【作者】 刘安定；

【导师】 肖先勇；

【作者基本信息】 四川大学 ， 电力系统及其自动化， 2005， 硕士

【摘要】 随着国民经济的迅速发展和电力市场的逐步形成,电能质量问题已经成为众多领域关注的热点。必须建立电能质量检测和分析系统,实现对各种电能质量问题的故障定位和特征提取。这是治理和改善电能质量的必要前提和依据。 本文首先阐述了电能质量的相关概念,介绍了各种电能质量现象及相关标准。其中,对几种有代表性的短时电能质量扰动作了详尽而细致的描述,分析了它们的扰动特征,分别是:电压凹陷、电压凸起和电压中断;短时间谐波和时变谐波;高频暂态扰动,包括暂态振荡和暂态脉冲等。 目前的电能质量检测和分析方法大致可分为时域仿真法、频域模拟法和基于变换的方法。小波变换作为第三类方法中的典型,近年来已成为各专家和学者的研究热点。但电能质量问题种类众多,且扰动特性各有不同,现有方法虽然各有其特点,但还不足以很好解决对各种电能质量扰动特别是短时电能质量扰动的检测,尚需进一步研究和完善现有的检测与分析方法。本文提出了将局部余弦变换引进到电能质量检测领域,结合现有检测和分析方法,重点研究和探讨了局部余弦变换和小波变换的分析方法。 结合小波检测中的两个难点一时变谐波检测和信号噪声问题,具体研究了如何将局部余弦变换应用到电能质量扰动信号的检测和分析。 首先探讨了如何利用局部余弦变换和差变算法实现噪声环境下的短时电压变化的检测。 然后研究了如何利用局部余弦变换对信号时频的划分实现对短时谐波的检测分析以及如何通过局部最佳余弦基的搜索分析时变谐波。更多还原

【Abstract】 With the rapid growth of national economy and formation of power market, power quality has become the focus of many fields. It is necessary to set up power quality monitor and analysis system, which can realize fault location and character extraction to all power quality disturbances. It is the premise and reference of improve and harness power quality.Firstly this paper expands relative concept about power quality, introduces all power quality issues and their standard. Among those several representative short-term power quality disturbances are introduced particularly, and their characteristics are analyzed. They are: voltage sag, voltage swell and voltage interruption; transient harmonic and time-varying harmonic; transient disturbances, including transient oscillation and transient pulses.Generally power quality detection methods can be generalized in three types: time domain simulation, frequency domain simulation and methods based on transform. Wavelet transform has become study focus of many experts and scholars as representative of the third type. However, power quality issues have many types, and they have different characters. Sometimes wavelet transform can’t treat all power quality issues especially short-term power quality disturbances. It is necessary that add other method to make up the shortage of wavelet transform. This paper introduces local cosine transform (LCT) to power quality detection. This paper expounds fundamental principle and time-frequency character of wavelet transformand local cosine transform.We discuss how to apply local cosine transform to power quality disturbance detecting considering two difficulty in wavelet analysis - time-varying harmonic detection and signal noises.Firstly we discuss how to detecting fundamental frequency disturbances in noises through noises robustness of LCT coefficients and difference algorithm.How to use local cosine transform to detect short time harmonics, how to search LCT optimum base to analyze time-varying harmonic are emphasis of this paper.Finally we explain how to utilize wavelet transform module maximum filtering signal noises and analyzing high frequency transient disturbances.After simulation and comparing with other methods we know this method has preferable performance. Analyzing power quality issues using this method can get satisfactory results. This method makes up the singleness and shortage of wavelet analysis in power quality detection. It provides a new approach in this field.In the end we point out some place need improving of this method.更多还原