Research On The Application Of Fractional Fourier Transform In Transient Signal Of Power System

On the basis of a new tool for time-frequency analysis, Fractional Fourier Transform(FRFT), this paper studied and analyzed the recognition of power quality (PQ) disturbances and the partial discharge (PD) signal extracting in power system. In sum, the work in this paper is as follows:1. The paper investigates a new method using Fractional Fourier Transform(FRFT) with Wavelet Entropy for recognizing the signals of PQ disturbance based on the characteristics of PQ signals. The classification and recognition of power quality disturbance signals which are researched by the scholars at home and abroad are always the hot issues in Power System. The Wavelet Entropy which is based on Wavelet analysis is better for feature extraction, it can be used to recognize the signals of power quality disturbance. But The Wavelet Entropy is not sensitive to the noise under certain conditions of SNR, so the scope of application is limited. Transform the signals of power quality with white noise by FRFT to eliminate the coupling of the noise, then using the Wavelet Entropy to analyse the disturbances. This new method is more flexible and more capable of discrimination, when the SNR is lower, the Wavelet Entropy will not be affected by the noise, its robust is wide.2. According to the characteristics of PD, the paper investigates a new method using Fractional Fourier Transform(FRFT) for denoising PD at the weak noise condition. Transform the PD with white noise by FRFT, In Fractional Fourier domain, FRFT spectrums of PD signals show different time-frequency congregation following with the change of order. The algorithm for scanning the optimal order of FRFT according to the minimum mean square error (MMSE) criterion is derived and 3σrule is introduced to deal with the noise signals by the Noise intensity from Wavelet Transform, so the noise can be depressed. Compared with the conventional wavelet based denoising algorithms, the new algorithm is more flexible and obvious in effects of simulated process.The simulation and example analytical results indicate that the method proposed in this paper can extract the parameters of non-linear and non-stationary signals accurately, it can be achieved effectively and gives a new approach for the analysis of the Power system transient signal.