Bidirectional Resonant Converter for DC Microgrid Applications

Abstract

A bidirectional resonant converter is presented and verified in this paper for an electric vehicle battery charger/discharger system. The presented circuit can achieve forward and backward power operation, low switching losses on active devices, and wide output voltage operation. The circuit structure of the presented converter includes two resonant circuits on the primary and secondary sides of an isolated transformer. The frequency modulation approach is adopted to control the studied circuit. Owing to the resonant circuit characteristic, active devices for both forward (battery charge) and backward (battery discharge) power operation can be turned on at zero voltage switching. In order to implement a universal battery charger for different kinds of electric vehicle applications, the DC converter is demanded to have a wide output voltage range capability. The topology morphing between a full bridge resonant circuit and half bridge resonant circuit is selected to obtain high- and low-output voltage range operations so that the 200–500 V output voltage range is realized in the presented resonant converter. Compared to the conventional bidirectional converters, the proposed can be operated under a wide voltage range operation. In the end, a 1 kW laboratory prototype circuit is built, and experiments are provided to demonstrate the validity and performance of the presented bidirectional resonant converter.