A Voltage Balancing Control Strategy for Modular Multi-level Converters Based on the Improved Sorting Algorithm

The half-bridge sub-module (HBSM) topology is the main topology of SM in modular multilevel converters (MMCs). Although the capacitor voltage balancing method based on the sorting algorithm can reduce the difference between the SM capacitor voltage in MMCs, it also increases the computational burden of MMC controllers. To address this problem, the distribution of all the SM capacitor voltage in the ordered voltage sequence of one MMC arm and the operational rules of SM are analyzed, the appropriate insert objectives are determined. The voltage balancing control strategy based on the sorting algorithm proposed in this paper obtains the ordered voltage sequence of one MMC arm without sorting the capacitor voltage of all the SMs in one MMC arm. It can reduce the number of comparisons between the SM capacitor voltage without changing the voltage balance effect. Finally, the effective of the proposed control method is verified in MATLAB/Simulink.