The modular multilevel converter(MMC)is the core component of flexible high voltage direct current(HVDC)transmission technology

the capacitor voltage balancing of MMC determines the stable operation of transmission systems. To solve this problem

several kinds of capacitor voltage balancing algorithms based on capacitor voltage sorting are analyzed. Considering the features of capacitor voltage balancing algorithms

an improved algorithm based on the incremental capacitor voltage balancing algorithm is proposed. With only one parameter—the voltage limit introduced

this algorithm can regulate both voltage fluctuation and switching frequency. A simulation model of MMC is developed in PSACAD/EMTDC

in which all four algorithms are realized

and the theoretical analysis is proved. The results show that the proposed algorithm can greatly reduce the switching frequency. When in the same situation of voltage fluctuation

a lower switching frequency implies it is a voltage balancing algorithm of better performance.