Study On The Application Of Wavelet Transform In The Analysis Of Power Quality Disturbances

It is an essential cause bringing about power quality's decline that the steady-state or the non-steady-state disturbing signals exist in power network, so they must be main monitoring objects of power quality in power network. For a long time, the Fourier transform (FT) and the windowed Fourier transform (WFT), often called the short time Fourier transform (STFT), possess a leading position in signal analysis, but because of their inherent defects, they can not be used to effectively analyze non-steady-state disturbing signals of power quality. The wavelet transform (WT) springing up in the end of the 20th century gives a new method for studying power quality's disturbing signals. The wavelet transform, compared with FT or STFT, has two outstanding traits: there being no regular core function and its changeable time-frequency window. The former, on the one hand, makes the result of wavelet transform strongly rely on the properties of wavelet function being used (WF), but on the other makes it possible that the results of wavelet transform are improved with cease. The latter brings wavelet transform having the superiority of analyzing non-steady-state signal, with which the traditional methods are incomparable. All the merits make wavelet transform can be a vigorous analysis tool in a number of the fields such as the analysis of power quality's disturbing signals in power network.When using wavelet transform for analyzing different problems, how to choose the best wavelet function is the most important factor to determine and improve the application effect of wavelet transform. Proceeding from the properties of wavelet function and different types of wavelet transform, the detection and the location of the same power quality's disturbing signals are investigated carefully by making use of real continuous WT, real discrete orthonormal WT, complex continuous WT and complex discrete orthonormal WT, in this paper, and the analysis results are compared completely and some factors affecting the detection and the location precision are studied thoroughly. As a result, it is revealed that different forms of wavelet function, when used for detecting and locating the same kinds of power quality's disturbing signals, exist in the difference in the detection and the location precision and sensitivity. At the same time, the choice principles what is the best wavelet function...