A novel zero-voltage zero-current switching full-bridge PWM DC-DC converter with controlled secondary side
rectifier is presented in this paper. Zero-voltage turn-on and zero-current turn-off for all power switches of the inverter is
achieved for full load range from no-load to short circuit by using turn-off snubber and secondary energy recovery clamp.
Modified PWM control strategy is used for the converter. The principle of operation is explained and analysed and simulation
results are presented

Dudrik, Jaroslav

Ruščin, V.

Advances in Electrical and Electronic Engineering

This paper presents research motivated by industrial demand for special traction drive topology devoted tominimization of traction transformer weight against topology with classical 50Hz traction transformer. The special tractiondrive topology for AC power systems consists of input high voltage trolley converter (single phase matrix converter) –middle frequency transformer – output converter - traction motor has been described. The main attention has been given tothe control algorithm of the traction topology (inserting of NULL vector of matrix converter and Two-value control ofsecondary active rectifier)

Jaroslav Durdik

Vladimir Ruscin

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ZVZCS PWM DC-DC Converter with energy recovery clamp 99 ZVZCS PWM DC-DC CONVERTER WITH ENERGY RECOVERY CLAMP   J. Dudrik, V. Rušin  Department of Electrical, Mechatronic and Industrial Engineering, Technical University of Košice, Letná 9, 04200 Košice, Slovak Republic E-mail: jaroslav.dudrik@tuke.sk, phone: +421 55 6022276, fax: +421 55 6330115  Summary A novel zero-voltage zero-current switching full-bridge PWM DC-DC converter with controlled secondary side rectifier is presented in this paper. Zero-voltage turn-on and zero-current turn-off for all power switches of the inverter is achieved for full load range from no-load to short circuit by using turn-off snubber and secondary energy recovery clamp. Modified PWM control strategy is used for the converter. The principle of operation is explained and analysed and simulation results are presented.   1. INTRODUCTION  The conventional phase shifted PWM converters are often used in many applications because their topology permits all switching devices to operate under zero-voltage switching by using circuit parasitics such as power transformer leakage inductance and devices junction capacitance.  However, because of phase-shifted PWM control, the converter has a disadvantage that circulating current flows through the power transformer and switching devices during freewheeling intervals. To decrease the circulating current to zero and thus to achieve zero-current switching, various snubbers, auxiliary circuits and/or clamps connected mostly at the secondary side of power transformer are applied [1] – [10]. The disconnection of the secondary windings is usually achieved by application of the reverse bias for the output rectifier or using controlled rectifier.  The optimal switching for IGBTs is zero-voltage turn-on and mainly zero-current turn-off due to elimination of the current tail influence, which has considerable high involvement in creation of the IGBT turn-off losses.  2. POWER CIRCUITS OF THE PROPOSED CONVERTER  To achieve the aims mentioned above, the topology of the following ZVZCS converter was designed.  The DC-DC converter shown in Fig.1 consists of high-frequency inverter, power transformer, output rectifier, output secondary switch and output filter. The main part of the converter includes high frequency full-bridge inverter consisting of the four ultrafast IGBT´s T1-T4 and freewheeling diodes D1-D4. The secondary winding of the high-frequency step-down power transformer TR is connected through a fast recovery rectifier D5, D6 and secondary switch T5 to output filter consisting of smoothing choke L0 and capacitor C0. The converter is controlled by modified pulse-width modulation (Fig.2), and consequently the zero-voltage turn-on and zero-current turn-off all of the transistors T1-T4 in the inverter are reached.    