An isolated bi-directional soft-switched high-frequency-ac link DC-AC converter using SiC MOSFETs

An isolated bi-directional soft-switched DC-AC converter with high-frequency-AC (HFAC) link using Silicon Carbide (SiC) MOSFETs is presented in this paper. A unipolar-SPWM oriented modulation technique is proposed to enable the full-bridge (FB) stage to realize zero-voltage-switching (ZVS) and the cycloconverter stage to realize zero-current-switching (ZCS). Furthermore, the proposed modulation technique allows half of the switches in cycloconverter to work at line frequency (LF) instead of switching frequency, which significantly reduces switching loss. Because of SiC MOSFET´s low on-resistance and great switching performance under high frequency conditions, they are used for all the switches such to further reduce the switching loss and conduction loss. Thus the switching frequency can be pushed to a much higher level, i.e. 50-100 kHz, which largely reduces the profile of the transformer and inductor. Therefore, the power-density of the converter is highly improved. The advantages of utilizing SiC MOSFETs are validated by simulation and experimental results.