Tapped-Inductor Filter Assisted Soft-Switching PWM DC-DC Power Converter

Transcription

1 I. INTRODUCTION Tapped-Inductor Filter Assisted Soft-Switching PWM DC-DC Power Converter SERGUEI MOISSEEV KOJI SOSHIN MUTSUO NAKAOKA, Member, IEEE Yamaguchi University Japan A novel high-frequency transformer linked full-bridge type soft-switching phase-shift pulsewidth modulated (PWM) controlled dc-dc power converter is presented, which can be used as a power conditioner for small-scale photovoltaic and fuel cell power generation systems as well as isolated boost dc-dc power converter for automotive ac power supply. In these applications with low-voltage large-current sources, the full-bridge circuit is the most attractive topology due to the possibility of using low-voltage high-performance metal-oxide-semiconductor field-effect transistor (MOSFET) and achieving high efficiency of the dc-dc power converter. A tapped-inductor filter including the freewheeling diode is newly implemented in the output stage of the full-bridge phase-shift PWM dc-dc converter to achieve soft-switching operation for the wide load variation range. Moreover, in the proposed converter circuit, the circulating current is effectively minimized without using additional resonant circuit and auxiliary power switching devices. The practical effectiveness of the proposed soft-switching dc-dc power converter was verified in laboratory level experiment with 1 kw 100 khz breadboard setup using power MOSFETs. Actual efficiency of 94 97% was obtained for the wide duty cycle and load variation ranges. A variety of the high-frequency transformer linked dc-dc converter circuit topologies have been for fuel cell power generation systems and 42 V automotive ac power supplies. In these systems with relatively low input voltage and large input current, due the capability of reducing power devices voltage and current peak stresses, lower switching power losses, and electromagnetic noises, the high-frequency step-up transformer zero voltage switchings (ZVS) phase-shifted pulsewidth modulated (PS-PWM) full-bridge isolated dc-dc power converters have attracted much attention [1]. However, there is a large circulating current in the ZVS PS-PWM full-bridge dc-dc converter. This current flows through the high-frequency transformer and its primary side circuit during the freewheeling interval as a consequence of the PS-PWM control strategy [2 4]. Due to this current, the conduction power losses in the ZVS PS-PWM dc-dc converter are higher compared with those of the hard-switching PWM dc-dc converter. This problem becomes especially significant in the dc-dc power converters with the low-voltage and large-current sources, like the above mentioned photovoltaic and fuel cells and automobile batteries. Moreover, in the conventional ZVS full-bridge dc-dc power converter, the soft-switching operation is not obtainable for lagging bridge-leg power metal-oxide-semiconductor field-effect transistor (MOSFET) due to insufficient current to charge/discharge lossless snubber capacitors of these power MOSFETs under the light load [4 8]. A new full-bridge PS-PWM dc-dc power converter with ZVS and zero current switching (ZCS) bridge legs, using the tapped-inductor filter in the output stage is presented. In the proposed dc-dc converter, the soft-switching operation range is enlarged to 10% 100% output load. The circulating current is effectively reduced without using additional resonant circuit and auxiliary power switching devices. The 36 V input voltage 1 kw-100 khz prototype circuit using power MOSFETs is built and tested in the experiment. Actual efficiency of the proposed dc-dc converter is achieved 94 97% over the wide duty cycle and load variation ranges. Manuscript received September 10, 2001; revised June 11, 2004; released for publication September 16, IEEE Log No. T-AES/41/1/ II. PROPOSED SOFT-SWITCHING DC-DC CONVERTER CIRCUIT Refereeing of this contribution was handled by M. G. Simoes. Authors address: 2-1-1, Tokiwadai Dept. of Electrical and Electronics Engineering, Yamaguchi University, Ube City, Yamaguchi, Japan, Postal Code , (sergey@pe news1.eee.yamaguchi u.ac.jp) /05/$17.00 c 2005 IEEE A. Circuit Configuration Fig. 1 shows a schematic circuit topology of the proposed high-frequency transformer linked full-bridge soft-switching PS-PWM dc-dc power converter with tapped-inductor filter L d1 =L d2 in its output stage. In fact, the full-bridge dc-dc converter 174 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 41, NO. 1 JANUARY 2005

