Modular multilevel converter based high voltage direct current (MMC-HVDC) technology has been the preferred choice for integration of renewable energy due to its advantages in power control and transmission loss etc. This paper focused on single-line-to-ground (SLG) and three phases to ground fault at valve bottom of MMC station. Theoretical analysis of variation of AC voltage and current of MMC-HVDC, DC voltage and current, and neutral to ground current of transformer after fault occurred were conducted. Characteristics of MMC-HVDC system with fault at bottom of the valve were summarized. The theoretical analysis was verified by simulation examples. The work in this paper laid foundation for configuration of converter protection in MMC-HVDC project, thus had important engineering significance in renewable energy integration process.
Keywords Flexible DC transmission, modular multilevel converter (MMC), valve bottom fault, fault characteristic analysis