A novel primary-side-assisted soft-switching and fault-tolerance of a high-frequency-link inverter for renewable-energy systems

A modulation-based soft-switching scheme is outlined for a high-frequency-link (HFL) inverter, which comprises a front-end HF isolated dc/ac converter followed by an ac/dc converter and an ac/ac converter. The proposed zero-voltage and zero-current switching (ZVZCS) scheme provides loss mitigation for all three legs of the ac/ac converter. Because the output of the ac/dc converter is pulsating-dc in nature, it retains the multi-phase encoded information generated by the dc/ac converter´s sinusoidal modulation. Although the inverter only needs a two-phase HF transformer to generate a three-phase output, a third phase is used to yield higher fault-tolerance. That is, in case of a fault in one of the phases of the HF transformer, two other phases can carry on nominal operation. The results are verified using simulation and experiments on a 2 kW, 40 V/208 V three-phase inverter.