Subharmonic measurement using DFT and Wavelet-Packet Transform in an IEC extended framework

This paper proposes two different methods for measurement of subharmonic components in voltage and current waveforms in power systems. The paper first proposes a definition of the subharmonic group compatible with the standard of the International Electrotechnical Commission IEC 61000-4-7, as a grouping of spectral bins lower than the fundamental frequency resulting from the application of Discrete Fourier Transform. Then it presents a new method based on the Wavelet-Packet Transform to compute the magnitude of this subharmonic group. The performance of the two methods are compared in different measurement conditions.