The Research And Applicationon Of Inter-harmonic Detection Methods In Power System

With a large number of non-linear equipment such as power electronics applied to the grid,the content of harmonics and interharmonics caused by it keeps increasing.As a special form of harmonics,interharmonics sets non-linearity,randomness,non-stationarity etc.features together.So the harm caused by interharmonics are far more than harmonics;And interharmonics can also have a disturbing effect on power system,such as voltage fluctuations and flickers etc.This series of disturbances not only threaten the security of the power system but also affect the power quality in daily life.Therefore,it is very important and practical to improve the detection algorithm of interharmonics and study the influence of interharmonics on power system disturbance.The main content in this paper are as follows:(4)To improve the detection accuracy of interharmonics in power system,this paper improved a HHT(Hilbert-Huang Transform)algorithm.The algorithm involves classical EMD(Empirical Mode Decomposition),EEMD(Ensemble Empirical Mode Decomposition),Multi-resolution analysis and Hilbert transform.When applying EMD,the classical HHT algorithm has modal aliasing problem,which lead to poor detection accuracy.However,the improved algorithm combines the advantages of EEMD,multi-resolution analysis and Hilbert transform.By simulating the improved algorithm and the classical algorithm with different signal models in the literature,and comparing the simulation results,it can prove that the improved HHT algorithm can effectively detect interharmonic signals and has high accuracy,however the detection accuracy of the paper cannot be effectively improved for interharmonics with similar frequencies.(5)Due to the presence of near-frequency interharmonics in actual power system,the classical algorithms cannot accurately detect interharmonics.The paper improved a MUSIC detection algorithm by fully analysising the advantages and existing problems of EEMD transform and MUSIC algorithm.The improved method involes EEMD,energy threshold method,MUSIC and least square method.Simulate the improved algorithm with signal model,and compare the simulation results with the test results of classical algorithm and literature.The comparison shows that: The improved algorithm can effectively detect the near-frequency harmonics,and has high detection accuracy.(6)Because it is difficult to accurately detect and locate voltage fluctuations and flicker disturbances caused by interharmonics influence,so this paper studies a disturbance and location algorithm of voltage fluctuation and flicker based on CEEMD(Complete Ensemble Empirical Mode Decomposition)and mathematical morphology.This paper uses two groups of simulation signals,Single interharmonic disturbance model and Compound interharmonics disturbance model,to test the improved algorithm and compare the simulation results with the literature.The results show: The improved algorithm has high accuracy and effectiveness for voltage fluctuation and flicker disturbance detection caused by interharmonics.It can also accurately locate the position of the flicker in the power system signal.