Modular multilevel converters have the problem of three?phase current asymmetry and fluctuations in active and reactive power when the grid voltages are unbalanced. For this reason, the mathematical model for voltage imbalance in power grid under different control objectives is established, and a frequency reduction model predictive control strategy suitable for grid voltage imbalance is proposed, which realizes accurate tracking of positive and negative sequence currents, and then, this paper introduces frequency reduction factors to effectively reduce the switching frequency and reduce the switching loss of modular multilevel converters. An improved moving average algorithm is proposed when calculating the switching frequency, which effectively reduces the memory and calculation amount occupied by the switching frequency calculation. The simulation results verify the effectiveness of the proposed control strategy by building a simulation model in Matlab/Simulink.