I n p u t  S o u r c e  T 1  D 3  u P  T 3  D 2  T 2  L S  D 5  i P  T 4  D 1  D 4  U  _  L O  C O  T 5  D C 1  T R  D O  R O  C C 1  D 6  C S 1  D S 1  C S 2  D S 2  D S 3   A u x i l i a r y  D C / D C  C o n v e r t e r  U O  U C C 1  U d  U S  U S  I 0  A  E n e r g y  r e c o v e r y  c l a m p  T u r n - o f f  s n u b b e r  A    Fig.1. Scheme of the proposed ZVZCS PWM DC-DC converter  100 Advances in Electrical and Electronic Engineering The semiconductor switch T5 in the secondary side is used to reset secondary and consequently also primary current. The transistor T5 operates with double switching frequency. At turn-off of the switch T5 the energy stored in leakage inductance is clamped by DC1 and CC1 and then transferred trough auxiliary dc-dc converter to the input source. By using non-dissipative snubber to reduce turn-off losses of the transistor T5, the overall efficiency is increased.   3. OPERATION PRINCIPLE  The basic operation of the proposed soft switching converter has eight operating modes (intervals) within each half cycle. The switching diagram and operation waveforms are shown in Fig. 2.    iP  iD O  u P  u S iC S 1  iD  T 1 ,  T 2 T 3 , T 4 T 5  T 5  t0 t 1 t2  t3         t 4 t5     t6                   t 7  t8  U  iD C 1  T 1,  T 2  T 5 iD 5 iD 6 iD O  iD 0 iD 5 iT 5 td IP  Iµ  U S U C C 1  U S  IT 5m  IC S = IT5 m /2  I Dm a x I LS m ax  I Dm in ID m a xID m in+I LS m ax  0  0  0  0  0  0  0  0  0  t t t t t t t t   Fig. 2 Operation waveforms of the converter  4. SIMULATION RESULTS  A simulation model in programme Orcad was created to verify the properties of the proposed converter. The simulations were made at input voltage U = 320V. Parameters: Transformer TR parameters: Turns ratio n = 6,  Magnetizing inductance Lm = 800 H, Leakage inductance LLP = 7 H. Snubber circuit parameters: Snubber capacitors CS1 = CS2= 56 nF, Snubber inductance LS = 5 H. Set value of clamp voltage UCC1 = 80 V  The following waveforms were obtained at resistive load. Fig.3 shows switch voltage uCE4 and switch current iC4+iD4 during turn-on and turn-off of the transistor T4 in the converter. The switch (transistor T4 including diode D4) is turned-on under zero-voltage because at turn-on of the transistor T4 its freewheeling diode D4 is in on state. Moreover the rate of rise of the collector current is limited by the leakage inductance LLP of the transformer.  The transistor turn-off losses are negligible because transistor T4 turns-off only small magnetizing current (about 1.5 Amp in this case) as can be seen in the Fig.3.              Tim e168. 0us 17 0.0 us 1 72. 0us 17 4.0u s 176 .0us 1 78.0 us 18 0.0u s1  IC(Z 4)- I(D4 ) 2   V(P 1)0A4A8A12A-3A1    > >-1 00V0V1 00V2 00V3 00V4 00V2  Fig. 3. Switch (transistor T4 + diode D4) voltage uCE4 and switch current iC4+iD4.  Collector-emitter voltage uDS and collector current iD of the secondary transistor T5 (bottom waveforms) is shown in Fig. 4. The secondary switch (transistor T5) is turned-on under zero-current due to influence of the leakage inductance of the transformer LLS reflected to the secondary side and snubber inductance LS.  The turn-off loss is reduced by snubber capacitors CS1 and CS1 acting as the non-dissipative snubber as it is evident in Fig. 4.              Time169u s 170us 1 71us 17 2us 17 3us 174 us 175u s 176us 1 77us 1 78usI(Rco llect or) V(M1: d)- V (M1:s )-20020406080100 Fig. 4. Collector-emitter voltage uDS and collector current iD of the secondary transistor T5         Rectified voltage ud and output diode current iD5 is shown in Fig. 5.  ZVZCS PWM DC-DC Converter with energy recovery clamp 101            Time178 us 180 us 182u s 18 4us 18 6us 18 8us 190 us 19 1usI( D5)0 A50 A100 ASEL >>V( UD)0 V50 V100 V Fig. 5. Rectified voltage ud (upper waveform) Output diode current iD5 (bottom waveform)  During commutation between secondary diode and output freewheeling diode the secondary voltage and accordingly rectified secondary voltage is zero.  At turn-off of the secondary switch T5 the secondary and also rectified voltage rises as a result of energy stored in leakage inductance. The over-voltage US can be maintained on acceptable value by proper design of the auxiliary dc-dc converter. Fig. 6 shows the snubber capacitor current at turn-on and turn-off of the secondary switch T5 (bottom waveform).              