Measuring Method of Harmonics and Interharmonics Based on Ratio Correction and Matrix Inversion

Abstract

With the power electronic devices densely connected to the power grid, it is easy to make the interharmonic which is close to the harmonic appear in the power system signals. When the frequency of interharmonic is close to that of harmonic, the spectrum of interharmonic will leak to the harmonic spectral line, and generate serious main lobe interference with the spectrum of harmonic, which will make the performance of current detection methods based on discrete Fourier transform or fast Fourier transform (DFT/FFT) algorithm invalid. Based on the specified signal processing recommendations by IEC61000-4-7, this paper proposes a ratio correction method based on the interharmonic leakage estimation to detect adjacent interharmonic and harmonic. Firstly, the characteristics of spectral interference between the harmonic and the interharmonic under fundamental frequency synchronous sampling are analyzed in this paper. According to the characteristics of the interharmonic leakage on each spectral line, the spectral values of interharmonic on the harmonic spectral line can be estimated by solving the spectral line equations, which are constructed by using the interharmonic spectral lines around the harmonic spectral line. And the frequency parameters of the interharmonic will be obtained by using the ratio correction algorithm. Secondly, considering the influence of the interharmonic spectral leakage on amplitude and phase detection, according to the estimated frequencies, the amplitude and phase parameters of each component can be corrected by using the incidence matrix inversion algorithm, which is constructed by the window spectral function. Finally, the theoretical simulation example and the practical simulation example analysis of the proposed method are carried out on the MATLAB simulation platform. The results show that the method proposed in this paper can effectively suppress the influence of the interharmonic spectral leakage, and it can rapidly and accurately detect the parameters of adjacent harmonic and interharmonic based on a limited data length of samples.