Analysis of non-stationary signals in power systems

Classical techniques to estimate the spectrum of the multi-component signal are based on Fourier-based 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. The spectrum of the signals is estimated with the help of the Wigner-Ville distribution and its time-frequency representation is obtained. For the same purpose, the min-norm method (subspace method) is used. The accuracy of the tested methods was investigated and compared with the parameters of the frequency estimation via FFT. The proposed methods were also tested with non-stationary multiple-component signals occurring during the fault operation of inverter-fed drives and transmission lines.