<p>The low-frequency performance of Modular Multilevel Converters (MMC) is an important indicator of variable frequency drive systems. When the motor runs at low frequencies or low speeds, abnormal pulsation of the Sub-Module (SM) capacitors voltage will directly affect the stable operation of the MMC variable frequency drive system. In this paper, to decrease the abnormal pulsation of SM capacitors voltage in MMC, the reasons for the voltage fluctuation were analyzed, and two control strategies based on high-frequency injection methods were consequently proposed. One is the improved Model Predictive Control (MPC) strategy based on the traditional output current prediction model, which introduces the prediction model of the voltage difference between the upper and lower arms, and the prediction model of common mode voltage. The other is an optimized cascade control strategy, which adds independent control of each phase voltage and balance control of the arms voltage on the basis of traditional output current control, and also uses deadbeat current control instead of current PI control, SM voltage sorting instead of traditional P control. The effectiveness of the above control strategies have been verified through simulation and experiments, and the dynamic and steady-state performance of MMC under the two control strategies during low-frequency operation were further compared.</p>