Design Consideration of Flying Capacitor Multilevel Inverters Using SiC MOSFETs

SiC-MOSFETs are expected as promising power switching devices from the view point of high-speed switching and lower on-state resistance. In the multilevel inverters, the number of switching devices in the main current path increases. Thus, lower on-state resistance of the SiC-MOSFETs is very useful to reduce conduction loss of the inverter. In addition, to reduce required capacitance of the flying capacitors, higher switching frequency operation is indispensable. From this point of view, the higher switching frequency in high power applications realized by the SiC-MOSFETs is very attractive. In this way, the SiC-MOSFETs can dramatically enhance the advantages of the flying capacitor multilevel inverters. In this paper, as a basis of design consideration for flying capacitor multilevel inverters using SiC-MOSFETs, various experimental investigations employing four different prototypes are carried out. The effect of the number of the output levels and thermal management are demonstrated. In addition, key issues in extension to higher voltage applications are investigated.