Light-Load Efficiency Improvement of Single-Stage Microinverter With Online Iterative Trajectory Optimization Strategy

Due to the inherent intermittency of solar energy, photovoltaic (PV) microinverters (MIs) often operate under prolonged light-load conditions. To improve energy utilization, this paper proposes a novel online iterative trajectory optimization (OITO) strategy for the single-stage series resonant dual-active-bridge (DAB) MI to enhance the light-load efficiency. Through the zero-voltage switching (ZVS) condition analysis, the all-switch ZVS constraint is constructed. On this basis, a ZVS-constrained real-time iteration algorithm is developed to optimize inductor RMS current, with particular emphasis on minimizing the RMS current under light loads. By analyzing the constraint priorities and iteratively solving boundary equations with switching-frequency limits, the optimal trajectory of degrees of freedom (DOFs) is derived. Compared with conventional DAB MIs, the proposed strategy achieves a wider ZVS range while producing reduced inductor RMS current, which improves the light-load efficiency of the MIs. Accordingly, a GaN-based MI prototype is built, and the proposed strategy is validated, achieving a peak efficiency of 97.21%.