Analysis and Design of a Hybrid-Type Converter for Optimal Conversion Efficiency in Electric Vehicle Chargers

In this paper, a hybrid-type converter, which can overcome the drawbacks of the conventional phase-shifted full-bridge (PSFB) converter, such as narrow zero-voltage-switching range, conduction loss by circulating current, and large output filter inductor, is analyzed and evaluated. The hybrid-type converter discussed in this paper consists of the conventional PSFB converter with a full-bridge rectifier and a half-bridge LLC series-resonant converter (SRC) with a voltage-doubler rectifier (VDR), sharing the lagging-leg switches and integrating the VDR of LLC SRC into the node of the secondary-side rectifier in the PSFB converter. This rectifier structure allows the targeted hybrid-type converter to have the advantages of high efficiency and high power density by the modification of the output voltage of LLC SRC. This paper analyzes the operation principle and power distribution of the targeted hybrid-type converter. Based on the analysis, the optimal design of transformer and the control strategy with frequency and pulse-width modulation are presented. With the precise design and control, the conversion efficiency and power density can be increased. Its validity is confirmed by experimental results involving a 3.3-kW (250-450-V/7.33-A) prototype converter.