Securing Full-load-range Zero Voltage Switching for A Dual Active Bridge Based Electric Vehicle Charger

Dual-active-bridge (DAB) circuit is an excellent candidate for a high-efficiency, high-power-density and bidirectional electric vehicle charger. Unlike other circuits employing resonant inductors and capacitors, DAB minimizes the usage of passive components. The challenge, however, lies in difficulty of securing zero voltage switching (ZVS) at light-to-medium load. This is utmost important not only to the efficiency but also eliminating the bridge-switch crosstalk during the hard switching-on thereby enhancing the system reliability. Systematically integrating SPS, dual-phase-shift (DPS) and triple-phase-shift (TPS) to secure full-load-range ZVS in EV chargers has not been seen and is the focus of this paper. This paper plots the ZVS boundary for the full-load range, categorizes all operations into eight modes and proposes a smooth transition among SPS, DPS and TPS for a 20kW EV battery charger. Experimental results on a SiC-based charger validated its effectiveness and the smooth transition for the output voltage of 200~450VDC and 0~20kW.