Resonant and soft-switching converters

This chapter covers the basic technology of resonant and soft-switching converters. Prior to the availability of fully controllable power switches, thyristors were the major power devices used in power electronic circuits. The resonant switch is said to operate in half-wave mode. If a diode is connected in anti-parallel with the unidirectional switch, the switch current can flow in both directions. Quasi-resonant converters (QRCs) can be considered as a hybrid of resonant and PWM converters. The underlying principle is to replace the power switch in PWM converters with the resonant switch. Zero-current switching (ZCS) can eliminate the switching losses at turn off and reduce the switching losses at turn on. As a relatively large capacitor is connected across the output diode during resonance, the converter operation becomes insensitive to the diode's junction capacitance. Resonant dc link inverter with low voltage stress consists of a front-end resonant converter that can pull the dc link voltage down just before any inverter switching. This resonant dc circuit serves as an interface between the dc power supply and the inverter. © 2011 Elsevier Inc. All rights reserved.