Model Predictive Control with Hybrid Variable Frequency and Phase-Shift Modulation Accounting for Implementation Constraints

The Dual-Active-Bridge (DAB) converter is widely used in power conversion applications such as electric vehicle (EV) charging and energy storage systems due to its bidirectional power transfer capability and high efficiency. However, conventional single phase-shift (SPS) modulation suffers from efficiency degradation at light loads and non-unity voltage gain conditions due to the loss of Zero-Voltage Switching (ZVS). This paper investigates the hybrid modulation of SPS and Variable Frequency Modulation (VFM) to extend the ZVS range and improve efficiency. The ZVS boundary conditions under VFM are derived, and the relationship between phase-shift, switching frequency, and soft-switching capability is examined. The implementation constraints, including dead-time effects and the maximum feasible switching frequency for ZVS, are also analyzed. A Model Predictive Control strategy is proposed to satisfy ZVS constraints, minimizing switching losses and enhancing efficiency. Simulation results demonstrate the effectiveness of the proposed approach, in which our proposed method achieves ZVS and shows improved performance at light loads.