Short-time Fourier transforms and Wigner-Ville distributions applied to the calibration of power frequency harmonic analyzers

This paper is concerned with the measurement of nonsinusoidal waveforms, in particular the use of waveform transforms in the calibration of power frequency harmonic analyzer instruments designed to make harmonic measurements under nonstationary conditions. The suitability of the Fourier transform (FT) for the analysis of nonstationary waveforms is discussed. A method involving windowing of the waveform data known as the short-time Fourier transform (STFT) and its application to harmonic amplitude measurements is considered. Limitations in time and frequency resolution inherent in the STFT lead to the development and investigation of the Wigner-Ville Distribution for use in this application. The performance of the various transforms are compared by simulation. Results using a test signal, typical of a practical signal encountered by harmonic analyzers, are presented for each transform.