Power-Loss Analysis and Efficiency Maximization of a Silicon-Carbide MOSFET-Based Three-Phase 10-kW Bidirectional EV Charger Using Variable-DC-Bus Control

Abstract

It is expected that wide-bandgap devices like silicon-carbide MOSFETs and gallium-nitride HEMTs could replace Si devices in power electronics converters to reach higher system efficiency. This paper adopts the conventional half-bridge LLC topology to realize a 10-kW all-SiC bidirectional charger used in electric vehicles. Though it is a well-known topology for the unidirectional charger, it has not been comprehensively explored for the bidirectional energy flow yet. A double-pulse-test (DPT) platform is utilized to provide accurate power losses. A state-space model is built to obtain accurate switching current waveforms, which is eventually combined with the DPT results to accurately predict the system efficiency. Based on this model, to further enhance the system efficiency, the dc-bus voltage is varied with LLC dc/dc converter running at the resonant frequency through the whole power range. Experimental results validated that the proposed approach could realize the bidirectional power flow. By varying the dc-bus voltage, the V2G and G2V modes reach ~96 % wall-to-battery efficiency.