Detection Of Transient Power Quality Based On Lifting Wavelet Transform And Implementation

In recent years, the application of non-stationary and sensitive equipments in electric power system is more and more extensive. On the other hand the electric power quantity of electric power system descends continuously,especially the electric voltage sag etc. non-stationary, transient power quality problem comes more seriously. On the other hand the customer increases continuously the request of the electric power quantity. Therefore there are very important and realistic meaning to the detection of the electric power quantity.Withdrawing the characteristic accurately, fixing position and dentifying the type of transient power quality signal,will provide useful basis to evaluate and manage the electric power quantity problem availably. But current common Fourier Transform etc. algorithm works invalidly to the detection of non-stationary, transient power quality signal. So the more valid method is in demand to realize accurate detection to transient power quality.Through reading a large amount of literature, the paper describes the research background and practical significance of the power quality detection, domestic and international research status of method and device to detect power quality. Wavelet transform has been widely used to detect and identify transient power quality because of its good time-frequency localization properties and the ability to deal with transient signals. This article has carried on the deep discussion on the continuous wavelet transform, discrete wavelet transform and lifting wavelet analysis. Contrast to the traditional wavelet transform, this paper analyzes the advantages of lifting wavelet transform theory in the field of detection of transient power quality,and uses9/7wavelet lifting scheme under the Matlab platform for the detection of voltage sag, voltage interruption, voltage swell, transient oscillation transient impulse etc.five common transient power quality disturbances. Results of Simulation show that9/7lifting wavelet can effectively detect the starting and ending times of disturbance.Based on the above research,this paper proposed and designed transient power quality detecting system. The hardware of the system includes the FPGA chip, the voltage conditioning circuit, anti-aliasing filter circuit, PLL circuit, the A/D sampling circuit. Part of the software is implemented through Verilog hardware describes language in the ISE integrated development environment,which is mainly composed of three parts sampling and controling module, memory module, lifting wavelet module. Consider the FPGA hardware resources and the specific needs of the system, the system uses a modified9/7wavelet lifting algorithm, improve and optimize liftfing wavelet coefficient to make it more easily implemented in hardware. The article using the ISE Simulator tool has carried on the simulation to lifiting wavelet module on function. The results show that the upgrade wavelet module can detect transient power quality disturbances effectively.Finally, this paper summarizes the work done and discussed the inadequacies of the thesis, the prospect for future research work.