Quasi-Single-Stage Micro-Inverter Based on Discrete Capacitor Resonant DAB and its Control Strategy

To satisfy the high-performance power conversion requirements of photovoltaic micro-inverters, this paper proposes a quasi-single-stage discrete capacitor resonant DAB converter. The converter introduces a pseudo bus and combines the transformer leakage inductance with the discrete capacitors on the DAB secondary side to form a resonant circuit. The resonant operation generates a sinusoidal half-wave at twice grid frequency on the pseudo bus and achieved AC output through periodic inversion. On this basis, a modeling method based on single-sided Fourier equivalent transform is proposed, which effectively reduces the modeling complexity of the quasi-single-stage resonant DAB and ensures model accuracy. And, a unified representation of the output currents in three operation modes is derived, which facilitates continuous current regulation under multi-mode switching. In order to achieve favorable system power control, the performance of the converter under different operating modes are analyzed, and a dual-phase-shift variable frequency modulation strategy with high efficiency and low backflow power is studied. Finally, the proposed converter and its control strategy are validated through experiments.