An approach to power system harmonic analysis based on triple-line interpolation discrete Fourier transform

: The discrete Fourier transform (DFT) is a principal method for power system harmonic analysis. The fundamental frequency of the power system increases or decreases following load changes during normal operation. It is difficult to achieve synchronous sampling and integer period truncation in power harmonic analysis. The resulting spectrum leakage affects the accuracy of the measurement results. For this reason, a windowed interpolation DFT method for power system harmonic analysis to reduce errors was presented in this paper. First, the frequency domain expression of the windowed signal Fourier transform is analyzed. Then, the magnitude of the three discrete spectrum lines near the harmonic frequency point is used to determine the accurate position of the harmonic spectrum. Then, the calculation of the amplitude, frequency, and phase of harmonics is presented. The triple-line interpolation DFT can improve the accuracy of electrical harmonic analysis. Based on the algorithm, the practical rectification formulas were obtained by using the polynomial approximation method. The simulation results show that the fast attenuation of window function sidelobe is the key to reduce the error. The triple-line interpolation DFT based on Hanning, Blackman, Nuttall 3-Term windows has higher calculation accuracy, which can meet the requirements of electrical harmonic analysis.