Study On Detection And Analysis Of Transient Power Quality

With the pervasion of power electronics apparatus and nonlinear loads, recently the power quality problems have been more and more deteriorated by the distorted waveform of voltages and currents in power network. Traditional power quality analysis is based on virtual value theory. As a frequently used analysis tool, Fourier transform is not suitable for the non-stationary signals processing. Thus new analysis methods are required to detect, identifyand evaluate power quality disturbances accurately.In this dissertation, the recent interest in power quality is introduced from two aspects-the definition and the art of the state of study on the power quality. Several key issues, such as power quality disturbance localization, dynamic detection of harmonics and intel-harmonics, measure reactive power, transient disturbances analysis and power quality disturbance signal compression are comprehensively and thoroughly studied and analyzed in this thesis. The main contribution is given as follows:1. A fast transient power quality disturbances localization approach is presented by using Hilbert transform combined with backward difference. Based on detection of the disturbance signal envelope, the approach is implemented by using backward difference to detect signals distortion point. The experimental results demonstrate that this approach possesses the merit of simplicity, speediness and accuracy. And it provides some support for the analysis of disturbance signal and further improvement.2. For the purpose of detecting harmonics and interharmonics, a method is proposed based on the time-frequency analysis method—S-transform. The reason for the superiority of S-transform are due to the fact that the width of a modified Gaussian window is a function of inverse frequency. The experimental results show that this method can detect harmonic and interharmonics effectively.3. A novel method is proposed by using S-transform and Hilbert transform to measure reactive power based on the definition of Budeanu in nonsinusoidal conditions. It is achieved by means of S-transform and shifting 90 degree of Hilbert-transform. The results of simulation and measurement of real power system show that this method is of high accuracy and can meet the needs of practical application.4.Through analyzing the time-varying and non-stability of transient power quality, two indices of transient power quality named fundamental frequency component distortion ratio and disturbance component ratio are proposed, which adopt HHT to analyze transient power quality disturbances. Simulated and real experiments show our approach is feasible in detecting transient indices of power quality.5.For a massive of power quality disturbance data stored and transmitted, a new data compression method is proposed. The test cases indicate the validity of this new method, with which Signal-to-Noise ratio can keep well and the compression ratio is satisfied.