paper:541 Analysis of non-stationary signals in power systems Zbigniew Leonowicz ABSP Lab., BSI, Riken (Japan) on leave from the Wroclaw University of Technology (Poland) Received the M.Sc. and PhD degrees in electrical engineering from the Wroclaw University of Technology, Poland in 1997 and 2001 respectively. The NATO Organisation awarded Dr. Leonowicz an Advanced Fellowship in 2001 and he spent this fellowship at the Technical University of Dresden (Germany). He has been with the Department

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... f Electrical Engineering at the Wroclaw University of Technology (Poland), since 1997 and with the Advanced Brain Signal Processing Laboratory, Brain Science Institute, Riken, Wako-shi (Japan), since 2003. His current research interests include modern digital signal processing methods. Abstract: Classical techniques to estimate the spectrum of the multi-component signal are based on Fourierbased transformations. The frequency estimates obtained from their spectral peaks are affected by the window length and phase of signal component, thus presenting a large variance even in the absence of noise. We estimate the spectrum of the signals with the help of the Wigner-Ville distribution (WVD) and we obtain its time-frequency representation. For the same purpose, the min-norm method (subspace method) is used. The accuracy and phase dependence of the tested methods were investigated and compared with the parameters of the frequency estimation via FFT. The proposed methods were also tested with nonstationary multiple-component signals occurring during the fault operation of inverter-fed drives and transmission lines.