Reduced Switching Loss Based Cell Capacitor Voltage Balancing Strategy for MMC

Modular multilevel converter (MMC) is considered to be an efficient solution for high voltage and high power applications, like for high voltage DC transmission (HVDC) system. This is due to their inherent modular structure, usage of low voltage power devices, inherent distributed energy storage capability for each cell unit and the absence of DC link capacitor. Due to their above-mentioned advantages they are considered to be a suitable candidate for medium voltage and medium power <; 500 kW) application like for energy storage and DC microgrid applications as well. However, MMC has an inherent problem of cell capacitor voltage imbalance. To solve this issue a reduced switching loss-based cell capacitor voltage balancing strategy is proposed. The proposed strategy is based on the conventional sorting algorithm, which helps to reduce the switching losses considerably while maintaining the set capacitor voltage ripple. Detailed analytical analysis and simulation studies are carried out to show the efficacy of the proposed system for a 300 kVA system. Results show a considerable reduction in the total converter losses (40%) compared to the conventional scheme.