Design of Sub-synchronous Oscillation Damping Controller in MMC-MTDC for SSO Suppression

Aiming on the sub-synchronous oscillation (SSO) of hybrid AC-DC system which contains modular multilevel converter based multi-terminal direct current (MMC-MTDC) transmission, a novel sub-synchronous oscillation damping controller (SSDC) which suits the system's multiple operational modes and has better universality was designed. Firstly, the system's operational mode and MMC's control mode were analyzed for the hybrid system. Focusing on their effects on restraining SSO, a SSDC designing method suiting the changes of MMC's control mode was proposed. Then, the new SSDC's effect on improving system's electrical damping was analyzed. Finally, the simulation model was built on PSCAD/EMTDC, and the results validated the correctness of the designing method and the effectiveness of the new SSDC. It was found that the SSDC designed by this new method has a better universality and it can strengthen the system's electrical damping observably as well as decrease the risk of SSO efficiently in all operational modes.