The Analysis Of Power Quality Disturbance Based On Wigner-Ville Distribution

Power quality disturbances detection is becoming one of the most important subjects in modern power system. It is very important to find out the power quality disturbance in order to improve power quality. When accident or fault occurs in the system, the sampled signals always include short impulses or rapid changing components. These components often contain very useful information for detecting the important characteristics of the abnormal moment in time. However, the electrical signals sampled from the real power system are often unstable, and the power quality disturbances often appear crosswise. Wigner-Ville distribution is an excellent algorithm to analyze the non-steady signal by joint time-frequency analyzing. So The Wigner-Ville distribution is introduced in the thesis as a new signal-processing tool for power system signal detection.This thesis focuses on power quality disturbance detection using Wigner-Ville distribution algorithm. The main works are as follows:1. Chapter 1 presents the definition, causes, classification, and evaluation criterion of power quality problems. Three transform based methods for power quality analysis algorithms are compared. An introduction to some software packages for analyzing electric oscillation, including Matlab and PSCAD/ETDC, is made at the end of this chapter.2. Chapter 2 first analyses the joint time-frequency distribution and then the Wigner-Ville distribution is presented. The principles of the continuous Wigner-Ville distribution, the discrete Wigner-Ville distribution, the coss-term interference and the method to reduce it, the excellent characters of the Wigner-Ville distribution and Mallat algorithm are discussed in detail. It provides a useful tool for measurement of the power quality disturbances.3. Chapter 3 discuses the main principle of harmonics and interharmonic detection with the Wigner-Ville distribution. The harmonic components are accurately estimated via the Wigner-Ville distribution with its frequency marginal condition property. 4 Chapter 4 analyze the main principle of short time power quality disturbance detection with the Wigner-Ville distribution. The harmonic components are accurately estimated via the Wigner-Ville distribution with its frequency marginal condition property. With the frequency and time marginal condition properties, the short time power quality disturbances can be located accurately. Finally, the method to detect the crossed power quality disturbances via Wigner-Ville distribution is presented.5 Chapter 5 is a summary of the thesis.To enhance the power quality, it is the first thing to detect and classify the power quality disturbances and then take counter-measurements. In this paper, a new algorithm for measuring power quality disturbance was discussed in length. Through simulations and comparison, extensive research was made on the Wigner-Ville distribution applicable for harmonics and interharmonic measurement, and the short time power quality disturbances detection. At last, a conclusion is made and some further research problems are pointed.