Simplification of Model Predictive Control for Modular Multilevel Converter through Direct Voltage Level Selection

Abstract

Model predictive control (MPC) method has attracted the attention of researchers for modular multilevel converter (MMC). However, the computation burden of the controller can be very high by using a direct MPC (D-MPC) method, especially when the submodule (SM) number of MMC becomes large. A stepwise indirect MPC (SI-MPC) strategy is first presented in this paper combined with capacitor voltage sorting algorithm to reduce the considered switching states. Ac side current control and circulating current control are separated of SI-MPC. The capacitor voltage ripple is neglected in the discrete-time mathematical model of MMC with SI-MPC, therefore, a direct voltage level selection (DVLS) method can be further derived with the simplification of SI-MPC. The current control process of MMC is implemented by comparing the current control error with the predesigned error bands. Simulation results verified the theoretical analysis and effectiveness of the proposed methods.