On-line Monitoring Method of Submodule in MMC Based on Kalman Filter Algorithm

In flexible high voltage direct current (HVDC) system, aging and failure of the submodule components in modular multilevel converter (MMC) threatens the safe and stable operation of the system. In this paper, a method on monitoring parameters of capacitors, IGBTs and diodes in submodule (SM) simultaneously is proposed, which presents the state of SMs. According to the relationship between the state of switching devices and the voltage of capacitor in SMs, a mathematical model of bridge arm voltage in MMC is established. Then, Kalman filter is introduced to monitor the parameters of elements, which can prevent the influence of sensor measurement noise and save storage space. Next, the state of the submodule capacitor, IGBTs and the diodes is monitored through the established mathematical model and repeating the Kalman filter algorithm multiple times. Finally, the scheme is verified by building an MMC-HVDC transmission system in Power Systems Computer Aided Design (PSCAD) simulation platform. The result shows that the estimation error is less than 1%, which is satisfied to the on-line monitoring in practical engineering and can improve the reliability of the system.