Time169us 170us 171us 172us 173us 174us 175us 176us 177us 178usI(Cs1)0A25A50A-20ASEL>>I(Rcollector) V(M1:d)- V(M1:s)050100 Fig. 6. Collector voltage uDS and collector current iD of the secondary transistor T5 (upper waveforms) Snubber capacitor current iCS1 (bottom waveform)   5. CONCLUSION  Soft switching and reduction of circulating currents in the proposed converter are achieved for full load range using the secondary side turn-off and energy recovery clamp in combination with modified PWM control. At proper design it is possible to utilize the magnetizing current of power transformer for charging or discharging output capacitances of the IGBT switches and thus zero-voltage turn-on of the IGBTs to achieve.  The IGBT transistors are turned-off almost under zero current. Only negligible magnetizing current of the power transformer is turned-off by IGBT transistors. The main task of the proposed secondary energy recovery clamp is the transfer the leakage inductance energy to the input source at turn-off of the secondary switch. Turn-off snubber is employed to improve turn-off process of the secondary switch. Using leakage inductance of the power transformer working as a turn-on snubber it is ensured zero current turn-on process of the secondary switch. Finally, it is possible to say, that IGBTs in the full bridge inverter operate at almost ideal switching conditions – ZV turn-on and ZC turn-off. Soft switching of the secondary switch and leakage inductance energy transfer to the input source is ensured by turn-off snubber and energy recovery clamp containing only non-dissipative components.   Acknowledgment  This work was supported by Research and Development Support Agency under project APVV-99-031205.   REFERENCES  [1] KIM E. S.,JOE K. Y., KYE M. H., KIM Y. H.,  YOON B. D.: An Improved Soft Switching PWM FB DC-DC Converter for Reducing Conduction Losses, in Record, IEEE PESC’96, Vol. I., pp. 651-656. [2] CHO J. G., RIM G. H., LEE F. C.: Zero Voltage and Zero Current Switching Full Bridge PWM Converter Using Secondary Active Clamp, in Record, IEEE PESC’ 96, Vol. I., pp. 657-663. [3] RINNE K. H., THEML K., MCCARTHY O.: An Improved Zero-Voltage and Zero-Current Switching Full Bridge Converter,” in Record, EPE’ 95, Vol. 2., pp. 725-730. [4] HORVÁTH M., BORKA J.: Welding Technology and Up-to-date Energy Converters. EDPE 2005 Conference, Dubrovnik, Croatia, September 24-26, 2005. CD-Proc. E05-06. [5] LEUCHTER J., BAUER P.: Analysis of Losses in the Power Indirect Converters. Circuits Theory Symposium, ISBN 80-7231-011-9, Brno, 2005, pp. 117-120, (in Czech). [6] TERE, A., FEO, I., PÁNIK, P: DC/DC Converters with Soft (ZVS) Switching. In Conf. Proc. ELEKTRO 2001, section - Electrical Engineering. Žilina 2001, Slovakia, pp. 82 – 90. [7] CHLEBIŠ, P.: Soft Switching Converters. Monograph, VŠB-TU Ostrava, Ostrava, 2004, ISBN 80-248-0643-6, 148 p. (in Czech) [8] HAMAR J., NAGY I.: Bi-directional Resonant Buck & Boost Converter. ELECTROMOTION, Romania, Oct.-Dec. 2001, Vol.8, No. 4, pp.189-195. [9] TRIP N. D.: A New Active Snubber for DC-DC Boost Converters. 8th International Conference on Engineering of Modern Electric System 102 Advances in Electrical and Electronic Engineering Proceedings, Section Electronics, Oradea, Romania, May 2005, pp.124-127. [10] DUDRIK, J., ŠPÁNIK, P., TRIP, N.-D.: Zero Voltage and Zero Current Switching Full-Bridge DC-DC Converter with Auxiliary Transformer. IEEE Trans. on Power Electronics, Vol.21, No.5, 2006, pp. 1328 – 1335. [11] MILLY, D., MAXIM, V.: Simulation and Analysis of Power Converter Input Currents. International Computer Science Conference, MicroCAD'98, February 25-26, Miskolc, Hungary, 1998, pp. 63 – 68. [12] CHO J. G., BAEK J. W., YOO D. W., LEE H. S., RIM G. H.: Novel Zero-Voltage and Zero-Current Switching (ZVZCS) Full Bridge PWM Converter Using Transformer Auxiliary Winding, in Record, IEEE PESC’97, Vol. I., pp. 227-232. [13] CHO J. G., BAEK J. W., JEONG CH. Y., RIM G. H.: Novel Zero-Voltage and Zero-Current Switching Full Bridge PWM Converter Using a Simple Auxiliary Circuit, IEEE Trans. on Industry Applications, Vol. 35, pp. 15-20, 1999. [14] LIU R.: Comparative Study of Snubber Circuits for DC-DC Converters Utilized in High Power Off-line Power Supply Applications, in Record, IEEE APEC 9́9, pp.821-826. [15] DUDRIK J. AND DZURKO P.: An Improved Soft-Switching Phase-Shifted PWM Full-Bridge DC-DC Converter in Record, EPE-PEMC 2́000 Proc., Vol. 2, 2000, Košice, pp. 65-69. [16] PETROV, S.: Expectations of Resonant Converters Utilization as Welding Power Sources. Schematics No. 7, July 2006, pp.30-33 (in Russian).  

