A novel submodule capacitor voltage balancing scheme for hybrid cascaded multilevel converter by injection of zero sequence current

Multilevel converters with fault tolerant capability are getting increased importance in the HVDC systems. This paper describes the working principle and submodule capacitor voltage balancing issues of the Hybrid Cascaded Multilevel converter (HCMC). The converter involves lesser number of sub-modules and provides excellent DC side fault tolerant capability in an HVDC system. The paper analyzes the submodule capacitor voltage balancing issues associated with this converter. A novel submodule capacitor voltage balancing scheme for the HCMC by the injection of zero sequence current is proposed in this paper. The efficacy of the proposed scheme is verified with the help of simulation study done in PSCAD/EMTDC.