Research On Detection Algorithm Of Interharmonics In Power System

With the large-scale application of power electronic devices and their control technologies to new energy generation and load control,a large number of interharmonics are injected into the power grid.The resulting power quality events and their potential risks have gradually attracted widespread attention in the power industry.Accurate detection of inter-harmonic parameters is of great significance in studying the mechanism of inter-harmonic generation,the safe operation of the power grid,and improving the efficiency of electric energy utilization.This paper first introduces the Fourier transform theory and the method of detecting interharmonics in the IEC 61000-4-7,and analyzes the problems existing in this method,and then proposes improved methods for various problems.Spectrum leakage and fence effect are two prominent problems when IEC method detects interharmonics.First of all,for the problem of spectrum leakage,a new second-order six-term Maximum Side Lobe Decay Speed(MSLD)convolution window is derived through convolution operations based on the existing six-term MSLD window,and parameters of its performance indicators are given,which greatly improves the ability to limit energy leakage.Secondly,in view of the fence effect problem,based on a new type of convolution window,a multi-spectral line interpolation algorithm is proposed,and the frequency,amplitude,and phase correction formulas are derived.Finally,the accuracy and practicability of the proposed method are verified through the analysis of Matlab simulation data and wind farm measured data.In addition,the IEC method is difficult to accurately detect interharmonics in adj acent frequency and non-stationary signals.For the above two types of signals,firstly,the matrix pencil algorithm is used to detect the steady-state signal with adjacent interharmonics in the noise situation.Secondly,for the interharmonics in the non-stationary signal,the singular value decomposition(SVD)and matrix beam algorithm combined detection method is proposed,which uses SVD to accurately locate the moment when the signal is abrupt,decomposes the non-stationary signal into multi-segment stationary signals and then uses the matrix pencil algorithm to calculate the modal parameters.The accuracy of the above method is verified by the detection of Matlab simulation data and the sub-synchronous oscillation simulation signal of the fan.The method is utilized to detect the harmonics and interharmonics in the stator current when the output power of a wind farm double-fed fan is changed.The results are consistent with the theoretical analysis and the methods have strong practicability.