Method for detecting harmonic waves of electric system based on window and interpolated FFT

Abstract

The invention discloses a method for detecting harmonic waves of an electric system based on window and interpolated FFT. The method comprises the following steps of obtaining sampling data of detected signals by an analog to digital converter, carrying out an operation of adding Hanning window FFT on the sampling data, searching a peak and an adjacent secondary peak of a spectral line to obtain an interpolation coefficient of a fundamental wave, obtaining the interpolation coefficient of each level of harmonic wave by the interpolation coefficient of the fundamental wave, eliminating the interference of the fundamental wave frequency spectrum to the adjacent harmonic wave frequency spectrum to modify the spectral line of the harmonic wave, and finally obtaining the frequency, the amplitude value and the phase of the fundamental wave and each level of harmonic wave by an interpolation operation. The invention firstly puts forwards that a real spectral line of the harmonic wave can be obtained by eliminating the interference of the fundamental wave frequency spectrum to the adjacent harmonic wave frequency spectrum in the Hanning window FFT spectral line. The scheme of the invention has the advantages of providing the method for detecting the window interpolated FFT harmonic wave with a small calculation amount and high analyzing precision.

Description

technical field [0001] The invention relates to the field of harmonic detection in power systems, in particular to a method for detecting harmonics in power systems based on windowed interpolation FFT. Background technique [0002] Power system harmonics affect the normal operation of power equipment, and accurate detection of harmonics is a basic requirement for the safe and stable operation of power grids and power equipment. Windowed interpolation FFT (Fast Fourier Transform) method is a common method for harmonic detection in power systems. In non-synchronous sampling, Fourier transform has spectral leakage and fence effect. The windowed interpolation FFT suppresses the spectrum leakage through the windowing operation, and eliminates the influence of the fence effect through the interpolation operation. Cosine window functions commonly used in windowed interpolation FFT methods include Hanning window, Blackman window, Blackman-Harris window, Rife-Vincent window, optima...

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Problems solved by technology

[0003] The disadvantage of the existing technology is that the windowed interpolation FFT method can only suppress the spectrum leakage, but cannot eliminate the spectrum leakage

[0004] The disadvantage of the prior art is that the windowed interpolation FFT method based on the window function with a small number of items has a small amount of calculation, but the analysis accuracy is low; the windowed interpolation FFT method based on the window function with a large number of items has high analysis accuracy, but the calculation large

However, the window function with fast side lobe attenuation must have a wide main lobe, and the two are always contradictory

Among the above window functions, the Hanning window is a two-term coefficient cosine window. Its interpolation formula is simple and clear, and the calculation amount is small, but the analysis accuracy is low; the number of other window functions is more than the Hanning window, and the analysis accuracy is higher. The multinomial window function makes the interpolation algorithm complex and the amount of calculation increases

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