Analysis of modular multilevel converters with DC short circuit fault blocking capability in bipolar HVDC transmission systems

摘要

This paper analyzes the station-internal phase-to-ground fault in bipolar HVDC transmission systems. An overvoltage problem due to the existence of the bipolar cells in the modular multilevel converter (MMC) arms closer to the grounding pole are presented. Consequently, a new hybrid arm MMC is proposed to overcome the overvoltage problem while providing the benefits of: a lower number of cells, fewer switching devices and lower conduction losses. Guidelines are developed and confirmed by simulation results to determine the required number of cells to block the DC side fault.