MMC capacitor voltage decoupling and balancing controls

Summary form only given. A Modular Multilevel Converter (MMC) control system based on converter energy storage is proposed in this paper for two different control modes: active power and dc voltage. The proposed control system decouples the sub-module (SM) capacitor voltages from the dc bus voltage. One of the practical applications is the management of active redundant SMs. A practical HVDC system with 401-level MMCs including 10% redundancy in MMC SMs, is used for validating and demonstrating the advantages of the proposed control system. This paper also presents a novel capacitor voltage balancing control based on max-min functions. It is used to drastically reduce the number of switchings for each SM and enhances computational efficiency.