The Research On The Harmonic Characteristics Of Nonlinear Loads In Power System

In recent years, with the rapid development of power electronics technology and wide application of nonlinear devices, the harmonic resources of power system increase rapidly, which make a severe influence on the secure and economic operation of power system and its users. Therefore, the harmonic problems in power system have been received great concern from all over the world. The detection of harmonic resources is an important aspect of harmonic analysis. The research on the harmonic characteristics of different harmonic resources, comprising various nonlinear devices and the abstraction of corresponding harmonic characteristic parameters are the basis of the detection of harmonic resources.Firstly, the general principle of three different analysis methods, which are usually used in the analysis of signals in power system, is presented in this paper. According to the general principle and exploitation condition of the analysis methods, the advantage and disadvantage of the three different methods are compared and discussed. Then, according to the nonlinear characteristics of various nonlinear devices, major harmonic resources can be categorized as devices that generate harmonics because of saturation of iron, devices that generate harmonics due to their nonlinear voltage-current characteristic and power electronics devices that generate harmonics during their switching process. The operating characteristics and the causes that make the harmonics generated of these nonlinear devices are also presented in the paper. The harmonic signals, which will be analyzed, are obtained by simulating the working characteristics of those devices through doing experiments and simulating in ATP .The harmonic current signals of different nonlinear devices are analyzed by using three analysis methods, which are Fast Fourier Transform (FFT), the Muti-resolution Analysis of Wavelet Transform (WT) and Fractal analysis. Different characteristic parameters, such as total harmonic distortion, crest factor, form factor, the peak point of the energy distribution of signals and the box dimension, are chosen and calculated through Matlab. At the end of the essay, the author analysis the physical meaning of the different devices. The characteristic parameters of different devices are integrated, and a new criteria to distinguish different nonlinear devices is proposed.