Coordinated Control Strategy of Capacitor Voltage and Circulation Suppression in MMC-HVDC

The modularized multilevel converter(MMC), which is widely used in HVDC transmission system. The unbalance of capacitor voltage and interphase circulation in submodules is often occurred when the carrier phase-shift modulation technology is used, which would result in distortion of output voltage and affect the operation performance of MMC system. Based on the mathematical model of MMC, this paper proposes a coordinated control strategy based on PI control and repetitive control. After establishing the simulation model of the MMC system coordination control strategy in MATLAB/Simulink, the parameters were set, and the system simulation was carried out. The results showed that the coordinated control strategy of PI control and repetitive control can better balance the capacitor voltage of the submodule(SM), restrain the negative sequence circulation of double frequency, and improve the output voltage quality.