基于SURE小波阈值消噪和MCEEMD-HHT的低频振荡分析

Analysis of Low-frequency Oscillation Based on SURE Wavelet Threshold De-noising and MCEEMD-HHT Method

为解决低频振荡分析中广域量测系统存在量测噪声影响和应用希尔伯特黄变换(Hilbert-Huang transform,HHT)进行模态辨识中的模态混叠和伪分量问题,提出基于Stein的无偏似然估计(Stein unbiased risk estimate,SURE)小波阈值消噪和改进的补充集合经验模态分解希尔伯特黄变换(modified complementary ensemble empirical mode decomposition and Hilbert-Huang transform,MCEEMD-HHT)的低频振荡分析方法。首先,对含较强噪声的电网量测低频振荡信号,采用SURE小波阈值消噪实现信号预处理。其次,引入排列熵算法改进CEEMD形成MCEEMD,有效抑制经验模态分解中的模态混叠和伪分量现象。最后,对MCEEMD分解得到的低频振荡真实模态进行HHT分析。通过复合信号测试、IEEE四机两区域系统仿真以及实测北美电网数据分析,验证了所提方法在电力系统低频振荡分析中的有效性。此外,与快速傅里叶变换(fast Fourier transform,FFT)、Prony算法分析进行对比可知,所提方法在模态参数的提取方面表现得更为准确,且无需人为定价。

To solve the problem of noise measurement in wide area measurement system,we proposed a low-frequency oscillation analysis method based on Stein unbiased risk estimate(SURE)wavelet threshold de-noising and modified complementary ensemble empirical mode decomposition and Hilbert-Huang transform(MCEEMD-HHT).Furthermore,the proposed method is used to solve the problem of mode mixing and pseudo components in mode identification using Hilbert-Huang transform(HHT)in the analysis of low-frequency oscillation.Firstly,the low-frequency oscillation signal of power network measurement with strong noise is pre-processed by using SURE wavelet threshold de-noising.Secondly,the permutation entropy algorithm is introduced to improve CEEMD to form MCEEMD,which can effectively suppress the phenomenon of modal aliasing and pseudo components in EMD.Finally,HHT analysis is carried out on the real low-frequency modes obtained by MCEEMD decomposition.Through the composite signal tests,IEEE four-generator two-area system simulation,and an actual measured North American power grid data analysis,it is shown that the proposed method is effective in the analysis of power system low-frequency oscillation.In addition,compared with fast Fourier transform(FFT)and Prony algorithm analysis,the proposed method is more accurate in the extraction of modal parameters and does not need an artificial order determination.