| Traveling wave protection has the characteristics of fast response speed,high accuracy and no system oscillation,and has become an important development direction of transmission line protection.However,when the traveling wave sensor transmits the traveling wave signal,the signal attenuates,and it is difficult to accurately identify the fault feature information contained in the traveling wave signal,which makes the reliability of traveling wave protection low and difficult to meet the application requirements of power system.In order to improve the detection accuracy of traveling wave signals,an accurate detection method of voltage traveling wave based on frequency division inversion is proposed.Firstly,this thesis analyzes the methods of signal detection in the power system,and summarizes the problems existing in detecting traveling wave signals by various methods.Then,the traveling wave sensor is studied,and the signal transmission characteristics in different frequency bands are analyzed.The waveform inversion model of the sensor is established,and the inversion model is solved by using the conjugate gradient inversion method.The simulation found that it is easy to fall into the local extremum when directly solving inversion,and the inversion effect is not good.In order to further improve the accuracy of the inversion,the paper considers the inversion of the signal by frequency band.This paper studies three frequency division algorithms,and makes a comparative analysis.By comparing the frequency spectrum and waveform correlation coefficients of the decomposed signal components,the variational mode decomposition algorithm is selected.The key parameters in variational mode decomposition are selected from the aspects of mode aliasing effect,frequency domain bandwidth and waveform correlation coefficient.Finally,an accurate voltage traveling wave detection method based on frequency division inversion is proposed.In this method,a simulation model is established on the PSCAD/EMTDC platform to obtain traveling wave signals under different fault conditions,and then a sensor model is established on MATLAB/Simulink platform to obtain the traveling wave signals on the secondary side of the sensor.The second signal of the sensor is decomposed into several intrinsic modal function components with different characteristic frequencies by using variational modal decomposition algorithm;Inversion signals of each component are obtained by conjugate gradient inversion,and finally the inversion signal is synthesized.Detection of traveling wave signals.The simulation results show that,under different fault conditions and signal-to-noise ratios,the detection methods proposed in this paper can realize accurate detection of traveling wave signals,and avoid positioning errors and overprotection caused by poor signal detection results of traveling wave protection technology.The problem of abnormal operation improves the practicability of traveling wave protection. |
