-dc converters.
References
Bialasiewicz J. T. 2008 “Renewable energy systems with photovoltaic power generators: operation and modeling,” IEEE Trans. Ind. Electron. 55 (7) 2752 - 2758    DOI : 10.1109/TIE.2008.920583
Carrasco J. M. , Franquelo L. G. , Bialasiewicz J. T. , Galvan E. , Guisado R. C. P. , Prats M. A. M. , Leon J. I. , Alfonso N. M. 2006 ”Power-electronic systems for the grid integration of renewable energy sources: a survey,” IEEE Trans. Ind. Electron. 53 (4) 1002 - 1016    DOI : 10.1109/TIE.2006.878356
Kwon S. K. , Sayed K. F. A. 2008 “Boost-Half bridge single power stage PWM DC-DC converter for PEM-fuel cell stacks,” Journal of Power Electronics 8 (3) 239 - 247
Nejabatkhah F. , Danyali S. , Hosseini S. H. , Sabahi M. , Niapour S. M. 2012 “Modeling and control of a new three-input DC-DC boost converter for hybrid PV/FC/battery power system,” IEEE Trans. on Power Electron. 27 (5) 2309 - 2324    DOI : 10.1109/TPEL.2011.2172465
Ahmedy T. , Nishida K. , Nakaoka M. 2010 “Wind power grid integration of an IPMSG using a diode rectifier and a simple MPPT control for grid-side inverters,” Journal of Power Electronics 10 (5) 548 - 554    DOI : 10.6113/JPE.2010.10.5.548
Juan Y. L. 2011 “An integrated-controlled AC/DC interface for microscale wind power generation systems,” IEEE Trans. Power Electron. 26 (5) 1377 - 1384    DOI : 10.1109/TPEL.2010.2081378
Xia C. , Geng Q. , Gu X. , Shi T. , Song Z. 2012 “Input-output feedback linearization and speed control of a surface permanent-magnet synchronous wind generator with the boost-chopper converter,” IEEE Trans. Ind. Electron. 59 (9) 3489 - 3500    DOI : 10.1109/TIE.2011.2171172
Chen Y. M. , Huang A. Q. , Yu X. 2013 “A high step-up three-port DC-DC converter for stand-alone PV/battery power systems,” IEEE Trans. Power Electron. 28 (11) 5049 - 5062    DOI : 10.1109/TPEL.2013.2242491
Lee J. H. , Liang T. J. , Chen J. F. 2014 “Isolated coupled inductor integrated DC-DC converter with non-dissipative snubber for solar energy applications,” IEEE Trans. Ind. Electron. 61 (7) 3337 - 3348    DOI : 10.1109/TIE.2013.2278517
Ryu H. M. 2011 “Highly efficient AC-DC converter for small wind power generators,” Journal of Power Electronics 11 (2) 188 - 193    DOI : 10.6113/JPE.2011.11.2.188
Liao Z. , Ruan X. “A novel power management control strategy for stand-alone photovoltaic power system,” IEEE International Power Electronics and Motion Control Conference 2009 445 - 449
Jang S. J. , Lee T. W. , Lee W. C. , Won C. Y. “Bi-directional DC-DC converter for fuel cell generation system,” IEEE Power Electronics Specialists Conference 2004 4722 - 4728
Jin K. , Ruan X. , Yang M. , Xu M. 2009 “A hybrid fuel cell power system,” IEEE Trans. Ind. Electron. 56 (4) 1212 - 1222    DOI : 10.1109/TIE.2008.2008336
Choi D. K. , Lee B. K. , Choi S. W. , Won C. Y. , Yoo D. W. 2005 “A novel power conversion circuit for cost-effective battery-fuel cell hybrid systems,” Journal of Power Sources 152 245 - 255    DOI : 10.1016/j.jpowsour.2005.01.050
Liu W. S. , Chen J. F. , Liang T. J. , Lin R. L. 2011 “Multicascoded sources for a high-efficiency fuel-cell hybrid power system in high-voltage application,” IEEE Trans. Power Electron. 26 (3) 931 - 942    DOI : 10.1109/TPEL.2010.2089642
Li W. , Wu H. , Yu H. , He X. 2011 “Isolated winding-coupled bidirectional ZVS converter with PWM plus phase-shift (PPS) control strategy,” IEEE Trans. Power Electron. 26 (12) 3560 - 3570    DOI : 10.1109/TPEL.2011.2162852
Samosir A. S. , Yatim A. H. M. 2010 “Implementation of dynamic evolution control of bidirectional DC-DC converter for interfacing ultracapacitor energy storage to fuel-cell system,” IEEE Trans. Ind. Electron. 57 (10) 3468 - 3473    DOI : 10.1109/TIE.2009.2039458
Sreekumar C. , Agarwal V. 2007 “Hybrid control approach for the output voltage regulation in buck type DC-DC converter,” IET Electr. Power Appl. 1 (6) 897 - 906    DOI : 10.1049/iet-epa:20070043
Santos E. C. D. 2013 “Dual-output DC-DC buck converters with bidirectional and unidirectional characteristics,” IET Power Electron. 6 (5) 999 - 1009    DOI : 10.1049/iet-pel.2012.0731
Zhao Q. , Lee F. C. 2003 “High-efficiency, high step-up DC-DC converters,” IEEE Trans. Power Electron. 18 (1) 65 - 73    DOI : 10.1109/TPEL.2002.807188