Why SPS: The Best Phase-Shift Modulation Scheme for DAB-DCX Converter

The dual active bridge (DAB) converter is widely utilized in solid-state transformer, DC microgrid system, and so on. The single-phase-shift (SPS) modulation scheme is commonly employed due to its simplicity. However, high reactive power and peak current occur when the voltage conversion ratio deviates from unity. Multi-degree-of-freedom (M-DOF) modulation schemes have been proposed to enhance the efficiency by minimizing the current stresses and expanding zero-voltage switching (ZVS) range, however, these M-DOF modulation schemes are intricate. Several literatures have also proposed dc-dc transformer (DCX) mode with SPS for DAB converter to enable unity gain. However, the best phase-shift modulation scheme for DAB-DCX converter is uncertain. Therefore, this paper presents a systematic analysis and optimization of typical modulation schemes. Firstly, the performance indices related to efficiency are introduced, and the optimization objectives of M-DOF modulation schemes are determined. Secondly, the optimal solutions of M-DOF schemes are obtained using analytical optimization algorithms, and all optimal solutions are evaluated by performance indices to decide the optimal modulation scheme. Finally, the effectiveness of the optimal modulation scheme is verified by a two-stage AC/DC converter experimental prototype.