Contents I. Introduction
The Pulsewidth Modulation (PWM) technique is praised for its high power capability, fast transient response, and ease of control. The PWM dc-dc converters have been also widely used in industry. For minimization of size and weight, increasing switching frequency in the PWM converter is required. However, increasing switching frequency will result in the more switching losses and electromagnetic interference (EMI). Recently, for improving this problem, a number of soft-switching PWM techniques were proposed aimed at combining desirable features of both the conventional PWM and resonant techniques [1]–[9]. The zero-voltage-switching (ZVS) approaches are desirable for a majority of carrier semiconductor devices such as metal-oxide-semiconductor field-effect transistor (MOSFETs), since the turn-on loss caused by the output capacitance is large. The zero-current-switching (ZCS) approaches are suitable for the minority of carrier semiconductor devices such as insulated gate bipolar transistors (IGBTs), since the turn-off loss is large due to the current tail characteristics. In recent year, IGBTs are preferred for high-power application, since IGBTs have a higher voltage rating and higher power density compared with MOSFETs. However, IGBTs are relatively slow in switching speed, so the switching losses and the high frequency of operation are two well-known problems [5]. In order to overcome previous problems, a number of ZCS-PWM techniques have been proposed [6]–[9]. In the approaches proposed in [6] and [7], ZCS of the active switches is achieved by using a resonant inductor in series with the main switch and a resonant capacitor in series with the auxiliary switch. Unfortunately, switching losses in the approaches proposed in [6] [7] can be reduced only at the expense of much increased current stresses of the main switch, which leads to a substantial increase in conduction loss. This phenomenon is eliminated in the approaches proposed in [8] [9] by the resonating current for ZCS flows only through the auxiliary circuit, thus, the current stress of the main switch is eliminated. But it presents two power diodes in the power transfer path, which increases conduction losses of the diodes. A new ZCS PWM commutation cell is proposed that improves the drawbacks of the previously proposed ZCS PWM converters. The proposed commutation cell provides ZCS condition for both the main switches and auxiliary switch, and the all passive semiconductor devices in the ZCS-PWM converters operate at ZVS turn on and turn off. Since the circulating current for the soft switching flows only through the auxiliary circuit, the conduction loss and current stress of the main switch are minimized. A new family of DC/DC PWM converters based on the proposed ZCS PWM commutation cell is proposed. Besides operating at constant frequency and with reduced commutation losses, these new converters have no additional current stress and conduction losses in the main switch in comparison to the hard-switching converter counterpart. The new family of ZCS-PWM converters is suitable for high-power application using IGBTs. Among the new family of dc/dc converters, principle of operation, theoretical analysis, and experimental results of the new ZCS-PWM boost converter, rated 1 kW and operating at 40 kHz, are provided here to verify the performance of this new family of converters.
