Spektral Leakage Elimination of the Fourier Transform of Signals with Fundamental Frequency Deviation

In this paper a spectral correction based algorithm for spectral component determination based on DFT is proposed for especially highly fluctuating fundamental frequency cases. When DFT is used with a standard window length at a multiple of the fundamental period assuming the nominal frequency does not change, interharmonics which actually do not exist in the spectrum appear due to the grid-effect of the DFT algorithm. The proposed method uses a synthetic waveform produced at the fundamental frequency and amplitude to determine the amount of the leakage at each frequency and the leakage is subtracted from the original DFT of the signal to correct the frequency spectrum. It has been shown on both simulative and field data obtained from 50Hz-power-system that if the fundamental frequency is detected precisely, it is possible to avoid the leakage completely and obtain correct interharmonic amplitudes around the fundamental frequency.