Circulating current suppression control for modular multilevel converters based on restricted self-redundant states prediction

摘要

Circulating current exists among phases or between the DC link and the three phases in a modular multilevel converter (MMC). Suppression control of the alternating components in circulating current is a critical issue for the stable and efficient operation of an MMC. Due to the redundancy and symmetry of MMCs, some of the self-redundant states of MMCs can be used to suppress the alternating components in circulating current without affecting the output performance of the converter. In this paper, a theoretical derivation of the boundary of redundant states is given. Then a suppression strategy for circulating current is proposed based on prediction control and the boundary of redundant states. The selection range of the redundant states is narrowed in this case, which reduces the computation burden when compared to the original method and ensures excellent performance in the suppression of circulating current. Simulations and experiments are carried out to verify the effectiveness of the proposed strategy.