In this paper, a new control method for modular multilevel converters(MMCs) is proposed. The inner-loop circulating current control is using a model predictive controller instead of a traditional PI controller. In this controlling method, the reference voltage vector is obtained firstly according to the load current, which is the primary controlling objective. Then, the equivalent number of submodules(SMs) that should be inserted in the next sampling period is determined based on the principle of minimum voltage deviation of submodules. Finally, the equivalent number is adjusted to suppress the circulating current. Switching states obtained by comparing the adjusted equivalent number with a carrier wave will be applied to the switching devices. The simulation results performed in MATLAB/Simulink software verify the effectiveness of the proposed method.

circulating current suppression,model predictive control,modular multilevel converter,space vector modulation