Selection-based capacitor voltage balancing control for modular multilevel converters

The modular multilevel converter (MMC) is a promising topology for high-power converters. The capacitor voltage balancing method for the submodules (SMs) is one of the key technologies in terms of modular multilevel converters. Aiming at the problems of the large calculation burden and the high switching frequency in the traditional capacitor voltage balancing method, an improved balancing method based on a novel selection algorithm for MMCs is proposed in this paper. The proposed method can avoid the sorting operation of the arm SM voltages in each control cycle without reducing the control precision of the capacitor voltages. In addition, it greatly improves the sorting efficiency. Thus, a criterion for algorithm rerun is introduced, which makes the MMC controller avoid reordering the capacitor voltages and leave the control signals unchanged when the capacitor voltages experience small changes. Finally, simulation and experimental results confirm the feasibility and effectiveness of the proposed method.