Circulating Current Suppression Strategy for Modular Multilevel Converters Based on Fast Model Predictive Control

The modular multilevel converter(MMC), due to its unique topological structure, has been a hot topic of research, especially on how to suppress the internal circulating current. Particularly when the voltage is low and the number of submodules is small, traditional models have poor predictive control for suppressing the circulating current. To improve the suppression ability of circulating current, a fast model predictive control strategy based on the combination of extended submodules is proposed. This method expands the number of submodule combinations from M+1 to 3M+1 without increasing computational complexity, and establishes output current prediction models, circulating current prediction models, and a unified value function. The experimental results show that the proposed method can effectively suppress circulating current while improving the waveform quality of MMC output current. In addition, the proposed method has a low computational burden, which make it easy to implement digitally.