Research On Detection Algorithm Of Power Grid Harmonics,Interharmonics And Supraharmonics

With the continuous increase of non-linear loads in the power system and the rapid development of power electronics technology,a large number of harmonics,interharmonics and supraharmonics are injected into the power grid,resulting in a serious deterioration of the power quality of the power grid.Accurate detection of harmonics,interharmonics and supraharmonics is the premise of its treatment,which is of great significance to maintain the safe and stable operation of power system.Fast Fourier Transform(FFT)algorithm is the main tool of harmonic analysis,but it will produce spectrum leakage and fence effect when non-synchronous sampling or non-integral period truncation,which will affect the detection accuracy of harmonics and interharmonics.To solve this problem,the characteristics of common window function and the selection principle of window function are discussed,and the time-domain window is used to suppress the spectrum leakage.The correction process of bispectral interpolation algorithm is derived,and the frequency domain interpolation is used to reduce the fence effect.At the same time,the correction formulas of related parameters under different window functions and the frame of windowed interpolation FFT algorithm are given.The simulation results show that the improved algorithm can effectively suppress spectrum leakage and fence effect compared with the traditional FFT algorithm,and improve the detection accuracy of harmonics and interharmonics to a certain extent.Then,based on the windowed interpolated FFT algorithm,combined with the all－phase FFT data preprocessing process and the principle of spectrum analysis,a harmonic and interharmonic detection algorithm based on double-window all-phase FFT bispectral line interpolation is proposed.This paper estimates the initial phase of a signal by using the phase values of the main spectral line of double-window all-phase FFT,and selects the left and right spectral lines immediately adjacent to the peak frequency point to correct the frequency and amplitude.At the same time,a practical correction formula under the typical window function of all-phase FFT is derived by combining the polynomial fitting function.Compared with the traditional FFT double-spectral-line interpolation method,all-phase FFT ratio method,and all-phase FFT phase difference method,the accuracy and effectiveness of the novel algorithm are verified in terms of dense spectrum analysis,high-precision detection of harmonics and interharmonics,and overcoming the white noise pollution.In order to alleviate the problem of massive data sampling and transmission in supraharmonic detection under Nyquist sampling theorem,the compressed sensing theory is applied to the detection of supraharmonic signals in power grid,and a compressed sensing supraharmonic detection algorithm based on winded measurement matrix and interpolation correction is proposed.Analyze the sparsity of supraharmonic signals under the DFT basis to meet the prerequisites of compressed sensing,construct a windowed measurement matrix to compress and sample the original signal to essentially suppress spectrum leakage,adopt sparsity adaptive compressed sampling matching tracking algorithm to realize ultra-high harmonic compression and reconstruction,and perform interpolation correction on the reconstructed sparse signal to reduce the detection error.Finally,the simulation results show that the proposed algorithm has certain advantages in detection accuracy,compression performance and anti-noise ability,which can break through the limitations of Nyquist sampling theorem on sampling frequency,and realize the accurate detection of supraharmonic components with less data.