2 Fig. 1. Proposed full-bridge type soft-switching PS-PWM dc-dc power converter with trapped inductor filter. is a buck converter, however, the boost characteristic of the full-bridge dc-dc converter can be achieved by selecting step-up high-frequency transformer Tr with suitable turns ratio a T,wherea T = n p =n s and n p and n s are the primary and secondary windings numbers, respectively (see Fig. 1). The lossless-snubber capacitors C 1 and C 2 in parallel with leading bridge-leg active semiconductor devices (power MOSFETs) Q 1 (switch S 1 /diode D 1 )andq 2 (S 2 =D 2 ) make the power MOSFETs Q 1,Q 2 operate with ZVS transitions. The lagging bridge-leg power MOSFETs Q 3 and Q 4 operate with ZCS at turn-on with the aid of the inductance L s.this inductance L s can be presented by leakage inductance of the high-frequency transformer Tr. On the other hand, the tapped-inductor filter L d1 =L d2 including a freewheeling diode is used to obtain ZCS for the power MOSFETs Q 3 and Q 4 at turn-off as well as to minimize circulating current during the freewheeling interval. B. Circuit Operation Fig. 2 illustrates switching-pulse sequences and theoretical voltage and current waveforms of the presented dc-dc converter in a steady state. The switches S 1 and S 2 are driven complementary with the short blanking interval t d to protect circuit from shorting and to achieve ZVS commutation at the turn-on instant. The output voltage E 0 is regulated by shifting the gate-pulse of the lagging bridge-leg switches from gate-pulse of the leading bridge-leg switches and thus varying the interval t on (t on = DT=2) as phase-shifted PWM control strategy with the constant switching frequency f =1=T. The operating principle of the proposed dc-dc converter circuit under the steady-state condition can be described as follows. The main operation mode during a half period of the steady state operation is showninfig.3. Fig. 2. Calculated waveforms of proposed soft-switching PS-PWM dc-dc power converter. Mode 1(t<t 0 ): Before time t 0, it is assumed that the switches S 1,S 4 and the rectifier diodes D 5,D 8 are conducting. Mode 2(t 0,t 1 ): At the instant t 0,theswitch S 1 (Q 1 ) is turned off under principle of ZVS with the aid of the lossless-snubber capacitors C 1 and C 2 (C 1 =C 2 = C). The voltage v Q1 across the switch S 1 (Q 1 ) rises as follows, dv Q1 (t) = i m (t 0 )+i D5 (t 0 )= T : (1) dt 2C After that, the rectified voltage v d decreases in accordance with the following equation, v d (t)= (E v Q1 (t)) : (2) T The freewheeling diode D 9 starts to conduct when v d reaches the certain value L E 0,where L is the turns ratio of the tapped-inductor defined as L = n 2 =(n 1 + n 2 ); n 1, n 2 are the number of turns of MOISSEEV ET AL.: TAPPED-INDUCTOR FILTER ASSISTED SOFT-SWITCHING PWM DC-DC POWER CONVERTER 175

