High-Efficiency Hybrid LLC Resonant Converter for On-Board Chargers of Plug-In Electric Vehicles

Abstract

This article proposes a hybrid LLC resonant converter with three modes of operation for on-board chargers of electric vehicles. The converter can operate as a full-bridge converter, dual-phase half-bridge LLC converter, or single-phase half-bridge LLC converter to improve efficiency at low-voltage and light-load conditions. Without using additional switches, the operation mode of the proposed converter is switched by different modulation schemes. Moreover, the resonant inductance for LLC operation can be reduced so as to be integrated into the transformers, resulting in an increase in the power density. During the operation of three modes, all the primary switches achieve zero-voltage switching, thus minimizing the switching losses. A 3.2-kW-rated prototype using GaN devices with a power density of 65 W/in3 has been designed and tested to verify the effectiveness of the converter. Experimental results have shown smooth and stable transitions among three modes. A flat efficiency curve with a peak efficiency of 98.5% at full load condition has been achieved.