Reliability and Sensitivity Model for Bipolar MMC-HVDC Including States of Sub-modules

The modular multilevel converter (MMC) based high voltage dc (HVDC) is flexible for control. Its reliability analysis is of important application value. The state space model of the bipolar MMC-HVDC including the sub modules (SMs) is proposed in this paper. The equivalent outage hours (EOH) and the bipolar availability (BA) are calculated. The availability of MMC (AMMC) and reduction rate of EOH (αEoH) are newly defined in this paper. The analytical expression of the sensitivity of reliability indices with respect to the redundancy number is newly derived. The numerical analysis compares the reliabilities of the MMC-HVDC and the VSC-HVDC. The MMC-HVDC with different numbers of redundant SMs is evaluated to verify the necessity of considering the availability of the SMs.