Extended soft switching operation of three-phase dual active bridge converters with unbalanced transformer impedances

Unbalanced transformer impedances for three-phase dual active bridge (DAB) converters cause different zero voltage switching (ZVS) boundaries for each phase leg, which limit the converter soft switching regions. This paper uses harmonic analysis to demonstrate how asymmetrical PSSW modulation can be applied to shape each phase leg's ZVS boundary. The conclusions from the analysis provide guidelines to extend the ZVS range of practical three-phase DABs as is experimentally verified on a laboratory prototype.