ZVZCS PWM DC-DC Converter with Energy Recovery Clamp

DSpace at VSB Technical University of Ostrava

ZVZCS PWM DC-DC Converter with energy recovery clamp 99 ZVZCS PWM DC-DC CONVERTER WITH ENERGY RECOVERY CLAMP   J. Dudrik, V. Rušin  Department of Electrical, Mechatronic and Industrial Engineering, Technical University of Košice, Letná 9, 04200 Košice, Slovak Republic E-mail: jaroslav.dudrik@tuke.sk, phone: +421 55 6022276, fax: +421 55 6330115  Summary A novel zero-voltage zero-current switching full-bridge PWM DC-DC converter with controlled secondary side rectifier is presented in this paper. Zero-voltage turn-on and zero-current turn-off for all power switches of the inverter is achieved for full load range from no-load to short circuit by using turn-off snubber and secondary energy recovery clamp. Modified PWM control strategy is used for the converter. The principle of operation is explained and analysed and simulation results are presented.   1. INTRODUCTION  The conventional phase shifted PWM converters are often used in many applications because their topology permits all switching devices to operate under zero-voltage switching by using circuit parasitics such as power transformer leakage inductance and devices junction capacitance.  However, because of phase-shifted PWM control, the converter has a disadvantage that circulating current flows through the power transformer and switching devices during freewheeling intervals. To decrease the circulating current to zero and thus to achieve zero-current switching, various snubbers, auxiliary circuits and/or clamps connected mostly at the secondary side of power transformer are applied [1] – [10]. The disconnection of the secondary windings is usually achieved by application of the reverse bias for the output rectifier or using controlled rectifier.  The optimal switching for IGBTs is zero-voltage turn-on and mainly zero-current turn-off due to elimination of the current tail influence, which has considerable high involvement in creation of the IGBT turn-off losses.  2. POWER CIRCUITS OF THE PROPOSED CONVERTER  To achieve the aims mentioned above, the topology of the following ZVZCS converter was designed.  The DC-DC converter shown in Fig.1 consists of high-frequency inverter, power transformer, output rectifier, output secondary switch and output filter. The main part of the converter includes high frequency full-bridge inverter consisting of the four ultrafast IGBT´s T1-T4 and freewheeling diodes D1-D4. The secondary winding of the high-frequency step-down power transformer TR is connected through a fast recovery rectifier D5, D6 and secondary switch T5 to output filter consisting of smoothing choke L0 and capacitor C0. The converter is controlled by modified pulse-width modulation (Fig.2), and consequently the zero-voltage turn-on and zero-current turn-off all of the transistors T1-T4 in the inverter are reached.    I n p u t  S o u r c e  T 1  D 3  u P  T 3  D 2  T 2  L S  D 5  i P  T 4  D 1  D 4  U  _  L O  C O  T 5  D C 1  T R  D O  R O  C C 1  D 6  C S 1  D S 1  C S 2  D S 2  D S 3   A u x i l i a r y  D C / D C  C o n v e r t e r  U O  U C C 1  U d  U S  U S  I 0  A E n e r g y  r e c o v e r y  c l a m p  T u r n - o f f  s n u b b e r A   Fig.1. Scheme of the proposed ZVZCS PWM DC-DC converter  100 Advances in Electrical and Electronic Engineering The semiconductor switch T5 in the secondary side is used to reset secondary and consequently also primary current. The transistor T5 operates with double switching frequency. At turn-off of the switch T5 the energy stored in leakage inductance is clamped by DC1 and CC1 and then transferred trough auxiliary dc-dc converter to the input source. By using non-dissipative snubber to reduce turn-off losses of the transistor T5, the overall efficiency is increased.   3. OPERATION PRINCIPLE  The basic operation of the proposed soft switching converter has eight operating modes (intervals) within each half cycle. The switching diagram and operation waveforms are shown in Fig. 2.    