Hybrid predictive control with simple linear control based circulating current suppression for modular multilevel converters

The modular multilevel converter (MMC) has become a promising topology for widespread power converter applications. However, an evident circulating current flowing between the phases will increase system losses and complicate the heatsink design. This paper proposes a novel hybrid model predictive control method for MMCs. This method utilizes an indirect structure MPC and a sorting algorithm to implement current tracking and capacitor voltages balancing, considerably resulting in reduced calculation burden. In addition, different from the conventional MPC solutions, we add a simple proportional-integral (PI) controller to suppress circulating current through modifying the submodule (SM) inserted number, which is parallel to the MPC loop. This hybrid control solution combines both advantages of MPC and linear control, evidently resulting in improved performance of circulating current. Finally, the MATLAB/Simulink results of an 11-level MMC system verify the effectiveness of the proposed solution.