中文摘要：

介绍了一种新的非线性、非平稳信号分析方法——局部均值分解（local mean decomposition，LMD），分析了LMD用于扰动信号检测时的优缺点及原因。在此基础上，提出一种改进的局部均值分解（improved local mean decomposition，ILMD）电能质量扰动检测及时频分析新方法，该方法由LMD和希尔伯特变换（Hilbert Transform，HT）2部分组成。先用LMD提取信号的乘积函数（product function，PF），由PF分量的调幅函数可得信号瞬时幅值；再对PF分量进行HT求取瞬时频率。ILMD方法可有效定位发生扰动的起止时刻，克服LMD在定位能力上的不足。与采用希尔伯特黄变换（Hilbert Huang transform，HHT）方法相比，ILMD具有瞬时幅值函数端部失真小、瞬时幅频曲线波动小和幅值与频率检测精度高等优点。仿真信号和500kV变电站电容器组投切时的电压信号分析结果证明所提方法的可行性和有效性。

英文摘要：

A new signal analysis method of non-linear, non-stationary--local mean decomposition （LMD） was introduced. The advantages and disadvantages of the application of LMD in the disturbance signal detection were analyzed. On this basis, the paper presented an improved local mean decomposition （ILMD） power quality disturbance detection and time-frequency analysis method. The method was composed of two parts： LMD and Hilbert transform. Firstly, to extract the product function （PF） of the signal based on LMD, and to obtain the instantaneous amplitude of the signal from the PF components of the amplitude modulation function. Then, to apply the Hilbert transform to obtain the instantaneous frequency of PF. The improved LMD method could effectively locate the beginning and ending time of the disturbances occurred and overcome the deficiencies of the LMD positioning capability. By using the method, the curves of the instantaneous amplitude had less distortion in wave head and that of the instantaneous frequency had shorter swings, and detection results for magnitude and frequency of disturbance signal had higher accuracy, compared with the HHT method. The simulation and experimental results of the switch voltage analysis of capacitor group from 500 kV transformer substation prove the feasibility and effectiveness of the proposed method.