iP  iD O  u P  u S iC S 1  iD  T 1 ,  T 2 T 3 , T 4 T 5  T 5  t0 t 1 t2  t3         t 4 t5     t6                   t 7  t8  U iD C 1  T 1,  T 2  T 5 iD 5 iD 6 iD O  iD 0 iD 5 iT 5 td IP  Iµ  U S U C C 1  U S  IT 5m  IC S = IT5 m /2  I Dm a x I LS m ax  I Dm in ID m a xID m in+I LS m ax 0  0  0  0  0  0  0  0  0  t t t t t t t t   Fig. 2 Operation waveforms of the converter  4. SIMULATION RESULTS  A simulation model in programme Orcad was created to verify the properties of the proposed converter. The simulations were made at input voltage U = 320V. Parameters: Transformer TR parameters: Turns ratio n = 6,  Magnetizing inductance Lm = 800 H, Leakage inductance LLP = 7 H. Snubber circuit parameters: Snubber capacitors CS1 = CS2= 56 nF, Snubber inductance LS = 5 H. Set value of clamp voltage UCC1 = 80 V  The following waveforms were obtained at resistive load. Fig.3 shows switch voltage uCE4 and switch current iC4+iD4 during turn-on and turn-off of the transistor T4 in the converter. The switch (transistor T4 including diode D4) is turned-on under zero-voltage because at turn-on of the transistor T4 its freewheeling diode D4 is in on state. Moreover the rate of rise of the collector current is limited by the leakage inductance LLP of the transformer.  The transistor turn-off losses are negligible because transistor T4 turns-off only small magnetizing current (about 1.5 Amp in this case) as can be seen in the Fig.3.              Tim e168. 0us 17 0.0 us 1 72. 0us 17 4.0u s 176 .0us 1 78.0 us 18 0.0u s1  IC(Z 4)- I(D4 ) 2   V(P 1)0A4A8A12A-3A1    > >-1 00V0V1 00V2 00V3 00V4 00V2  Fig. 3. Switch (transistor T4 + diode D4) voltage uCE4 and switch current iC4+iD4.  Collector-emitter voltage uDS and collector current iD of the secondary transistor T5 (bottom waveforms) is shown in Fig. 4. The secondary switch (transistor T5) is turned-on under zero-current due to influence of the leakage inductance of the transformer LLS reflected to the secondary side and snubber inductance LS.  The turn-off loss is reduced by snubber capacitors CS1 and CS1 acting as the non-dissipative snubber as it is evident in Fig. 4.              Time169u s 170us 1 71us 17 2us 17 3us 174 us 175u s 176us 1 77us 1 78usI(Rco llect or) V(M1: d)- V (M1:s )-20020406080100 Fig. 4. Collector-emitter voltage uDS and collector current iD of the secondary transistor T5         Rectified voltage ud and output diode current iD5 is shown in Fig. 5.  ZVZCS PWM DC-DC Converter with energy recovery clamp 101            Time178 us 180 us 182u s 18 4us 18 6us 18 8us 190 us 19 1usI( D5)0 A50 A100 ASEL >>V( UD)0 V50 V100 V Fig. 5. Rectified voltage ud (upper waveform) Output diode current iD5 (bottom waveform)  During commutation between secondary diode and output freewheeling diode the secondary voltage and accordingly rectified secondary voltage is zero.  At turn-off of the secondary switch T5 the secondary and also rectified voltage rises as a result of energy stored in leakage inductance. The over-voltage US can be maintained on acceptable value by proper design of the auxiliary dc-dc converter. Fig. 6 shows the snubber capacitor current at turn-on and turn-off of the secondary switch T5 (bottom waveform).              Time169us 170us 171us 172us 173us 174us 175us 176us 177us 178usI(Cs1)0A25A50A-20ASEL>>I(Rcollector) V(M1:d)- V(M1:s)050100 Fig. 6. Collector voltage uDS and collector current iD of the secondary transistor T5 (upper waveforms) Snubber capacitor current iCS1 (bottom waveform)   5. CONCLUSION  Soft switching and reduction of circulating currents in the proposed converter are achieved for full load range using the secondary side turn-off and energy recovery clamp in combination with modified PWM control. At proper design it is possible to utilize the magnetizing current of power transformer for charging or discharging output capacitances of the IGBT switches and thus zero-voltage turn-on of the IGBTs to achieve.  