3 Fig. 3. Equivalent circuits during half period of steady state operation. L d1 and L d2, respectively. The rectifier current i d5 decreases and it is expressed by the following equation, di D5 (t) dt = 2 T L E 0 L S : (3) Mode 3(t 1,t 3 ): Due to the presence of the leakage and magnetizing inductances in the transformer Tr its primary side diode D 2 becomes forward biased and, therefore, starts to conduct. After the rectified current i d5 reaches zero at the instant t 1, the freewheeling current i 1 becomes equal to the magnetizing current of the high frequency transformer Tr. The whole output current flows through D 9, L d2 and L d1. At the instant t 2, pulse signal v g2 is applied to the switch S 2 or Q 2.TheswitchS 2 is turned on with ZVS. The circulating current i 1 flows through the transformer Tr and its primary side circuit consisted of the diode D 2 and the switch S 4. This interval ends when the switch S 4 is turned off with ZCS at the instant t 3. Mode 4(t 4,t 5 ): At the instant t 4,theswitchS 3 is turned on with ZCS due to the effect of the leakage inductance L S. The current through the switch S 3 rises as shown by the following equation, di Q3 dt ¼ E E 0 T L L S : (4) The output current reflected to the primary side of the transformer flows through the switches S 2 (Q 2 ) and S 3. On the other hand, the current i D9 through L d2 and D 9 decreases and the diode D 9 turns off. During Mode 4, the energy is being delivered through the switches S 2,S 3, and high-frequency transformer Tr, and rectifier diodes D 6,D 7. The half cycle of operation ends at the instant t 5. The operation during the next half-cycle is symmetrical with the mentioned one half-cycle. In the proposed dc-dc converter, the switches S 1 (Q 1 )ands 2 (Q 2 ) are turned on and turned off with ZVS, while the switches S 3 and S 4 operate with ZCS at turn-on and turn-off. The circulating current during freewheeling interval t 0 t 3 (see Fig. 2) is substantially lowered without using any additional auxiliary resonant snubber circuits or active semiconductor devices. III. OUTPUT VOLTAGE CHARACTERISTICS AND TAPPED-INDUCTOR TURNS RATIO DESIGN The tapped-inductor filter L d1 =L d2 including freewheeling diode D 9 acts as a passive voltage clamp element in the proposed soft-switching PS-PWM dc-dc converter, so that the rectified output voltage v d is clamped to the positive polarity during the freewheeling interval (t 0 t 3 ). Therefore, the rectifier diode D 5 (D 6 ) becomes reverse biased, and the output current flows through the secondary side freewheeling diode D 9 during the freewheeling interval. As a result, the circulating current i 1 through the transformer and its primary side circuit is effectively reduced. Fig. 4 shows the rectified voltage v d and rectified current i D5 theoretical waveform. 176 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 41, NO. 1 JANUARY 2005

4 Fig. 4. Operating waveforms of rectified voltage v d and rectified current i D5. During a half-cycle period, the rectified voltage v d is expressed by, v d = N L E 0 for t 0 <t t 4 v d = E N T for t 4 <t t 5 : (5) The output voltage characteristic of the proposed dc-dc power converter can be represented by the following expression, E 0 = DE T f1 L (1 D)g L s I 0 2 T T h f1 L (1 D)g2 : (6) To make the average output voltage E 0 characteristic independent of the output current I 0, and to obtain effective cancellation of the circulating current, the leakage inductance L s of the high-frequency transformer Tr is designed as small as possible. The design of the tapped-inductor L d1 =L d2 turns ratio is made on the basis of the simulation results under the closed loop control scheme. The simulated waveforms of the transformer primary side current i 1, inductor L d1 current i Ld1, and rectified voltage v d are shown in Fig. 5. To achieve effective circulating current minimization and, at the same time, to prevent the increase of the output current ripples, the tapped-inductor turns ratio is set to 0.3 for dc-dc converter designed for 100 khz operating frequency. IV. EXPERIMENTAL RESULTS To verify the operating principle and steady state performances, the experiment was carried out with a 1 kw 100 khz prototype circuit. To achieve high efficiency and high performances of the dc-dc converter, power MOSFETs were selected as the active semiconductor devices. The power circuit components parameters are indicated in Table I. The three series-connected 12 V automobile batteries Fig. 5. Calculated results