Research On Comprehensive Evaluation Method Of Power Quality Based On Cloud Matter Model And Variable Fuzzy Set

With the development of power load diversity,a large number of non-linear loads and impulse loads are continuously connected to the distribution network,which will make the system power fluctuate in the constant value of voltage and frequency and affect the stability of AC wave,resulting in various power quality problems such as voltage fluctuation,frequency deviation,three-phase imbalance,etc.,leading to the continuous deterioration of power quality in the distribution network.Therefore,it is very important to establish a scientific and reasonable comprehensive evaluation model.Based on the introduction of the research background and research status of power quality comprehensive evaluation,thesis analyzes the evaluation standard,development trend and evaluation model of power quality comprehensive evaluation research in detail,and proposes two power quality comprehensive evaluation methods.The main research contents are as follows :(1)In view of the shortcomings of traditional matter-element analysis model which uses fixed value or interval to describe various features of things quantitatively,thesis proposes to integrate cloud theory model into traditional matter-element analysis model,and describe its features in three aspects of expectation,entropy and super entropy,so as to realize the mutual conversion of qualitative and quantitative in the process of power quality comprehensive evaluation,which is more reasonable To determine the power quality assessment level.In order to solve the problem of stochastic uncertainty in the process of solving the correlation degree,the results of power quality comprehensive evaluation are solved many times,and the expectation of multiple comprehensive evaluation results is used as the final evaluation result.At the same time,it can solve the fuzzy problem of evaluation grade boundary caused by the principle of maximum relevance degree in traditional matter element analysis model.In addition,the confidence factor is defined to reflect the discreteness of multiple evaluation values,so as to measure the reliability of evaluation results.(2)Aiming at the uncertainty of power quality comprehensive evaluation,a method of power quality comprehensive evaluation based on Set Pair Analysis and variable fuzzy set is proposed.Firstly,the power quality evaluation index system is established and classified,the subjective weight is determined by intuitionistic fuzzyanalytic hierarchy process.Secondly,according to the theory of set pair analysis,the sample data and each index grade interval are combined to form a set pair,and the relative difference function is constructed.Then a comprehensive evaluation method based on Set Pair Analysis and variable fuzzy set is established.Then combined with the eigenvalues of power quality status,the binary semantic method is introduced to carry out the secondary evaluation within the evaluation level,and further determine the power quality status of the evaluation samples.