A Hybrid 4-quadrant Switch for AC Power Conversion

Realization of 4-quadrant switches for AC power conversion applications using typical single-quadrant semiconductors like MOSFETs and IGBTs along with diodes is a persistent problem. The classical topology of using a single-quadrant switch across the DC terminals of a full bridge rectifier has excessive conduction losses arising from three semiconductors in the current conduction path. A more preferred realization that uses two series-connected single-quadrant switches, each with an anti-parallel diode has reduced conduction losses, but suffers from the need for a careful commutation sequence to prevent voltage and/or current overshoots during switching. Moreover, the voltage blocking capability of discrete devices places an upper bound in power for high voltage applications. These issues pose a significant barrier that has prevented the commercial application of matrix converters, AC to AC converters and solid state circuit breakers for AC systems. In this paper, a hybrid approach that is based on the use of a capacitor along with diodes and transistors to realize a solid state modular AC switch is presented. The paper presents the operating principle, design considerations and hardware verification along with a comparison of conventional approaches.