Switching condition and loss modeling of GaN-based dual active bridge converter for PHEV charger

The dual active bridge converter is examined as the DC/DC stage of a battery charger for the plug-in hybrid electric vehicle where both load voltage and load current have very wide operating range. The load current for sinusoidal charging scheme could swing down to zero. To optimize the battery charger under this charging scheme, a DAB loss model over wide load range is needed. Traditional DAB analysis focus on the loss model within the full zero-voltage-switching (ZVS) region where all DAB switches have ZVS. Beyond this region, the switching conditions of the DAB switches are more complicated with mixed states of ZVS, hard-switching (HS), or partial zero-voltage-switching (PZVS). This paper investigates the DAB operating and switching conditions with the consideration of the resonant transition and deatime, and identified the boundaries among hard-switching, partial zero-voltage-switching, and zero-voltage-switching conditions. Based on this, accurate DAB loss model can be derived. The loss model was verified by experimental measurement of a 500 kHz GaN DAB converter.