Active Fault-Clearing on Long-Distance Overhead Lines using a Hybrid Modular Multilevel Converter

• Main Authors: Song, Qiang, Xu, Shukai, Zhou, Yuebin, Gim, Yunbeom, Li, Zhengxuan, Deng, Zexi
• Format: Conference Proceeding
• Language: English
• Subjects: Capacitors; Circuit faults; DC fault clearing; DC short-circuit fault; Fault currents; hybrid modular multilevel converter; Hybrid power systems; Modular multilevel converters; Resistance; Voltage control; voltage sourced converter-based high-voltage DC (VSC-HVDC)
• ISSN: 2163-5145
• DOI: 10.1109/ISIE.2019.8781312

Hybrid modular multilevel converters (MMCs) that consist of a combination of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) can block dc fault currents. Because the excessive energy stored in the dc lines must be absorbed by the capacitors of FBSMs, the FBSM overvoltage may exceed the acceptable level in the case of long-distance lines when the converter blocking approach is used. An active clearing approach is studied to clear fault current by adjusting the dc-link voltage using the negative voltage states of FBSMs. Thereby, the excess energy stored in the lines can be transmitted into the ac grid instead of being absorbed by FBSM capacitors because the hybrid MMC continuously operates during the fault-clearing process. A model for estimating the fault-clearing time of the active clearing process is proposed. Considering the expected fault-clearing time, the required number of FBSMs in the active clearing approach is analyzed. The analytical analysis method and the proposed fault-clearing strategy are verified by the simulation results.