ZVS Enhancement of Dual Active Bridge Converter Using Series Connected Inductors for EV Battery Charging Application

Dual Active Bridge (DAB) converter is a promising candidate for isolated dc-dc converter stage in an on-board electric vehicle (EV) battery charger. DAB converter’s zero voltage switching (ZVS) range is dependent on the voltage conversion gain (VCG) and load conditions of the converter. When DAB converter is utilized in battery charging applications, the VCG varies over the constant-current constant-voltage (CCCV) charging cycle and thus limiting the ZVS range. Several control and hardware methods exist that improve the ZVS range. Advanced control methods compared to single phase shift (SPS) control enhance the ZVS range at the cost of computational complexity. Hardware methods such as tap changing transformer changes the leakage inductance constantly and also decreases the power density of DAB converter. In this paper, a hardware method on varying leakage inductance is proposed to enhance the ZVS range during CC-CV charging cycle. The equivalent inductance is varied by connecting an inductor in series with the transformer windings and optimally switched into the circuit based on load. The proposed method is analytically studied with a design example and verified through simulation results.