Research On Complex Harmonics/Inter-harmonics With Spectrum Interference Using Time-frequency Mixing Algorithm

With the new energy power generation and electronics technology widely used in the power system,Harmonics components in the power grid are becoming more and more complex.Comparing with the traditional integer harmonics,inter-harmonics frequency is uncertain.Thus,when the harmonic frequency is adjacent to the fundamental,harmonic or other interharmonics,which spectrum will spread to the nearby line to produce the main-lobe interference.In addition,when the signal is Fourier transformed,a positive and negative bilateral spectrum is obtained,However,spectral analysis generally only takes into account the positive frequency components,and the negative frequency component causes negative frequency interference when the harmonics/inter-harmonics frequency is very low or very high to near the Nyquist sampling frequency.At this time,its conventional harmonic/inter-harmonics analysis method can not parse correctly.A Time-frequency Mixing Algorithm is proposed to rapidly detect and analyze the harmonics/inter-harmonics signal that contains main-lobe interference and negative frequency interference in the modern power grid.Firstly,the FFT spectrum estimation is utilized to the analyzed signal with Hanning Self-Convolution Windows functions,based on the phase characteristic and the amplitude ratio correction theory of the frequency domain spectral,a synthesized and high credibility spectrum interference criterion is proposed to determine whether spectrum interference occurs in the frequency domain.When the spectrum interference is detected from the harmonic/inter-harmonic spectrum lines,the PSO algorithm is used to search the approximate range of parameters in adjacent of spectrum lines,then the rough parameters are discretized and the atomic decomposition algorithm is applied to search the best matching atom in a smaller range to obtain the precise parameters of harmonic/inter-harmonic signals.If the spectrum interference dose not exist,Hanning Self-Convolution Windowed frequency shifting algorithm is employed to adjust the maximal magnitude component frequency to remove and get the parameters of harmonics/inter-harmonics.This algorithm not only avoids the problem that the frequency shift algorithm can not interfere with the harmonics/interharmonics detection of spectrum interference,but also iterations and computation are reduced,and the searching result is guaranteed to be global optimal solution.The simulation results demonstrate that the proposed method can rapidly and effectively detect the harmonic/inter-harmonic signal that contains spectrum interference.Finally,In the Matlab simulation platform,the frequency shifting algorithm,the atomic decomposition algorithm and the hybrid algorithm are used to compare the results of complex harmonic and interharmonic parameters.Then,the complex signals with spectral interference are simulated in the Gaussian white noise environment analysis,The simulation results show that the proposed hybrid algorithm is effective and has some anti–noise.