Reliability Evaluation of MMC‐MTDC System Considering Device Failure Rates and Multi‐State Transition

ABSTRACT The modular multi‐level converter based multi‐terminal high voltage direct current (MMC‐MTDC) system, with its numerous power devices and diverse operating states, poses a significant challenge for reliability evaluation. The paper introduces a method for modeling and assessing the reliability of MMC‐MTDC, considering both power device failure rates and multi‐state transitions of multiple terminals. To determine the weights of influence, the analytic hierarchy process (AHP) is employed to evaluate the impact of sub‐modules (SMs), the controller system, and the water cooling systems of an MMC. Subsequently, a multi‐state transition model is established to describe the changes in the operation mode of the MMC‐MTDC. On this basis, the reliability evaluation via semi‐Markov processes is implemented. A case study is performed on the reliability of a ±200 kV five‐terminal system and the results are compared with practical operation data.