A Novel Capacitor Voltage Balancing Control Strategy for Modular Multilevel Converters

Abstract

In engineering applications, there are hundreds of sub-modules in modular multilevel converter high-voltage direct-current (MMC-HVDC) transmission system. Voltage equalization of SM capacitors is always a key technical problem for stable operation of MMC. In order to solve the problem of traditional capacitor voltage sorting, this paper adopts the idea of integer factorization to group the bridge arm modules. Due to the voltage imbalance between groups, a inter group voltage balancing method is proposed. And according to the number of grouping groups, different sorting methods are selected, so then the sorting operation and the requirement for the hardware of the system are reduced. Aiming at the problem of large switching loss caused by repeated switching of IGBT SM in traditional voltage equalization method, this paper introduces the retention coefficient to reduce the switching frequency and the loss of SM. Finally, a double-ended MMC-HVDC supplying active networks is built in Matlab/Simulink to verify the correctness and effectiveness of the proposed capacitor voltage equalization method.