Abstract The pole-to-ground fault is the most common fault in the true bipolar modular multilevel converter based high voltage direct current (MMC HVDC) grid. The study of a fault current calculation method and characteristics is the theoretical basis for relay protection and fast fault isolation technology of MMC HVDC grid. Considering the mutual inductance coupling between lines, this paper proposes a general fault current calculation method for pole-to-ground faults in MMC HVDC grids. Firstly, considering the influence of AC system on MMC and the mutual inductance coupling between lines, the complex frequency domain equivalent model of the MMC HVDC grid and the simplified model of the remote converter station are studied. Based on the characteristics of the true bipolar MMC HVDC grids, the circuit is analyzed in the complex frequency domain, and an improved node voltage method combined with voltage current relation (VCR) is proposed to calculate the MMC HVDC fault current and obtain the corresponding expression. Finally, the proposed method is validated by comparing its calculation results with the simulation results performed on PSCAD/EMTDC, and the characteristics of the pole-to-ground fault in the MMC HVDC grid are further summarized.

中文翻译：

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考虑线路耦合的真双极MMC-HVDC电网极地故障电流计算方法及特性研究✰

摘要 在基于双极模块化多电平换流器的高压直流（MMC HVDC）电网中，极地故障是最常见的故障。故障电流计算方法和特性的研究是MMC直流电网继电保护和快速故障隔离技术的理论基础。考虑到线路间的互感耦合，本文提出了一种通用的MMC HVDC电网极地故障的故障电流计算方法。首先，考虑交流系统对MMC和线路间互感耦合的影响，研究MMC HVDC电网的复频域等效模型和远程换流站的简化模型。基于真双极MMC HVDC电网的特点，在复频域对电路进行分析，提出了一种结合电压电流关系(VCR)的改进节点电压法计算MMC HVDC故障电流并得到相应的表达式。最后，通过将其计算结果与PSCAD/EMTDC上的仿真结果进行比较验证了所提出的方法，并进一步总结了MMC HVDC电网中极地故障的特征。