With the rapid development of renewable energy, multi-terminal flexible DC grids composed of modular multilevel converters have been widely used in power systems. To ensure the safe and stable operation of a DC grid, this paper proposes a DC line protection scheme for MMC-based DC grids using AC/DC transient information. In the proposed scheme, the difference between the transient voltage root mean square ratios (DTVR) on both sides of the current-limiting inductor of DC lines is used to identify the DC line fault, and the instantaneous zero sequence voltage (IZSV) of the AC side of the converter station is used to discriminate the faulted poles. According to the theoretical analysis result, a fault criterion setting method suitable for faulted pole discrimination is proposed. The proposed scheme is based on local information and tested in a PSCAD/EMTDC model of a four-terminal MMC-based DC grid. The simulation results show that the scheme can fast and accurately identify faults.

中文翻译：

---

基于交流/直流瞬态信息的基于MMC的直流电网的直流线路保护方案

随着可再生能源的快速发展，由模块化多电平换流器组成的多端柔性直流电网在电力系统中得到广泛应用。为确保直流电网的安全稳定运行，本文提出了一种基于交直流瞬态信息的基于MMC的直流电网的直流线路保护方案。该方案利用直流线路限流电感两侧暂态电压均方根比（DTVR）的差值来识别直流线路故障，利用直流线路的瞬时零序电压（IZSV）换流站交流侧用于判别故障极。根据理论分析结果，提出了一种适用于故障极判别的故障判据设置方法。所提出的方案基于本地信息，并在基于四端 MMC 的直流电网的 PSCAD/EMTDC 模型中进行了测试。仿真结果表明，该方案能够快速准确地识别故障。