Analytical Modelling and Resilient Operation Design for Capacitor Voltage Ascent in MMC Distributed Control System with Communication Interruption

Modular Multilevel Converters (MMCs) in HVDC applications usually adopt a distributed control architecture to manage enormous sub-modules (SMs) through a communication network. The communication congestion and network disconnection befell during the data exchange lead to communication interruption (CI) and eventually cause the system malfunction. An analysis of the influence of CI to the MMC system output current and the SM capacitor voltage is presented. A resilient operation strategy is proposed which ensures the MMC system stable operation during CI fault. The analysis indicates that the insertion index of the fault SM becomes constant with the presence of CI. The constant insertion index, in some way, distorts the output current and makes the fault SM operating in a critical condition. The proposed resilient operation method retrieves the SM power balance by utilizing pre-stored phase signals to generate the sinusoidal insertion index. Good agreement of the capacitor voltage deviation after CI has been achieved between the theoretical and experimental results. The proposed resilient operation method is verified that it significantly reduces the impacts introduced by CI.