Wide-operating-range ZVS Optimization Method for Single-stage DAB Microinverters

Single-stage DAB microinverters are susceptible to ZVS failure under wide-load and time-varying grid voltage conditions, which significantly degrades conversion efficiency. To address this critical issue, an in-depth theoretical analysis of the ZVS boundaries for DAB microinverters under full operating conditions is conducted, and a wide-load dual-mode cooperative soft-switching strategy is proposed. First, based on extended phase shift modulation, the time-domain evolution of the leakage inductor current and the commutation mechanisms under different operating modes are thoroughly analyzed, and the analytical ZVS boundaries are derived. Comparative analysis reveals that a single modulation mode fails to cover the full-range soft-switching operations, whereas mode 2 and mode 3 exhibit significant complementary characteristics across different power and grid phase regions. Accordingly, a critical power threshold is extracted, and a multi-mode cooperative control strategy is proposed. By precisely matching both the macroscopic active power and the microscopic inductor current states, this strategy successfully eliminates transient disturbances during mode transitions. Finally, a 600 W experimental prototype is constructed for verification. Experimental results demonstrate that the proposed strategy substantially expands the soft-switching range, achieving a peak efficiency of 96.7% and reducing the grid current total harmonic distortion to 1.931%.