Optimal Switching Sequence Model Predictive Control for Modular Multilevel Converter

Abstract

This paper proposes a new optimal switching sequence model predictive control method for modular multilevel converter (MMC). In this method, the common mode voltage (CMV) is cosidered, which makes the model more accurate. The proposed method realizes the optimization of multiple control objectives of output current tracking, circulating current suppression (CCS), and submodule voltage balancing. The sequence that allows the output current to track its reference value is calculated in the <inline-formula><tex-math notation="LaTeX">$\alpha -\beta$</tex-math></inline-formula> coordinate system. And the virtual vectors aim to suppress the circulating current without influencing the output current are inserted. Capacitor voltage balancing is achieved by redundant vectors selection and tranditional selection algorithm. These control objectives are calculated independently, thus weighting factor is not required. At the same time, the computation burden is reduced by restricting the voltage mutation. This method has a satisfactory dynamic response and steady-state performance, the simulation and experimental results are given to verify the effectiveness of the method.