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A True ZCZVT Commutation Cell for PWM Converters Carlos Marcelo De Oliveira Stein, Student Member, IEEE, and Hélio Leaes Hey, Member, IEEE

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A True ZCZVT Commutation Cell for PWM Converters Carlos Marcelo De Oliveira Stein, Student Member, IEEE, and Hélio Leaes Hey, Member, IEEE IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000 185 A True ZCZVT Commutation Cell for PWM Converters Carlos Marcelo de Oliveira Stein, Student Member, IEEE, and Hélio Leaes Hey, Member, IEEE Abstract—This paper introduces a true zero-current and disadvantages as mentioned in [7] and [22]. Recently, an zero-voltage transition (ZCZVT) commutation cell for dc–dc improved ZCT technique was presented in [22]. In this pro- pulsewidth modulation (PWM) converters operating with an posal, all switches commutates under soft switching. How- input voltage less than half the output voltage. It provides zero-current switching (ZCS) and zero-voltage switching (ZVS) ever, the main switch and the main diode have a high peak simultaneously, at both turn on and turn off of the main switch current stresses. and ZVS for the main diode. The proposed soft-switching The aim of this paper is to introduce a true zero-current and technique is suitable for both minority and majority carrier zero-voltage transition (ZCZVT) commutation cell for dc–dc semiconductor devices and can be implemented in several dc–dc PWM converters. The commutation cell provides ZCS and ZVS PWM converters. The ZCZVT commutation cell is placed out of the power path, and, therefore, there are no voltage stresses on simultaneously, at both turn on and turn off of the main switches power semiconductor devices. The commutation cell consists of a and ZVS for the main diodes. few auxiliary devices, rated at low power, and it is only activated The proposed soft-switching technique is suitable for both during the main switch commutations. The ZCZVT commutation minority and majority carrier semiconductor devices, and can cell, applied to a boost converter, has been analyzed theoretically be implemented in any member of the dc–dc PWM converter and verified experimentally. A 1-kW boost converter operating at 40 kHz with an efficiency of 97.9% demonstrates the feasibility of family. The auxiliary shunt resonant network of the ZCZVT the proposed commutation cell. commutation cell is placed out of the power path, and, therefore, there is no voltage stresses on power semiconductor devices. Index Terms—High-performance dc–dc power conversion, IGBT’s, zero-current–zero-voltage switching (ZCZVS). The operation of the ZCZVT commutation cell applied to a boost converter is theoretically analyzed in Section II. A design guideline and a design example are presented in Section III. I. INTRODUCTION In Section IV, simulation and experimental results on a 1-kW HE OVERALL performance of pulsewidth modula- prototype using IGBT’s as both main and auxiliary switches are T tion (PWM) converters can be improved by the use of presented. The last section summarizes the conclusions drawn soft-switching techniques. These techniques allow operation from this investigation. at higher switching frequencies resulting in higher power densities without penalizing the efficiency [1]–[13]. II. PRINCIPLE OF OPERATION There are two main soft-switching approaches, that are the A. The ZCZVT PWM Boost Converter zero-current switching (ZCS) [1]–[8] and the zero-voltage switching (ZVS) [9]–[13]. The choice depends on the semi- Fig. 1(a) shows the ZCZVT PWM boost converter. It differs conductor device technology that will be used. For example, from a hard-switching PWM boost converter by the presence of MOSFET’s present better performance under ZVS. This is an additional shunt resonant network formed by two resonant because under ZCS the capacitive turn-on losses increase the capacitors and , a resonant inductor , a bidirectional switching losses and the electromagnetic interference (EMI). auxiliary switch and two auxiliary diodes, and On the other hand, insulated gate bipolar transistors (IGBT’s) . The main features of this topology are as follows. present better results under ZCS which can avoid the turn-off • There are no additional voltage stresses on power semi- losses caused by the tail current [3]. conductor devices. Nevertheless, the ZCS techniques proposed in the liter- • Commutation under ZCS and ZVS at both turn on and turn ature present some drawbacks such as significant voltage off for the main switch, whenever . stress on the main diode, which increases the conduction • Commutation under ZCS at turn on and under ZCS and losses, and the presence of the resonant inductor in se- ZVS at turn off for the auxiliary switch. ries with the main switch, which increases the magnetic • The output rectifier is commutated under ZVS and losses. These drawbacks are not present in the ZCT tech- its reverse recovery is minimized. nique, proposed in [8]. On the other hand, it presents