基于EMD与Spearman相关系数的混合直流线路纵联保护方法

混合直流输电系统兼备常规直流以及柔性直流的优势,是直流系统发展的必然趋势。现有直流差动保护易受线路分布电容的影响,纵联保护依赖于边界条件,在混合直流输电系统中适用性差。针对以上问题,提出了一种基于经验模态分解(EMD)与斯皮尔曼(Spearman)相关系数的混合直流线路纵联保护方法。在分析故障电流增量的极性特征、考虑分布电容影响的基础上,首先对线路两端故障电流信号进行镜像延拓,通过EMD提取表征电流变化方向的残余函数,再计算残余函数的Spearman相关系数,以此识别线路内外部故障。该方法不受分布电容影响、不依赖于边界条件。通过仿真验证,所提保护方案动作速度快、可靠性高,且具有较强耐受过渡电阻与抗噪声干扰的能力。

Hybrid HVDC line pilot protection method based on EMD and Spearman correlation coefficient

A hybrid HVDC transmission system combines the advantages of LCC-HVDC and MMC-HVDC, and their adoption is an inevitable trend in the development of HVDC systems. Existing DC differential protection is susceptible to the influence of line distributed capacitance, and pilot protection depends on the boundary conditions. This has poor applicability in hybrid HVDC transmission systems. In response to the above problems, a hybrid HVDC line pilot protection method based on Empirical Mode Decomposition (EMD) and Spearman correlation coefficient is proposed. To analyze the polarity characteristics of the fault current increment and considering the effect of distributed capacitance, first, the fault current signals at both ends of the line are mirror-extended, and the residual function representing the direction of current change is extracted by EMD. Then the Spearman correlation coefficients of residual functions are calculated to identify the internal and external faults of the line. This method is not affected by distributed capacitance and does not depend on boundary conditions. Simulation results show that the proposed protection has fast operation, high reliability, and a strong ability to withstand transition resistance and noise interference. This work is supported by the National Natural Science Foundation of China-State Grid Joint Fund for Smart Grid (No. U2066210).