New modulation strategy combining phase shift and frequency variation for dual-active-bridge converter

This paper proposes a new modulation strategy for a dual-active-bridge converter. The target of the new strategy is to suppress the circulating current in the converter by minimizing the load angle. The soft-switching operational area is expanded by employing frequency variation together with phase shift modulation. Unlike published modulation methods based on frequency variation, the strategy proposed in this paper can operate under the light or heavy power transmission regardless of the frequency limitation as well as the voltage ratio. As confirmed by experiments, the new strategy can boost the overall efficiency by up to 7% compared to the conventional single-phase-shift method.