Analysis Of Power System Harmonics Based On Wavelet Theory

With the development of modem industry, nonlinear loads of power system are greatly increased. The electrical characteristics of these nonlinear loads, including nonlinearity, impulsion and imbalance, which result in voltage aberrance. Voltage aberrance makes power quality severely worsen, endangers power system running safely and economically and affects some users working normally. The content of harmonic in power system is the important parameter in power quality. So, harmonic measurement is important significance in power system.Firstly, this paper systemic and brief introduces the concept of harmonic, hazard of harmonic, harmonic source and the traditional and new measurement of harmonic. Moreover, it discusses several important transform methods, such as Fourier transform, short-time Fourier transform, continuous wavelet transform, discrete wavelet transform and wavelet packet transform of which characteristics are analyzed. The key point is wavelet packet transform.Secondly, the design of filter is the basal problem in Digital Signal Processing. In this paper, the wavelet function is applied in FIR digital filter design as same as the common window function. The paper puts forward a superior and modified window function based on gauss window and cosine window. The simulated results with MATLAB show the strongpoint of this modified window function. It not only easy to design and realization, but also get best choice by adjusting parameter between stop-band attenuation and transition band, in order to get better matching between side-lobe extend and main-lobe width. So that, the filter designed using this modified window function can realize better result and reach the aim of digital filter. It is practicability.Again, to the study content, the paper puts forward the nonlinear method which eliminate noise based on wavelet packet theory, because the wavelet packet transform have more accurate ability which can analyses part signal. Furthermore, the paper study the steady and temporary signal based on reconstruction of wavelet packet decomposed coefficients and FFT transform. The temporary signal which passed pretreatment got better results using forenamed method. The simulated results with MATLAB show that the method of wavelet packet transform has better feasibility and advantages, solves limitation which traditional FFT arithmetic can not analyze time domain.In the end, this paper summarizes the study content, points out the shortage in study. Moreover, it makes a prospect on which applying the harmonics analysis in the power system.