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Research of Nonsinusoidality in Smart Grid via Short-time Fourier Transform

The article is devoted to the study of higher harmonics and interharmonics in a Smart Grid with thyristor voltage regulators and distributed generation sources. The analysis of various methods for assessing the electrical network nonsinusoidality is carried out. It is established that the most suitable method is based on the short-time Fourier transform. Various window functions are analyzed and their comparative characteristics are given. The following criteria are selected to evaluate the effectiveness of windows: main-lobe beamwidth and peak sidelobe; maximum conversion losses; dependence of the frequency offset on the noise level; errors in estimating the frequency, amplitude and phase of the harmonic. The Chebyshev window turned out to be the most effective for evaluating interharmonics in the Smart Grid. Simulink model of the Smart Grid segment has been developed, on the basis of which the amplitude-frequency spectrum of higher harmonics and interharmonics is obtained. The research results have shown that the short-time Fourier transform using the Chebyshev window successfully solves the problem of estimating nonsinusoidality in a Smart Grid.