A fundamental optimal modulation strategy for DAB converters based on a unified phase-shift control model

This paper introduces the concept of fundamental phase shift to provide a unified phase-shift control strategy description for power converters. It aims to simplify system control, reduce backflow power and improve operational efficiency. A Fourier-based Optimal Modulation Strategy (FOMS) is developed by decomposing transmitted active and reactive power for Dual-Active Bridge (DAB) converters. The unified mathematical model is applicable to Single Phase Shift (SPS), Extended Phase Shift (EPS), Dual Phase Shift (DPS) and Triple Phase Shift (TPS) modulation schemes. Theoretical analysis and simulation results indicate that under FOMS control, circulating harmonic components during constant active-power transmission are eliminated, significantly reducing the RMS value of inductor current. This RMS reduction diminishes backflow, thereby increasing overall converter efficiency. In all four modulation schemes and operating modes, backflow power is markedly reduced, and the system efficiency under the proposed FOMS can reach up to 95%. The proposed method simplifies implementation across different modulation strategies, offering a practical and efficient solution for power-electronics engineering. This study delivers valuable insights for optimising DAB converters and contributes to the progress of electric energy conversion technologies.