Abstract— This paper proposes a PWM inverter that allows the main switches to be turned on and off at zero voltage and zero current, respectively, with controlled di/dt and dv/dt rates. The reverse recovery losses of the main diodes are minimized, and the auxiliary switches are turned on and off in a ZCS mode. The main switches turning-on at zero current can reduce significantly the undesirable effects of the parasitic inductances related to the circuit layout. The commutation losses are practically reduced to zero and the EMI emission can also be minimized. The operation of the ZCZVS PWM Full-Bridge McMurray, using an auxiliary power supply to the control system, is analyzed, and design guidelines for the auxiliary commutation cell are recommended based on this analysis. Experimental results are presented to demonstrate the feasibility of the proposed 2kW inverter. I. INTRODUCTION With the growing development of power devices technology, switching mode power conversion moves towards high frequency operation, which can lead to high power density and fast dynamic response. For inverters, the operation at high frequency is required to reduce the audible noise, the volume and the weight of filters, as well as to improve output voltage quality. However, at high frequency operation, switching losses and electromagnetic interference (EMI) become significant and must be analyzed in detail. Power semiconductor devices commutate under two possible techniques: hard and soft. With hard switching, the devices are required to change their states (on and off), while they are subjected at both finite current and voltage values. High switching stresses produced by the overlapping of voltage and current result in high switching losses. To illustrate, the hard switching is shown in Fig. 1 (a). Soft switching techniques aim to reduce the mentioned overlap between voltage and current during the commutation. Thus it is possible to reduce switching losses, enabling high frequency operation and achieving higher power density. Soft switching techniques can be classified into two groups: zero voltage switching (ZVS) and zero current switching (ZCS) [1]. In the literature, several soft switching techniques have been proposed for PWM inverters, and nearly all of them operate with ZVS. Typical examples are the auxiliary resonant commutated pole inverters (ARCP) [1-3], the ZVS [4-7] and ZVT (Zero Voltage Transition) inverters [8]. To perform ZVS, the auxiliary commutation circuit only helps main switches turn-on, while snubber capacitors reduce turn-off losses. To illustrate, the current and voltage waveforms of a power switch with ZVS are shown in Fig. 1 (b). In some ZVS inverters, the load current charges the snubber capacitors at main switches turn-off, and as results, there is an important dependence between the load current value and the conduction time of the main diodes. Moreover, at high power application where minority carriers devices are usually employed, the turn-off losses caused by tail current cannot be totally avoided with ZVS technique [8]. Minority carriers devices, such as IGBT and MCT, present better performance with zero current switching, which can minimize substantially the mentioned turn-off losses. So, several ZCS techniques applied to PWM inverters are being investigated in the literature. However, main switches turn-on losses and the adverse effects of the main diodes reverse recovery were not totally solved yet. Fig. 1 (c) shows the ZCS commutation. In order to overcome the drawbacks of the above mentioned soft switching techniques, this paper proposes a new auxiliary commutation cell for PWM inverters, denominated Zero Current and Zero Voltage Transition (ZCZVT). It allows main switches commutations to happen simultaneously with zero voltage and zero current, at both turn-on and turn-off, and in addition it slows di/dt and dv/dt. So, the reverse recovery losses of the main diodes are minimized and the auxiliary switches are turned on and off at ZCS. The main switches turn-on at zero current can reduce significantly the undesired effects of the parasitic inductances related to the circuit layout. The commutation losses are virtually reduced to zero and the EMI emission can be reduced. The zero voltage and current switching is illustrated in Fig. 1 (d). The operation of the proposed ZCZVT commutation cell applied to a full-bridge PWM inverter is theoretically analyzed in Section II. Section III presents a design guidelines and an example. The command circuit strategy is presented in Section IV. The theoretical results obtained from a 2 kW ZCZVT full- bridge McMurray inverter are given in Section V. The last section summarizes the conclusions drawn from this investigation. A ZCZVT PWM Three-Level Full-Bridge McMurray Inverter Carlos A. Gallo, Fernando L. Tofoli, Ernane A. A. Coelho, Luiz Carlos de Freitas, Valdeir J. Farias, João Batista Vieira Jr. Federal University of Uberlândia Department Of Electrical Engineering Av. João Naves de Ávila, 2160, Campus Santa Mônica, Bloco "3N" CEP 38400-902, Uberlândia, MG, Brazil, +55-34-32394166 E-mail: batista@ufu.br 2004 35th Annual IEEE Power Electronics Specialists Conference Aachen, Germany, 2004 0-7803-8399-0/04/$20.00 ©2004 IEEE. 4803