An isolated bi-directional high-frequency-AC link DC-AC converter using hybrid SiC switches with carrier-based unipolar modulation technique

A novel isolated bi-directional soft-switched high-frequency-AC (HFAC) link DC-AC converter using SiC MOSFET and IGBT hybrid switches is presented in this paper. The DC-AC converter is composed of a full-bridge (FB) inverter cascaded with a cycloconverter through a high-frequency transformer. In order to increase the converter efficiency, and to push the transformer frequency to 50-100 kHz, SiC MOSFETs are preferable devices compared to the traditional IGBTs or SCRs. A unipolar-SPWM-oriented modulation technique is proposed to realize zero-voltage-switching (ZVS) for FB and zero-current-switching (ZCS) for cycloconverter, and to suppress the voltage spikes introduced by the transformer leakage inductance as well. With the novel modulation technique, half of the AC switches in the cycloconverter work under transformer frequency and the rest work at line frequency (60 Hz). Therefore a SiC-IGBT hybrid switch structure is proposed for the cycloconverter. Simulation model and a 400 VDC to 240 VAC, 3 kW prototype have been developed to validate the effectiveness and performance of the proposed unipolar soft-switching modulation technique and the hybrid switch structure.