Cálculo de harmônicos e inter-harmônicos baseado na norma IEC 61000-4-7

Abstract

The harmonic and interharmonic components calculation is usually performance by using the FFT ( Fast Fourier Transform). However, through the use of this tool, some problems may arise due the fact that the original signal energy can spread over the frequency spectrum, promoting the appearance of not actually existing components. This phenomenon is defined as spectral leakage and happens because either there is some interharmonic component whose frequency does not match the frequency resolution of the FFT, or because the signal is sampled asynchronously. In the first case, IEC 61000-4-7 provides the groups and subgroups approaches to include the interharmonic energy spreads over the frequency spectrum. In the case of asynchronous sampled rate, interpolation methods are presented both in the frequency domain and in time domain for correcting the result obtained through the FFT. Thus, this work addresses IEC approach and presents how the time and frequency interpolation can be used to improve the IEC criteria. The interpolation methods are compared in order to find the best method to be applied for the calculation of the components contained in the signal, in accordance with IEC 61000-4-7.