under closed loop control. (a) Waveforms of transformer primary side current i 1. (b) Waveforms of filter inductor L d1 current i ld1. (c) Waveforms of the recified voltage v d. Fig. 6. External appearance of tapped inductor. were used as 36 V dc power supply for the tested dc-dc converter. To reduce conduction power losses in the high-frequency inverter stage of the proposed converter, 2 power MOSFETs were connected in parallel. Fig. 6 demonstrates the external appearance of the tapped inductor L d1,l d2,whichwasusedinthe experiment. Fig. 7 illustrates the experimental results of the tested dc-dc converter under a condition of 50% full load. The measured voltage and current waveforms of the high-frequency transformer Tr and power MOSFET Q 4, gate-pulse voltage of the power MOSFET Q 2, and voltage across this device are presented in Fig. 7(a), (b), and (c), respectively. Observing waveforms of Fig. 7(a), it can be concluded that the circulating current is substantially MOISSEEV ET AL.: TAPPED-INDUCTOR FILTER ASSISTED SOFT-SWITCHING PWM DC-DC POWER CONVERTER 177

5 TABLE I Design Specifications and Circuit Parameters Item Symbol Value Input Voltage E in 36 V Operating frequency f 100 khz 2SK3228, V DS =80 V, MOSFETs Q 1 Q 4 R DS =0:006, I DS =75 A (2 switches in parallel) Diodes D 5 D 8 FML33S V RRM = 300 V, I O =20 A Lossless snubber capacitors C 1,C 2 25 nf Transformer turns ratio T 1:4 Magnetizing inductance L m 70 ¹H Leakage inductance L S 300 nh Tapped inductor L d1,l d2 L d1 =50 ¹H, L d2 =13 ¹H Core: Ferrite PQ 50/50 Tapped inductor turns ratio L 0.3 Output capacitor C d 250 ¹F Fig. 8. Output Eo and input voltage E characteristic as function of output current Io. Fig. 7. Experimental results. E =36 V, Eo = 110 V, Io =5 A, D =0:65. (a) High frequency transformer voltage v ab and current i 1 waveforms. Scale: v: [20 V/div], i: [20 A/div], time: [2 ¹s/div]. (b) MOSFETs Q 4 voltage v Q4 and current i Q4 waveforms. Scale: v: [20 V/div], i: [10 A/div], time: [2 ¹s/div]. (c) Gate signal voltage v g2 and voltage v Q2 across MOSFETs Q 2 waveforms. Scale: v g2 : [10 V/div], v Q2 : [20 V/div], time: [2 ¹s/div]. lowered without using any additional resonant or active auxiliary snubber circuits. Moreover, as shown in Fig. 7(b) and (c), the power MOSFET Q 4 operates with ZCS at turn-on and turn-off, while the power MOSFETs Q 2 turns off and turns on with ZVS. The soft-switching conditions for the lagging bridge leg power MOSFETs Q 3 and Q 4 were obtained from no load to full load. The ZVS operation ranges for the power MOSFETs Q 1 and Q 2 of the leading bridge legs were realized from 10% to 100% load. Fig. 9. Actual efficiency and total power losses as function of load current I 0. The output voltage characteristics Eo of the proposed dc-dc power converter as a function of the output current Io under the different duty cycle values D =0:5 0.7 are shown in Fig. 8. Fig. 9 demonstrates the measured actual efficiency and the total power losses as functions of the output 178 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 41, NO. 1 JANUARY 2005

6 current Io under the duty cycle values D =0: The actual efficiency 94 97% was achieved over the wide duty cycle and load variation ranges. V. CONCLUSIONS The new high-frequency transformer linked full-bridge type soft-switching PS-PWM controlled dc-dc power converter with ZVS and ZCS bridge-legs was presented in this paper for the low-voltage and large-current input side power supplies. The generation of the conduction losses due to circulating current during freewheeling period was suppressed by using tapped inductor filter including freewheeling diode. The high-efficiency stable soft-switching operation ability of the proposed dc-dc power converter was verified on the basis of the experimental results using 1 kw 100 khz breadboard circuit using low-voltage high-performance power MOSFETs. The proposed soft-switching dc-dc power converter has enough ability to be