Harmonic detection method based on Nuttall window four-spectral-line interpolation FFT (fast Fourier transform)

Abstract

The invention provides a harmonic detection method based on Nuttall window four-spectral-line interpolation FFT (fast Fourier transform). The method comprises steps as follows: (1), a time-domain signal is subjected to discrete sampling, a discrete signal sequence is obtained, a four-term three-derivative Nuttall window is selected to perform windowing processing on the discrete signal sequence, FFT analysis is performed, and a value of each discrete frequency point is obtained; (2), a maximum frequency point value and a submaximal frequency point value are selected nearby each peak frequency point spectral line according to the value of each discrete frequency point, a maximum amplitude spectral line and a submaximal amplitude spectral line nearby each peak frequency point spectral line as well as two peripheral spectral lines are found out according to the maximum frequency point value and the submaximal frequency point value, and amplitudes of the four spectral lines are obtained; (3), a amplitude correction formula, a frequency correction formula and a phase correction formula of four-spectral-line interpolations are derived according to the amplitude information of the four spectral lines. The spectrum leakage inhibition effect is good, the correction errors are small, and the harmonic analysis precision is high.

Description

Technical field [0001] The invention relates to a harmonic detection method, in particular to a harmonic detection method based on Nuttall window quadratic line interpolation FFT. Background technique [0002] Various non-linear devices in the power system bring a lot of harmonics to the power grid, leading to deterioration of power quality. In order to maintain the safe and stable operation of the power grid, high-precision detection of harmonic components is of great significance. [0003] At present, the most commonly used method of harmonic analysis is Fast Fourier Transform (FFT). When the frequency change of the signal under test causes asynchronous sampling, the FFT has a spectrum leakage phenomenon, which cannot accurately detect the amplitude, frequency and phase of the harmonics. And other parameters. The frequency of the power grid fluctuates, and it is difficult to achieve synchronous sampling even if the discrete phase-locked loop technology is used. The use of a wi...

AI Technical Summary

Problems solved by technology

The bispectral line interpolation algorithm uses two spectral lines near the frequency point of the peak spectral line, and introduces the frequency offset to obtain the parameters of the harmonics. Large correction error

The three-spectrum interpolation algorithm uses three spectral lines near the frequency point, which improves the utilization rate of leaked information, but this algorithm does not consider the information contained in the symmetrical spectral lines around the frequency point, and cannot use the symmetrical spectral lines to calculate the frequency offset. amount, which in turn causes the correction error to increase

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