A contribution for the measuring process of harmonics and interharmonics in electrical power systems with photovoltaic sources

Resumo

© 2018 Elsevier LtdThe main standards for quantifying waveform distortions in power systems are based on the Discrete Fourier Transform (DFT) through the use of a rectangular time-window of fixed length. However, limitations and imprecisions of the DFT related to the analysis of time-varying signals, typical of environments with renewable sources, have been reported in the literature. This study presents a methodology for identifying the most appropriate time-window length to quantify the emissions of harmonics and interharmonics, considering time-varying signals. The methodology in question is substantiated on the calculation of the harmonic and interharmonic distortions using the DFT according to IEC 61000-4-7 and employing the spectral components acquired from the application of the Prony method and Kalman Filter. It is tested in view of the current signals measured in a real grid-connected photovoltaic installation. The methodology proposed in this work improves the accuracy of the harmonic and interharmonic quantification process using DFT by selecting a proper time-window length, and in addition, identifies the error attributed to the use of a 200 ms time-window length, as premised by the IEC 61000-4-7.

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