A novel distributed control strategy for modular multilevel converters

The flexibility and expandability of the Modular Multilevel Converters (MMCs) from the modularized hardware may be reduced because of the conventional centralized control strategies. A distributed control architecture that is capable of assigning individual control task to distributed local controllers is proposed in this paper to address this issue. Although a central controller dealing with the output and differential current regulation based on sensed arm currents is adopted, these current controls can be directly implemented in local controllers without any modification since they share the same current references, controller parameters, and current feedbacks. The submodule capacitor voltage control and PWM generation are distributed into local controllers. Unlike the capacitor voltage control and balance strategies adopted in conventional MMC control systems, a capacitor voltage scheme that employs a PI controller and only relies on the capacitor voltage in the corresponding sub-module is proposed. The communication stress is eased because of the reduced information exchanging. The effectiveness of the proposed MMC distributed control architecture and capacitor voltage control scheme are confirmed by experimental results.