Optimization of the auxiliary switch components in a flying capacitor ZVS PWM converters

A family of PWM converters with an Auxiliary Switch Assisted Soft Switcher (AASS) is studied. The basic AASS cell includes an inductor connected in series with the auxiliary switch of the converter, a capacitor connected in parallel with the main switch or main diode of the converter and an additional capacitor (designated a ´Flying´ capacitor) connected through an auxiliary diode parallel to the inductor and through an extra auxiliary diode parallel to the main diode of the converter. The unified analysis of steady-state processes in a generalized AASS converter, carried out in this investigation, is applicable to various PWM topologies. It is shown that AASS ensures soft switching of all power devices and that the voltage and current stresses are not appreciably higher than in the corresponding hard switched PWM topologies. A design procedure for optimization of AASS parameters is developed. Experimental investigation (a Boost DC-DC converter 130/380 V, 1.1 kW, switching frequency 100...160 kHz) confirmed the results of the theoretical analysis.