Research On Harmonic Parameter Analysis Method Based On Composite Window

With the rapid development of modern power industry and power electronics technology,a large number of nonlinear components are applied to the power system,resulting in a large number of harmonics in the power grid.Harmonics not only pose a threat to the safe operation of the power grid,but also seriously affect the quality of power.Therefore,harmonic control is necessary.Harmonic detection is the premise of harmonic control.Its main work is to detect harmonic parameters with high accuracy.Fast Fourier transform(FFT)is widely used because of its simple principle and easy implementation.However,when using FFT,there will be spectrum leakage and picket fence effect,which can affect the detection accuracy of harmonic parameters.Therefore,how to accurately and quickly detect harmonic parameters is of great significance to harmonic control and power quality improvement.This paper mainly works from the following three aspects:1.The problems of spectrum leakage and fence effect in FFT method are analyzed,and the windowed interpolation method can suppress the influence of spectrum leakage and fence effect.Some classical cosine window functions are listed,their spectrum characteristics are analyzed,and the three spectral line interpolation method is introduced.The harmonic signal detection algorithm based on classical cosine window three spectral line interpolation FFT is proposed,and simulation experiments are carried out in integer harmonic and interharmonic scenarios.The detection accuracy of harmonic parameters is higher than that of traditional FFT methods.2.To better suppress spectral leakage,an adjustable Rife-Vincent self-multiplication-convolution window(RVSMC)is proposed.The advantage is that the main-lobe width,side-lobe level and side-lobe roll-off speed of the window function can be flexibly changed by changing the multiplication or convolution order.On this basis,a high-precision harmonic parameter estimation method based on RVSMC window four-spectral-line interpolation is proposed,which uses the theory of least squares fitting to give the polynomial estimation formulas of the amplitude,frequency and phase parameters of the harmonic signal.Simulations are carried out in the case of complex harmonics,inter-harmonics and fundamental frequency fluctuations.Simulations were performed in the case of complex harmonic,inter-harmonic and fundamental frequency fluctuations,the simulation results show that under the condition of lower multiplication or convolution order,the new algorithm can obtain better parameter estimation precision than the classic algorithm based on self-multiplication window and self-convolution window.3.Aiming at the detection of dense harmonic parameters and the complexity of the algorithm,a harmonic detection algorithm based on double-window all-phase FFT(ap FFT)is proposed.,a harmonic detection algorithm based on double window all phase FFT(ap FFT)is proposed.Firstly,the process of all phase data preprocessing is introduced.Secondly,the spectrum of traditional FFT and ap FFT is compared,the results show that the discrete spectral lines in ap FFT spectrum are square and the phase is not change,which can better suppress the influence of spectrum leakage.On this basis,combined with Blackman window and two spectrum interpolation,a harmonic detection algorithm based on Blackman double window ap FFT two-spectrum interpolation is proposed,and the estimation formula of harmonic parameters is given.Experiments and comparative analysis are carried out with the traditional FFT method under dense harmonics,interharmonics and complex harmonics.The simulation results show that under the condition of small sampling length,the all-phase FFT method has less detection error for dense harmonics,inter-harmonics,and complex harmonic parameters,and it still has high harmonic precision in the case of fundamental frequency fluctuation.