Capacitor Voltage Round-robin Transmission Modes with Voltage-Ripple-Filtering Capability for an MMC Distributed Control System

In most MMC distributed control structures, the sub-module capacitor voltages measured in local controllers have to be transmitted to the central controller, through a communication network, in order to perform the phase average capacitor voltage control. The known transmission mode is to deliver all SM capacitor voltages within one control cycle. It causes heavy communication burden to an MMC with numerous SMs. Two capacitor voltage round-robin transmission modes with voltage-ripple-filtering capability are proposed in this paper to reduce the communication burden while eliminating the filters in voltage control loops. Moreover, the filtering effects of the two proposed transmission modes are studied to filter out specific harmonics with minimum data transmission by selecting different transmission intervals. Finally, the feasibility of the two proposed transmission modes is confirmed by experimental results.