Capacitor Voltage Balancing Control Algorithm for Modular Multilevel Converter Based on the Dynamic Tiered Sorting

DC voltage control for modular multilevel converter (MMC) not only needs to control the total DC voltage, but also must control the capacitor voltage balancing of each sub-module (SM). The sorting-based traditional capacitor voltage balancing control algorithm is simple and easy to implement, but it needs to sort the capacitor voltages of all SMs of the valve arm and has low calculation efficiency. In this paper, a novel capacitor voltage balancing control algorithm based on the dynamic tiered sorting is proposed. By dynamically layering all sub-modules (SMs) on the valve arm, the number of SMs participating in the sorting is greatly reduced. Finally, the proposed algorithm is applied to the electromagnetic transient program of ADPSS (Advanced Digital Power System Simulator, ADPSS), and the correctness and the effectiveness of the proposed algorithm are verified by the back-to-back MMC-HVDC simulation case. The results show that the proposed algorithm not only can achieve the same control effect as the traditional algorithm, maintain the stability of all SMs capacitor voltage on the valve arm, but also can greatly improve computational efficiency.