基于局部均值分解（LMD）的单通道触电信号盲源分离算法

针对从低压电网的剩余电流中提取触电电流的难题,该文提出局部均值分解(local mean decomposition,LMD)与盲源分离相结合提取触电电流的方法。利用LMD算法自适应的将剩余电流信号分解为若干个PF(product function)分量,计算各分量与原始信号的相似系数,选取相似系数最大且大于0.8的模态分量构造虚拟通道,与剩余电流信号一起构建盲源分离的2个通道,再利用FastICA算法从剩余电流信号中提取触电电流。试验结果表明:相较于经验模态分解(empirical mode decomposition,EMD)时间0.129 s,LMD分解时间为0.032 s,速度更快;在单相电路触电时,基于LMD-FastICA算法和EMD-FastICA算法提取的触电电流与原始触电电流的平均相关系数分别为0.937 4和0.925 3,平均相对误差分别为0.096 2和0.109 8;在三相电路触电时,基于LMD-FastICA算法和EMD-FastICA算法提取的触电电流与原始触电电流的平均相关系数分别为0.962 4和0.948 9,平均相对误差分别为0.056 4和0.081 55;LMD-FastICA与EMD-FastICA两种算法分解信号的峰值因子的相对误差范围分别为0.001～0.103和0.012～0.155,且抑制端点效应更好。研究结果可为开发基于触电电流动作的新型剩余电流保护装置奠定理论基础。

Single channel electric shock signals blind source separation algorithm based on local mean decomposition

Abstract: Residual current protection device (RCD) is a kind of protection device in low voltage system and has been widely applied in preventing of grid leakage and protecting of peoples life and property safety. At present, the action threshold of residual current protection device is 30 mA, but there is no direct relation between the action setting value and the electric shock current passing through the electric shock body. When heavy load is put into operation or weather changes or electric shock occurs, residual current protection device often occurs misoperation or rejection. Therefore, extracting electric shock current from the residual current and setting a new protection action criterion are of great significance for improving the operational reliability of residual current protection device. Because electric shock accident is unpredictable, it is difficult to extract the electric shock current from the residual current of low voltage power network exactly. A method of extracting the electric shock current by combining the local mean decomposition (LMD) with blind signal separation is proposed. In general, the observed signals used for blind source separation are multi-channel signals. When electric shock occurs, the residual current signals contain the electric shock current signals, normal leakage current signals and noise signals. The residual current signal is a single channel signal, and at least one virtual channel needs to be constructed. Therefore, using the local mean decomposition method, the residual current signal is adaptively decomposed into the sum of several product functions(PF), and each product function is equal to the product of an amplitude modulated signal and a frequency modulated signal. Computing the similarity coefficient between each component and the original signal, the modal components with the largest similarity coefficient and greater than 0.8 are used as virtual channels for blind source separation. Two channels of blind source separation are constructed by combining virtual channels with residual current signals, and the problem of single channel blind source signal separation was solved. Then FastICA algorithm was used to extracte the electric shock currents from the residual current signals. The results shown that LMD method has less decomposition component, shorter calculation time compared with empirical mode decomposition (EMD) method, and can avoid the disadvantage of endpoint effect in the decomposing process of EMD. When electric shock accident occur in single-phase circuit, the average correlation coefficients between the original electric shock current and the electric shock current extracted by LMD-FastICA and EMD-FastICA are 0.937 4 and 0.925 3 respectively, the average relative errors are 0.096 2 and 0.109 8 respectively. The relative error ranges of peak factor of decomposition signal by EMD-FastICA and LMD-FastICA is from 0.012 to 0.155 and from 0.001 to 0.103 respectively. When electric shock accident occur in three-phase circuit, the average correlation coefficients between the original electric shock current and the electric shock current extracted by LMD-FastICA and EMD-FastICA are 0.962 4 and 0.948 9 respectively, and the average relative errors are 0.056 4 and 0.081 55 respectively. The calculation time of LMD-FastICA(0.032 s) is shorter than that of EMD-FastICA(0.129 s). The research results lay a theoretical foundation for development of new residual current protection device based on the action of electric shock current.