The IGBT transistors are turned-off almost under zero current. Only negligible magnetizing current of the power transformer is turned-off by IGBT transistors. The main task of the proposed secondary energy recovery clamp is the transfer the leakage inductance energy to the input source at turn-off of the secondary switch. Turn-off snubber is employed to improve turn-off process of the secondary switch. Using leakage inductance of the power transformer working as a turn-on snubber it is ensured zero current turn-on process of the secondary switch. Finally, it is possible to say, that IGBTs in the full bridge inverter operate at almost ideal switching conditions – ZV turn-on and ZC turn-off. Soft switching of the secondary switch and leakage inductance energy transfer to the input source is ensured by turn-off snubber and energy recovery clamp containing only non-dissipative components.   Acknowledgment  This work was supported by Research and Development Support Agency under project APVV-99-031205.   REFERENCES  [1] KIM E. S.,JOE K. Y., KYE M. H., KIM Y. H.,  YOON B. D.: An Improved Soft Switching PWM FB DC-DC Converter for Reducing Conduction Losses, in Record, IEEE PESC’96, Vol. I., pp. 651-656. [2] CHO J. G., RIM G. H., LEE F. C.: Zero Voltage and Zero Current Switching Full Bridge PWM Converter Using Secondary Active Clamp, in Record, IEEE PESC’ 96, Vol. I., pp. 657-663. [3] RINNE K. H., THEML K., MCCARTHY O.: An Improved Zero-Voltage and Zero-Current Switching Full Bridge Converter,” in Record, EPE’ 95, Vol. 2., pp. 725-730. [4] HORVÁTH M., BORKA J.: Welding Technology and Up-to-date Energy Converters. EDPE 2005 Conference, Dubrovnik, Croatia, September 24-26, 2005. CD-Proc. E05-06. [5] LEUCHTER J., BAUER P.: Analysis of Losses in the Power Indirect Converters. Circuits Theory Symposium, ISBN 80-7231-011-9, Brno, 2005, pp. 117-120, (in Czech). [6] TERE, A., FEO, I., PÁNIK, P: DC/DC Converters with Soft (ZVS) Switching. In Conf. Proc. ELEKTRO 2001, section - Electrical Engineering. Žilina 2001, Slovakia, pp. 82 – 90. [7] CHLEBIŠ, P.: Soft Switching Converters. Monograph, VŠB-TU Ostrava, Ostrava, 2004, ISBN 80-248-0643-6, 148 p. (in Czech) [8] HAMAR J., NAGY I.: Bi-directional Resonant Buck & Boost Converter. ELECTROMOTION, Romania, Oct.-Dec. 2001, Vol.8, No. 4, pp.189-195. [9] TRIP N. D.: A New Active Snubber for DC-DC Boost Converters. 8th International Conference on Engineering of Modern Electric System 102 Advances in Electrical and Electronic Engineering Proceedings, Section Electronics, Oradea, Romania, May 2005, pp.124-127. [10] DUDRIK, J., ŠPÁNIK, P., TRIP, N.-D.: Zero Voltage and Zero Current Switching Full-Bridge DC-DC Converter with Auxiliary Transformer. IEEE Trans. on Power Electronics, Vol.21, No.5, 2006, pp. 1328 – 1335. [11] MILLY, D., MAXIM, V.: Simulation and Analysis of Power Converter Input Currents. International Computer Science Conference, MicroCAD'98, February 25-26, Miskolc, Hungary, 1998, pp. 63 – 68. [12] CHO J. G., BAEK J. W., YOO D. W., LEE H. S., RIM G. H.: Novel Zero-Voltage and Zero-Current Switching (ZVZCS) Full Bridge PWM Converter Using Transformer Auxiliary Winding, in Record, IEEE PESC’97, Vol. I., pp. 227-232. [13] CHO J. G., BAEK J. W., JEONG CH. Y., RIM G. H.: Novel Zero-Voltage and Zero-Current Switching Full Bridge PWM Converter Using a Simple Auxiliary Circuit, IEEE Trans. on Industry Applications, Vol. 35, pp. 15-20, 1999. [14] LIU R.: Comparative Study of Snubber Circuits for DC-DC Converters Utilized in High Power Off-line Power Supply Applications, in Record, IEEE APEC 9´9, pp.821-826. [15] DUDRIK J. AND DZURKO P.: An Improved Soft-Switching Phase-Shifted PWM Full-Bridge DC-DC Converter in Record, EPE-PEMC 2´000 Proc., Vol. 2, 2000, Košice, pp. 65-69. [16] PETROV, S.: Expectations of Resonant Converters Utilization as Welding Power Sources. Schematics No. 7, July 2006, pp.30-33 (in Russian).  

ZVZCS PWM DC-DC converter with energy recovery clamp

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ZVZCS PWM DC-DC converter with energy recovery clamp

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