Bidirectional Isolated DC/DC Dual-Active-Bridge Converters Optimum Soft-Switching Control Method for Electrical Vehicle Applications

Electrical vehicles (EV) are appropriate alternative to the conventional internal combustion engines. The conventional grid-connected EV chargers consist of an AC/DC power-factor-correction (PFC) converter, and an isolated DC/DC converter connected to the battery. The isolated DC/DC converter can be used as a bidirectional converter providing power to the grid in the peak hours. During the entire charging process of the EV battery, the voltage varies significantly, and the DC/DC converter should operate under wide input and output voltage range. In this paper, the bidirectional dual-active-bridge (DAB) converter with both full-bridge and half-bridge topologies is studied. In the light-load condition, the zero-voltage-switching (ZVS) cannot be attained. Thus, a switching control method with emphasis on variable frequency and duty-cycle (VFD) is suggested at light-loads to improve overall efficiency of the DAB converters. Simulation results verifies the accuracy of this method.