Research on capacitance voltage balance of modular multilevel converter based on improved quick sorting method

In recent years, modular multilevel converter high-voltage direct-current (MMC-HVDC) transmission technology has been widely used and developed. The sub-module(SM)capacitance voltage imbalance in MMC results in a larger MMC switching frequency, switching losses, high capacitance voltage fluctuations and other issues. In order to obtain better dynamic performance and harmonic characteristics, the traditional quick sorting method is improved under the premise of selecting the coefficient of variation (CV) as the criterion. In order to avoid unnecessary switching action, the sorted by state and by incremental switching capacitor voltage balanced control strategy is proposed. By reducing the capacitor voltage switching frequency and switching losses, the stability of the power system is improved. PSCAD / EMTDC simulation verifies the correctness and validity of the proposed method.