Unilateral Asymmetric Triple Phase Shift Modulation Strategy for DAB Converter Compromising RMS Current and Soft-Switching Range

Asymmetric Duty Modulation (ADM) opens up new opportunities for DAB converter to improve steady-state performance. Triple phase shift (TPS) modulation, which belongs to symmetric duty modulation (SDM), can minimize the inductor RMS current. However, the soft-switching range is still limited at light load. A unilateral asymmetric triple phase shift (UATPS) modulation strategy combining ADM and SDM is proposed in this paper to reduce the RMS inductor current while expanding soft-switching range. Firstly, typical waveforms of UATPS are generated by combining ADM and SDM, and the steady-state characteristics are derived in time domain. Secondly, a mathematical model for optimization is established, and the global optimal solution is obtained based on the Karush-Kuhn-Tucker (KKT) condition, and the direct power control strategy of the UATPS is proposed. Finally, the experimental results verify the effectiveness of UATPS to improve the efficiency.