Dual-Side Asymmetric Duty Modulation Based on Accurate Soft-Switching Characteristics Modeling for DAB-Based DC Microgrid

As the key equipment connecting the dc bus and the energy storage port in dc microgrid system, research on the dual active bridge (DAB) characteristics is of great significance. Due to the fixed 50% duty ratio of trigger pulses, phase-shift control may lead to a restricted soft-switching range and excessive peak current especially under light-load conditions. Therefore, in this article, dual-side asymmetric duty modulation (DADM) is proposed to avoid these problems effectively. First of all, for different DADM modes, operation principles, power characteristics, current characteristics, and soft-switching characteristics are depicted comprehensively. Second, influences of junction capacitance
${C} _{\text {oss}}$
and dead-band time
${t} _{\text {db}}$
are taken into consideration and mathematical modeling of the resonant process for different switching conditions is also analyzed in detail. Accurate zero-voltage-switching (ZVS) boundaries are established and conditions with all switches ZVS can be achieved. Third, based on all switches ZVS, an rms current minimization scheme is proposed to improve the efficiency performance. Finally, comprehensive comparisons among the proposed DADM and other existing modulation schemes are provided. The proposed DADM can achieve the lowest peak current, lowest rms current, and widest soft-switching range. A DAB-based prototype is established and, the effectiveness and correctness of the proposed method can be verified.