Modified unified PWM control to operate the dual active bridge converters under ZVS in the whole load range

The dual active bridge (DAB) topology has great advantages for high power dc-dc conversion, especially in applications that bidirectional power transfer is required. In previous work, the unified pulse-width-modulation (PWM) control strategy was proposed, to minimize the conduction losses and allow all switches to be operated under zero-voltage-switching (ZVS) in the whole load range. Considering resonant transitions between the leakage inductance and the nonlinear parasitic output capacitances of semiconductor switches, the unified PWM control is modified to extend ZVS operation to the whole load range in practical applications. The minimum commutation current required to complete the resonant transition within the dead-time interval is calculated and the optimal relative values of duty cycles used for the two full bridges and the phase-shift are derived. A DAB converter is modeled in Saber and the efficiency improving is verified by the simulation results.