Unified PWM control to minimize conduction losses under ZVS in the whole operating range of dual active bridge converters

The dual active bridge (DAB) topology has great advantages for high power dc-dc conversion, especially in applications that bidirectional power transfer is required. Characteristics of dual active bridge are studied while approximating the power transfer by considering the fundamental components. Switching modes for each working mode of DAB are confirmed base on the criteria that extending the soft switching range and minimizing the conduction losses. Unified pulse-width-modulation (PWM) control that minimizes the conduction losses and allows all switches to be operated under zero-voltage-switching (ZVS) in the whole load range is proposed. The optimal relative values of duty cycles used for the two full bridges and the phase-shift are derived with respect to minimize the conduction losses under ZVS range in the chosen switching mode by applying the method of Lagrange Multiplier Rule. A DAB converter is modeled in Saber and the efficiency improving is verified by the simulation results.