Research On High Precision Harmonic Parameter Estimation Method Based On Fast Fourier Transform

In modern power systems,due to the presence of a large number of non-linear components in the power grid,resulting in the generation of harmonics and inter-harmonics,the safe operation of the power grid itself is seriously threatened.Therefore,accurate estimation of harmonic parameters plays an important role in the monitoring and protection of power systems.The methods of harmonic estimation based on fast Fourier transform(FFT)are widely used because of their simple principles,high accuracy of parameter estimation,and ease of implementation.However,when using FFT to process the signal,due to the influence of factors such as asynchronous sampling and non-integer period truncation,the phenomenon of fence effect and spectrum leakage phenomenon occur,resulting in the signal parameter cannot be accurately estimated,so how to accurately estimate the information of frequency,amplitude and phase of the harmonic have aroused extensive attention of researchers.In view of the above,this paper focuses on the analysis of the principle of FFT,the spectral characteristics of the window function,and the attenuation characteristics of the frequency-domain sequence after FFT processing,which provides a solid foundation for designing new high-precision algorithms for harmonic parameter estimation.The research work of this paper mainly included the following three aspects:(1)The background of harmonic research,the significance of harmonic research and its current status at home and abroad are introduced.The harmonics of definition,harm,and cause are briefly explained,the principles of common harmonic parameter estimation methods and their advantages and disadvantages are compared,and the fast Fourier transform is selected as the research method of harmonic detection in this paper.This article focuses on the extent to which the different windowing and interpolation methods proposed by scholars at home and abroad have a negative impact on reducing spectral leakage and barrier effects,as well as their improvement in the accuracy of signal parameter estimation.(2)By comparing the spectral characteristics of the conventional window function,the estimation accuracy and complexity between the interpolation of different spectral lines,a method of triple-spectrum-line interpolation based on the Blackman-Harris self-multiplication window is proposed.From the analysis of the spectrum characteristics,the Blackman-Harris self-multiplication window greatly suppresses the spectrum leakage.The signal parameter estimation formula is derived based on the combination of the method of Blackman-Harris self-multiplication window and the triple-spectrum-line interpolation.The polynomial curve fitting method is used to obtain the estimated expressions of the frequency,amplitude and phase parameters of harmonic of the second-order Blackman-Harris self-multiplication window(BHSM-2)and third-order Blackman-Harris self-multiplication window(BHSM-3).The simulation results show that both BHSM-2 and BHSM-3 can effectively improve the parameter estimation accuracy of harmonics and inter-harmonics,and have higher accuracy than the traditional of window function parameter estimation.When the fundamental frequency changes,both BHSM-2 and BHSM-3 can maintain high accuracy in harmonic parameter estimation.(3)Based on the analysis of spectral line attenuation characteristics,a high-precision harmonic analysis algorithm based on spectral sequence transformation is proposed.The new algorithm performs a specific weighted transformation on the spectral sequence obtained via FFT,which accelerates the attenuation rate of spectral lines at the unreal frequencies,and thus effectively suppresses the spectrum leakage.Based on this,an effective estimation method of harmonic amplitude and phase is proposed.The simulation results show that,compared with the classical windowed interpolation algorithm and other improved FFT algorithms,the new algorithm improves the accuracy of parameter estimation significantly,and shows excellent performance when the fundamental frequency changes or inter-harmonics exist.In addition,compared with the classical windowed interpolation algorithms,the new algorithm only needs simple processing of spectral sequence,and has the advantage of low computational complexity.