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 microinverters, this article proposes a quasi-single-stage discrete capacitor resonant dual active bridge (DAB) converter. The converter introduces a pseudobus 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 pseudobus 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 multimode 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.