In distributed power supply and distributed energy storage technologies, a bidirectional AC-DC converter is an important energy conversion device connecting AC-DC hybrid microgrids, and its performance index directly affects the overall performance and effect of hybrid microgrids. Compared with the two-stage topology, the single-stage dual active bridge (DAB) AC-DC converter removes the intermediate DC bus capacitance with a large capacitance value, reduces the conversion link, and has apparent power density and cost advantages. The traditional DAB AC-DC converter mainly adopts the modulation strategy of phase shift, which has the problems of high current stress and narrow soft-switching range. In addition, only adopting the phase shift control leads to the nonlinear relationship between the system input current and the shift ratio, increasing the control complexity. Therefore, this paper proposes a linearization-based minimum current stress control strategy for the converter to address the problems of modulation nonlinearity and high current stress in a single-stage dual active bridge AC-DC converter. This control strategy reduces the converter’s control complexity and current stress, ensuring a wide zero voltage switch (ZVS) range of the switching tubes.

Firstly, the switching characteristics of the extended phase-shift (EPS) modulation strategy are analyzed. For the nonlinearity between the input current and the shift ratio, the input current i_ac and the shift ratio D₁ are linearly related by introducing the phase shift index k and the maximum switching frequency f_smax. The expressions of the shift ratio D₁ and the switching frequency f_s are obtained combined with power factor correction. The switching characteristics of the EPS modulation strategy are analyzed. The trajectory of the phase-shift index k under the minimum current stress is obtained by the differential polarity method. Then, the expression of the shift ratio D₂ is obtained. Finally, the soft-switching ranges are analyzed for switch tubes S₂, S₅, and S₈. Except for the DC-side switch tube S₅, which is difficult to realize soft-switching in the small range under extreme light-load conditions, the other two switch tubes can realize ZVS in the wide range in other cases.

This paper verifies the proposed control strategy by combining simulation and experiment. Firstly, regarding simulations, the proposed control strategy can achieve the linearization between the input current and the shift ratio, effectively reducing the converter current stress. An experimental prototype is constructed with an AC 50 V input, DC 12 V output, and 100 W output power. The current stress is compared before and after optimization under different input voltages and the soft-switching realization under different load conditions. The control strategy effectively reduces the current stress of the converter while ensuring that the switching tubes have a wide ZVS turn-on range.