Research On The Method For Separating Low Frequency Disturbance In PMU Data

With the continuous construction and improvement of wide-area measurement system in China,the data collected by phasor measurement units is widely used in the real time dynamic process monitoring system of power network.When low frequency oscillation occurs in the power grid,as Fast Fourier algorithm adopted by PMU can’t distinguish the power frequency signal and low frequency disturbance,the collected PMU data will include low frequency disturbance component,which affects the correctness of steady state analysis and calculation of power network.In order to extract the fundamental frequency variables in PMU data,taking the forced low frequency oscillation as an example,a method for separating low frequency interference from PMU data was proposed in this paper.Results from theoretical analysis,simulation test and actual PMU data analysis show the correctness and validity of the proposed method in this paper.The main research contents and results are as follows:(1)The paper analyzed the characteristics of disturbance variables in power system under forced low frequency oscillation.The importance of eliminating the low frequency interference in PMU data is pointed out before analyzing and calculating the steady stability of power system.(2)A method is proposed to separate the low frequency from the PMU data to obtain the fundamental frequency variable.The detailed practices are as follows: extracting the local maximum and minimum values of measured signal;fitting the maximum envelope and the minimum envelope and calculating the mean value by using piecewise three Hermite difference;extracting fundamental frequency variable that meeting the accuracy requirements.(3)The influence of low frequency disturbance on fundamental frequency active power is analyzed,by establishing three-phase voltage source model to simulate and vary.The correctness and effectiveness of the proposed method in this paper is verified by using actual PMU data.(4)Finally,the paper analyzed the impact of low frequency oscillation on SCADA data.Simulating the data characteristics in SCADA system by reducing the sampling frequency to study the error caused by low frequency disturbance during the line fundamental parameter calculation.The results of theoretical analysis,simulation test and actual PMU data analysis show that the method proposed in this paper can quickly and accurately obtain the fundamental frequency variable without low frequency interference.This method is of great significance to improve the value of PMU data and ensure the monitoring function of WAMS.