Research On Analysis Methods Of Marmonics In Power System

Due to the wide application of large scale nonlinear components and the power system,a large number of harmonics are injected into the power grid,which seriously affects the power quality of the power system.But whether it is the responsibility of harmonic or harmonic control,are dependent on the characteristics of harmonic.Fast Fourier transform(FFT)is a common method for harmonic analysis.But 50 Hz is not accurate harmonic of the power system,and the existence of a large number of inter harmonics,resulting in non synchronous sampling signal,and the barrier effect,aliasing and truncation effect,lead to accurate estimation of amplitude,frequency and phase of signals.On the other hand,each peak of FFT is inevitably affected by the leakage,so it is also a key problem to give the confidence of each peak.Considering the harmonic is time-varying or transient signal,can not be a longer period of sampling,so the direct use of FFT,resulting in low frequency resolution signal analysis.Aiming at these three problems,this article studied how to improve effectively the accuracy and reliability of the estimation with low computation burden.(1)The properties of Peaks' confidence was explored preliminarily.The defect of traditional approach to judge Peaks' confidence was elaborated.By comparing the 15 quotients,got from a family of deviation,with 1,a quantitative description of Peaks' confidence can be given;(2)A new accurate estimation method of electric power harmonic parameters based on State Space Method is presented in this paper.Firstly,State Space Models is given.The parameter estimation for the robustness to noise can be transferred to seek a unitary matrix,whose eigenvalues were just the estimation of the harmonic frequency.Then the amplitude and the phase can be obtained by the least squares method or other optimization methods.Furthermore the relationship between State Space Method and Prony is researched as well as the method to select effective singular value;(3)A new accurate estimation method is presented based on FFT and State-space Model Of complex harmonic parameters in this paper.The spectral components,separated by means of Peaks' confidence,can be analyzed by Energy centrobaric,followed by State Space Method to estimate the remaining harmonic parameters.Two dimensionality reduction techniques to improve the effectiveness of the algorithm are also proposed.