A duty-cycle control method to ensure soft-switching operation of a high-power three-phase dual-active bridge converter

In this paper, a duty-cycle control (DCC) method for a three-phase dual-active bridge (DAB3) converter with snubber capacitors is proposed to ensure the zero-voltage switching (ZVS) operation over the whole operation range. Closed-form expressions for the proposed modulation scheme are derived. Furthermore, the equivalent circuit and mathematical model of the converter commutation process are presented and analyzed, based on which an analytical method to determine a suitable deadtime is given. Moreover, the minimum current for a successful commutation is suggested. A high power DAB3 converter model with snubber capacitor in parallel to each device has been established in simulation, the proposed commutation-current-constrained DCC method ensures the soft-switching operation over the whole operation range with obsolete auxiliary circuits. Applying the switching optimized IGCT devices, the DAB3 converter achieves a high efficiency for a wide operation range.