used as high performance isolated type dc-dc power conditioner for 1 kw class photovoltaic or fuel cell power generation systems and for step-up isolated dc-dc converter of automotive ac power supply. REFERENCES [1] Patterson, O. D., and Divan, D. M. Pseudo-resonant full bridge DC/DC converter. IEEE Power Electronics Specialists Conference Record, June 1987, [2] Kim, E. S., Joe, K. Y., Key, M. H., Kim, Y. H., and Yoon, B. D. An improved soft-switching PWM FB DC/DC converter for reducing conduction losses. IEEE Transactions on Power Electronics, 14, 2 (1999), [3] Cho, J. G., Back, J. W., Jeong, C. Y., Yoo, D. W., and Joe, K. Y. Novel zero-voltage and zero-current-switching full bridge PWM converter using transformer auxiliary winding. IEEE Transactions on Power Electronics, 15, 2 (2000), [4] Jeon, S. J., and Cho, G. H. A zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation. IEEE Transactions on Power Electronics, 16, 5 (2001), [5] Seok, K. W., and Kwon, B. H. An improved zero-voltage and zero-current-switching full-bridge PWM converter using a simple resonant circuit. IEEE Transactions on Industrial Electronics, 48, 6 (2001), [6] Moisseev, S., Hamada, S., Ishitobi, M., Hiraki, E., and Nakaoka, M. High-frequency forward transformer linked PWM DC-DC power converter with zero voltage switching and zero current switching bridge legs. KIPE Journal of Power Electronics, 2, 4 (2002), [7] Moisseev, S., Sato, S., Hamada, S., and Nakaoka, M. Full bridge soft-switching phase-shifted PWM DC-DC converter using tapped inductor filter. In Proceedings of IEEE Power Electronics Specialists Conference, Vol. 4, June 2003, [8] Moisseev, S., Hamada, S., and Nakaoka, M. Full-bridge soft-switching phase-shifted PWM DC-DC power converter using tapped inductor filter. IEE-UK Electronics Letters, 39, 12 (June 2003), MOISSEEV ET AL.: TAPPED-INDUCTOR FILTER ASSISTED SOFT-SWITCHING PWM DC-DC POWER CONVERTER 179

7 Serguei Moisseev was born in Arsenyev (Primorye), Russia in He received the B.Eng. in electro-mechanical engineering from Far-East State Maritime Academy, Vladivostok, Russia in He received the M.Eng. degree from the Department of Electrical and Electronics Engineering, Yamaguchi University, Japan in He is currently a Ph.D. candidate student of Division of Systems Engineering, the Graduate School of Science and Engineering, Yamaguchi University, Japan. His research interests include soft-switching high-frequency PWM dc-dc converters for high power applications. Mr. Moisseev is a student member of the IEE Japan. Koji Soshin received his M.Sc.Eng. from the Electronic Engineering Department, the Graduate School of Electrical and Electronics Engineering,. Kobe University, Kobe, Japan. He is now a Ph.D. candidate student in the Graduate School of Science and Engineering, Yamaguchi University, Yamaguchi, Japan. He joined Matsushita Electric Works, Ltd. in He is interested in stepping motor applications, vector controlled inverter for the induction motor and power electronic circuits and systems technologies. He is now working in the power supplies for electric vehicles. Mr. Soshin is a member of the Japan Society of Power Electronics. Mutsuo Nakaoka (M 83) received his Ph.D. degree in electrical engineering from Osaka University, Osaka, Japan in He joined in the Electrical and Electronics Engineering Department, Kobe University, Kobe, Japan in Since 1995, he has been a professor in the Electrical and Electronics Engineering Department, the Graduate School of Science and Engineering, Yamaguchi University, Yamaguchi, Japan. His research interests include circuit and control systems of power electronics, especially in soft-switching areas. Dr. Nakaoka is a member of the Institute of Electrical Engineers of Japan, the Institute of Electronics, Information and Communication Engineers of Japan, the Institute of Illumination Engineering of Japan. 180 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 41, NO. 1 JANUARY 2005