The process of energy flow of modular multilevel converter (MMC) is analyzed in detail

the cause of energy fluctuation is discussed and it is pointed out that the peak value of energy fluctuation is inversely proportional to operating frequency. When MMC motor drive is operated at low frequency

the fluctuation of modular capacitor voltage is so large that the motor drive cannot work normally. To solve this problem

this paper presents a control scheme

by which a high frequency sinusoidal component is incorporated in the arms’ common-mode current and a high frequency square component in the output common-mode voltage simultaneously. Thus energy exchange between the upper arm and lower arm is realized to restrain voltage fluctuation.The experiment results show that the fluctuation of modular capacitor voltage is effectively restrained and the performance of the low frequency drive system is satisfactory.