Evaluation of Medium Voltage SiC Flying Capacitor Converter and Modular Multilevel Converter

With the commercialization of wide-bandgap (WBG) semiconductor devices, the design strategy of medium-voltage inverters has to change. This paper compares SiC MOSFET in two medium-voltage multilevel inverters: Flying Capacitor Converter (FCC) and Modular Multilevel Converter (MMC). Both topologies have a single DC source and floating capacitors. Capacitor selection and power loss analysis are compared and the simulation results of both topologies are presented. The result shows that FCC is superior in terms of power density because the capacitor size of the FCC is directly related to the switching frequency whereas the capacitor size of the MMC is related to AC line frequency. FCC also has fewer switching devices and capacitors, and better utilization of switching devices. On the other hand, the MMC has better modularity, lower capacitor current, lower total harmonic distortion (THD), and a more mature voltage-balance strategy. The efficiency of both topologies is comparable.