Earlier studies have reported some calculation methods for commutation failure fault level (CFFL) in line-commutated-converter based high-voltage direct current (LCC-HVDC) system under single-line-to-ground (SLG) faults. The accuracy of earlier methods is limited because they only consider the commutating voltage drop and phase shift, while neglecting the DC current variation. Hence, this paper proposes a CFFL calculation method under SLG faults considering DC current variation, for better planning and designing of LCC-HVDC systems. First, the fault commutating voltage magnitude and phase shift are calculated. Then, the fault DC voltage during different commutation processes is deduced. Based on the commutating voltage magnitude and phase shift, and DC voltage during different commutation processes under SLG faults, the characteristics of CFFL with different fault time are demonstrated and analyzed. Next, the transient time-domain response of the DC current after the fault is obtained based on the DC transmission line model. Discrete commutation processes are constructed based on the commutation voltage-time area rule to solve the extinction angle under different fault levels and fault time. Finally, the CFFL is calculated considering the fault time, commutating voltage drop, phase shift, and DC current variation. The accuracy of the proposed method compared with the traditional method is validated based on the CIGRE benchmark model in PSCAD/EMTDC.

中文翻译：

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考虑直流电流变化的LCC-HVDC系统单线接地故障换相失败故障等级计算方法

早期研究报道了基于线路换相换流器的高压直流（LCC-HVDC）系统在单线接地（SLG）故障下换相失败故障水平（CFFL）的一些计算方法。早期方法的精度受到限制，因为它们只考虑换流压降和相移，而忽略了直流电流的变化。因此，本文提出一种考虑直流电流变化的SLG故障下的CFFL计算方法，以更好地规划和设计LCC-HVDC系统。首先，计算故障换相电压幅值和相移。然后推导出不同换相过程中的故障直流电压。基于SLG故障下换相电压幅值和相移以及不同换相过程中的直流电压，对CFFL在不同故障时间下的特性进行了论证和分析。接下来，基于直流输电线路模型，得到故障后直流电流的暂态时域响应。基于换相电压-时间面积法则构建离散换相过程，求解不同故障等级和故障时间下的熄火角。最后，考虑故障时间、换相电压降、相移和直流电流变化来计算 CFFL。基于PSCAD/EMTDC中的CIGRE基准模型验证了所提方法与传统方法相比的准确性。