6.6 kW High-Frequency Full-Bridge LLC DC/DC Converter with SiC MOSFETs

This paper presented a 6.6 kW high-frequency DC/DC converter with SiC MOSFETs for high-voltage output applications, such as EV chargers. LLC topology was used because primary switch zero-voltage-switching (ZVS) turn-on and secondary diode zero-current-switching (ZCS) turn-off can be implemented to improve efficiency and reduce EMI. The main purpose of this work is to investigate the performance of SiC devices at frequencies (500 kHz - 1 MHz). Both simulation and experimental results demonstrated the superior performance of SiC MOSFETs at high frequencies up to 1 MHz. With high switching frequency, the leakage inductance of the LLC transformer can be used without an extra resonant inductor, and the overall size of the converter is much reduced since a smaller EMI filter can also be used. Effects of PCB layout on parasitic capacitances and efficiency have been studied. Practical design guidelines for key parts, such as high-frequency LLC transformer, resonant capacitors, gate drivers and PCB layout have been detailed. Experimental results show that 98 % peak efficiency can be achieved with SiC power devices at 550 kHz and 6.6 kW output power.