A Novel Sliding-Discrete-Control-Set Modulated Model Predictive Control for Modular Multilevel Converter

Model predictive control (MPC) method has been recognized as one of the most promising technologies for the modular multilevel converter (MMC) due to the fast dynamic response and its simple realization. However, conventional finite control set (FCS) MPC methods for MMC are facing some challenges, such as high computation burden, poor steady-state performance, dependence on weighting factors, and variable switching frequency. In order to solve these problems, a novel sliding-discrete-control-set (SDCS) modulated MPC (MMPC) is proposed for MMC in this paper. Based on the adaptive search step in the output current control, only three control sets are evaluated in each period. In addition, the independent circulating current controller is applied in the proposed MMPC method. With the circulating current controller, the circulating currents are well regulated, and the arm capacitor voltage balancing is realized by circulating current injection. As a result, there is no weighting factor involved in the proposed MMPC method. Compared with the conventional MPC methods, the proposed method obtains a fixed switching frequency in each submodule (SM) and a low comparable computation burden. Simulation and experimental results verify the effectiveness of the proposed method.