A Hybrid Modulation Strategy Providing Lower Inductor Current for the DAB Converter With the Aid of DC Blocking Capacitors

For the dual active bridge converter, the single phase shift (SPS) modulation strategy is simple and effective for controlling the transmission power. However, when the voltage varies widely, it is hard to realize soft switching and the circulating power increases dramatically, which results in the increased current stress and reduced efficiency. Thus, a hybrid modulation strategy is proposed in this article, whose main idea is to introduce a voltage offset across the dc blocking capacitors in both sides, and the converter can switch between different operating modes to lower the inductor current according to different operating conditions. Operational principle of the proposed modulation is introduced, and the normalized root-mean-square values of the inductor current in different working modes are derived mathematically, which leads to the selection criterion among different operating modes. The proposed scheme retains the simplicity of the conventional SPS strategy and improves the efficiency over wide voltage range and wide load range without complicating the topology structure. Finally, the performance of the proposed modulation is verified by the experimental results.