Resonant and Soft-Switching Converters

Advances in power electronics in the last few decades have led to not only just improvements in power devices but also new concepts in converter topologies, modulations, and control strategies. In the 1970s, conventional pulse-width modulation (PWM) power converters were operated in a switched-mode operation. Due to the nonideal switching characteristics, power switches have to switch their currents within the turn-on and turn-off times under the hard-switching conditions, causing undesired voltage and current stresses. More importantly, hard switching would cause high power and heat dissipation, introducing many reliability problems. In order to reduce the switching losses and improve the conversion efficiency, various resonant and soft-switching techniques have been proposed and widely used in various power electronic applications. The basic concept is to introduce an extra circuit, utilize parasitic elements, and/or timing control to profile switching trajectories, so that the switches are switched softly. This chapter gives an overview of various resonant and soft-switching techniques, such as zero-voltage switching, zero-current switching, zero-voltage transition, series resonance, and parallel resonance. It will start from describing the basic principles of those techniques to their applications to various systems, such as DC-DC power conversion and DC-AC power conversion. The electromagnetic compatibility performance will also be addressed. The emphasis is placed on the basic operating principle and practicality of the converters without using much mathematical analysis.