28. Internal AC Fault of a Converter Station Based on Modular Multilevel Converter High Voltage Direct Current

The chapter introduces the structure and operational mechanism of a modular multilevel converter based on high voltage direct current (MMC-HVDC), analyzes the internal alternating current (AC) system fault with emphasis, and puts forward the corresponding protection and control strategy. The MMC-HVDC connected to a wind farm simulation model is set up in power system computer aided design/electromagnetic transient including direct current (PSCAD/EMTDC). The simulation results show that during the interphase, the short circuit fault in the AC bus could cause serious accidents and the fault could be passed through the DC line to the nonfault converter. So it often requires to shut down the converter station—even both. However, the AC voltage on the nonfault converter would not be impacted. When troubleshooting, the system could adjust by self-tuning the control system into a stable state again.