Enhanced Efficiency of MV Hybrid MMC under Extended Modulation using Si/SiC devices

The hybrid modular multilevel converter (MMC) consist of series connected half-bridge submodules (HBSMs) and full-bridge subnodules (FBSMs) in each arms. The dc fault blocking capabilty of hybrid MMC along with better dc link utilization have gain more attention in high voltage direct current (HVDC) transmission sytem as well as medium voltage (MV) appplications. However, with lesser SM counts in MV hyrid MMC requires large filter requirement which can be further reduced by increasing the swicthing frequency. By utilization the silicon carbide (SiC) MOSFETs over silicon (Si) IGBT allows faster switching but on other hand it increases the converter cost by six to eight time. In this paper a Si/SiC based FBSM and Si based HBSM based hyrid MMC has been proposed along with novel control scheme which ensure to allocate all the high frequency switching fucntions to the SiC MOSFETs. Further, simualtion study and a comparative loss analaysis is carried out in this paper.