Investigation of control and applications of modular multilevel converter with sub-modular series IGBTs
Modular Multilevel Converter (MMC) has been an attractive option for power transmission and has been studied and used for HVDC applications. However, it still has limitations when the number of Sub-Modules per arm is large. To avoid the limitations and exploit the advantages, a method is proposed in this paper which integrates an MMC with series-connected IGBTs in each Sub-Module (SM). The proposed MMC is able to withstand a higher voltage with devices of lower voltage ratings. The series-connected IGBTs are self-balancing. Simulink and real-time simulations both show that, with the proposed method, series IGBTs are able to share a much higher MMC sub-module voltage and recover from voltage imbalances in a timely manner. The proposed series IGBT balancing method causes considerably less loss compared to RCD snubber circuit-based balancing methods.