Improved combined modulation strategy for dual active bridge converter in electrified vehicles

The dual active bridge (DAB) converter is ideally suited for electrified vehicle applications for its galvanic isolation, bidirectional power flow and inherent soft-switching capability. However, when conventional single-phase-shift (SPS) modulation is applied, zero-voltage switching operation is limited by wide voltage range of high voltage and low voltage batteries, especially under light load condition. A combined modulation strategy including triangular, trapezoidal and SPS modulation has been proposed to extend soft switching range by realizing zero-current switching. In this paper, the current stress of each modulation method is analyzed comprehensively. It is observed that the boundaries applied in the traditional combined modulation strategy result in higher current stress in some operation area. A new boundary between the trapezoidal and SPS modulation is proposed to improve the combined modulation strategy. Current stress is reduced considerably in the area between traditional boundary and the new boundary. Simulation results are provided to validate the proposed boundary.