Hybrid Modulation Strategy for DC-Bias Current Mitigation in Dual Active Bridge Converters

The use of the dual active bridge (DAB) as an electronic power converter in electric vehicles has gained interest in recent years thanks to features such as bidirectional power flow, galvanic isolation, high efficiency, high power density, low component stress, among others. Phase-shift modulation schemes are widely used for DAB control, being the most basic of them the single phase shift (SPS), followed by modulations with increasing number of degrees of freedom such as the extended phase shift (EPS), dual phase shift (DPS) and triple phase shift (TPS). A relevant concern in DAB applications is the appearance of transient dc components in the transformer current which are generated by load disturbances and the resulting sudden changes in phase-shift. This de-bias current reduces the converter efficiency, induces higher current stress in semiconductor switches and increases the risk of failures due to the saturation of magnetic cores. This paper proposes the implementation of a hybrid modulation strategy which combines different phase shift modulation schemes to mitigate the dc bias of the transformer current under load impacts. The validation of the modulation scheme is done through simulation analysis with the PLECS software.