This paper investigates the in-depth mechanism of commutation failure for a line-commuted converter-based high-voltage direct current (LCC-HVDC) system. The commutation failure prevention control (CFPREV) and the initial fault voltage angle (IFVA) are considered from the view of the voltage-time area (VTA) in the analysis. It is revealed that the IFVA is among the dominant factors for commutation failures when the voltage drop of the inverter bus is relatively small, and CFPREV further intensifies the impact of the IFVA on commutation failures, while the fluctuation of the direct current plays a dominant role in commutation failures under a greater voltage reduction at the inverter bus. A quantitative division of the severity of AC faults is proposed to determine dominant factors for commutation failures. The relationship between the chance of commutation failures to occur and the IFVA is built, and the method used for computing probability of commutation failures is proposed. The influence of the dynamic of CFPREV output on our research is studied. Simulations based on a typical monopole LCC-HVDC system using PSCAD/EMTDC software are conducted to verify the correctness of the theoretic analysis and the effectiveness of the proposed computing methods.

中文翻译：

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考虑CFPREV和初始故障电压角的LCC-HVDC系统换相失败概率分析

本文研究了基于线路换流器的高压直流 (LCC-HVDC) 系统的换相失败的深入机制。分析中从电压-时间区(VTA)的角度考虑换相故障预防控制(CFPREV)和初始故障电压角(IFVA)。结果表明，当逆变母线压降较小时，IFVA是换相失败的主导因素，CFPREV进一步加剧了IFVA对换流失败的影响，而直流波动起主导作用在逆变器总线上更大的电压降低下的换向故障中。提出了交流故障严重程度的定量划分，以确定换相故障的主要因素。建立了换相失败概率与IFVA的关系，提出了换相失败概率的计算方法。研究了 CFPREV 输出的动态对我们研究的影响。使用PSCAD/EMTDC软件基于典型的单极LCC-HVDC系统进行仿真，以验证理论分析的正确性和所提出的计算方法的有效性。