Securing Full-Power-Range Zero-Voltage Switching in Both Steady-State and Transient Operations for a Dual-Active-Bridge-Based Bidirectional 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 resonant circuits employing auxiliary inductors and capacitors, DAB minimizes the usage of passive components. The challenge, however, lies in the difficulty of securing zero-voltage switching (ZVS), particularly at light-to-medium load when using the conventional single-phase-shift (SPS) control. This is of utmost importance not only for the sake of the efficiency, but also for minimizing the switch-bridge crosstalk caused by the hard switching-ON, thereby enhancing the system reliability. Although dual-phase-shift (DPS) and triple-phase-shift (TPS) can be the answer, they do introduce side effects such as larger switching-OFF current. This article systematically integrates SPS, DPS, and TPS to maximize full-power ZVS range for both steady state and transient operations in EV chargers. This article plots ZVS boundaries over the full power range, categorizes all operations into nine modes, and proposes a smooth transition method among all operation modes. Dead band is also incorporated in the ZVS boundary setting. Experimental results on a SiC-based charger validate the effectiveness of this method of widening ZVS range for output voltage of 200-450 Vdc and power of 0-20 kW, achieving smooth transitions among various operation modes, and suppressing the switch crosstalk, thereby securing high charger reliability.