Abstract: Targeting the problem of phase-to--phase circulating current and submodule voltage fluctuation of modular multilevel converter（MMC）,the paper proposes a circulating current suppression strategy based on additional level model predictive control（MPC）. The additional compensation level is used to update the total number of the submodules in real time,so as to suppress the circulating current. At the same time,the phase voltage balancing and submodule equalization are used as the first voltage balancing control of the submodules,and then the voltage of the input submodules is sorted to obtain the second voltage balancing control. By analyzing the relationship between the bridge arm circulating current and bridge arm voltage of MMC as well as the effects of voltage fluctuation of the submodules,the strategy for the circulating current suppression and voltage balancing control of the submodules is proposed. Finally,a 31-level MMC system simulation model is built in Matlab/Simulink,and the results verify the feasibility and effectiveness of the proposed strategy.