Pole-to-ground (PTG) fault analysis is of vital importance for high-voltage direct current (HVDC) grid. However, many factors are not considered in the existing studies such as the asymmetrical property of PTG fault, the coupling issue between DC transmission lines and the complexity of the structure of DC grid. This paper presents a PTG fault analysis method, which is based on common- and differential-mode (CDM) transformation. Similar to the symmetrical component method in AC system, the transformation decomposes the HVDC grid into CDM networks, which is balanced and decoupled. Then, a transfer impedance is defined and calculated based on the impedance matrices of the CDM networks. With the transfer impedance, analytical expressions of fault characteristics that vary with space and time are obtained. The proposed PTG fault analysis method is applicable to arbitrary HVDC grid topologies, and provides a new perspective to understand the fault mechanism. Moreover, the analytical expressions offer theoretical guidance for PTG fault protection. The validity of the proposed PTG fault analysis method is verified in comparison with the simulation results in PSCAD/EMTDC.

中文翻译：

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基于共模和差模变换的高压直流输电系统地对地故障分析

接地故障（PTG）故障分析对于高压直流（HVDC）电网至关重要。然而，现有研究没有考虑许多因素，例如PTG故障的不对称性，直流输电线路之间的耦合问题以及直流电网结构的复杂性。本文提出了一种基于共模和差模（CDM）转换的PTG故障分析方法。类似于交流系统中的对称分量法，该变换将HVDC电网分解为CDM网络，该网络经过平衡和解耦。然后，基于CDM网络的阻抗矩阵定义和计算传输阻抗。利用转移阻抗，可以获得随时间和空间变化的故障特征的解析表达式。所提出的PTG故障分析方法适用于任意HVDC电网拓扑，为理解故障机理提供了新的视角。此外，解析表达式为PTG故障保护提供了理论指导。与PSCAD / EMTDC中的仿真结果进行比较，验证了所提出的PTG故障分析方法的有效性。