other • The ZCZVT PWM commutation cell is placed out of the main power path, and it is activated during the switching transitions only. Manuscript received February 5, 1998; revised June 29, 1999. Recommended by Associate Editor, J. Thottuvelil. The authors are with the Federal University of Santa Maria, B. Operation Principles UFSM-CT-DELC, 97105-900 Santa Maria, RS, Brazil (e-mail: [email protected]). To simplify the analysis, the input filter inductance and the Publisher Item Identifier S 0885-8993(00)00382-3. output filter capacitor are assumed large enough, and, there- 0885–8993/00$10.00 © 2000 IEEE 186 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000 Fig. 1. ZCZVT PWM boost converter. Fig. 2. Operation stages. fore, the input current and the output voltage of the converter way until it reaches . At this time, the diode turns on. are considered constant over one switching cycle. The simpli- The resonant inductor current and the resonant capacitor fied circuit diagram is presented in Fig. 1(b). As shown in Fig. 2, voltage can be expressed as follows: 14 operating stages exist during one switching cycle, which are described as follows. (1) Stage 1— : The active switches are off, and the input current flows through the output rectifier . During this stage, the resonant capacitors voltages and are (2) clamped at ( for ) and , respectively. Stage 2— : At , the auxiliary switch is turned where on under ZCS. The current increases due to the resonance between and . The voltage evolves in a resonant and DE OLIVEIRA STEIN AND HEY: TRUE ZCZVT COMMUTATION CELL FOR PWM CONVERTERS 187 Fig. 3. Theoretical waveforms. The duration of this resonant stage is equal to where (3) and The duration of this resonant stage is defined by Stage 3— : During this stage, the current in- creases linearly up to , when the output rectifier is (8) turned off under ZCS and ZVS. The resonant inductor current is given by Stage 5— : The current decreases linearly until it reaches , when is turned off. To achieve soft (4) commutation for the main switch , its turn-on signal should be applied while the diode is conducting. The inductor where is when . The time interval of this stage current can be expressed as is given by (9) (5) where is when . The time interval of this stage is equal to Stage 4— : The current continues to increase due to the resonance between and . When the voltage reaches zero, the diode turns on. The resonant in- (10) ductor current and the resonant capacitor voltage can be expressed as follows: Stage 6— : At , the main switch is turned on under ZCS and ZVS condition. The current continues to ramp down until it reaches zero and the current through main (6) switch reaches . The resonant inductor current is given by (7) (11) 188 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000 Fig. 4. Relationship between k and k with k as parameter. The time interval of this stage is equal to The time interval of this stage is equal to (12) (18) Stage 7— : The capacitor and the inductor form a half-cycle resonance through the main switch and the Stage 10— : During this stage, the diode is on diode , which reverses the polarity of the voltage . and the main switch can be turned off under ZCS and ZVS. During this stage, the auxiliary switch can be turned off When reaches the input current again, the diode turns under ZCS and ZVS conditions. The resonant inductor current off. The resonant inductor current and the resonant ca- and the resonant capacitor voltage can be ex- pacitor voltage can be expressed as follows: pressed as follows: (19) (13) (20) (14) where is when . The time interval of this The time interval of this stage is equal to stage is equal to (15) (21) Stage 8— : The operation of the circuit at this stage is similar to that of the hard-switching PWM boost converter. Stage 11— : At , the resonant capacitor voltage The input current flows through the main switch . begins to increase due to the resonance between , Stage 9— : At , is turned on again under ZCS. and . When the resonant capacitor voltage As the current increases due to the resonance between reaches the diode turns on. The resonant inductor cur- and , the current through the main switch decreases rent and the resonant capacitors voltages and at the same rate since the sum of the two is equal to input current can be expressed as follows: . This stage ends when the current through the main switch reaches zero. At this time, the diode turns on again. The res- onant inductor current and the resonant capacitor voltage can be expressed as follows: (22) (16) (17) (23) DE OLIVEIRA STEIN AND HEY: TRUE ZCZVT COMMUTATION CELL FOR PWM CONVERTERS 189 (30) (24) where is when (31) where is when . The time interval of this stage is equal to (32) and where is when . Stage 14— : During this stage, the capacitor is linearly charged up to by the input current. At this moment the output rectifier turns on, beginning another switching The time interval of this stage is equal to cycle.
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