Cost-Effective Capacitor Voltage Balancing Strategy for MMC with a Prediction-Based and Improved PD-PWM Combined Approach

Modular multilevel converters face a serious issue in maintaining stable operation due to the sub-module (SM) capacitor voltage imbalance. Both pulse rotation and voltage sorting methods, which are the two widely used techniques for SM capacitor voltage balancing control, have benefits and limitations in terms of implementation and maintenance. A sorting-assisted rotation method was suggested to solve the contradiction between the capacitor voltage balance effect and the converter switching frequency. In this paper, the efficiency and working frequency of the sorting method are optimized to reduce the dependence of the proposed method on hardware and reduce the burden on the controller. The proposed approach is efficient and reliable, as demonstrated by simulation and experimental findings.