Power Quality Evaluation Of Distribution System Based On Subjective And Abjective Weights

With the development of the national economy and the continuous expansion of the industrial scale,the importance of electric energy in all walks of life is growing.At the same time,the requirements for power quality are getting higher and higher.However,with the continuous access of new power electronic devices,the nonlinear load is increasing day by day,and the pollution of power quality is becoming more and more serious.A scientific and effective evaluation of power quality is particularly important.This thesis first analyzes the current research status of power quality assessment at home and abroad,then introduces the definition of power quality and the national standard of electrical energy index.Through the analysis of the comprehensive evaluation methods and research status of power quality at home and abroad,the main research contents of this thesis are as follows:(1)Aiming at the influence of rolling mill system on power quality of power grid under different working conditions,a power quality evaluation method based on variable fuzzy set is proposed.The method uses variable fuzzy set theory to conduct a comprehensive evaluation on three working conditions of the rolling mill system.Firstly,the electric energy index that has great influence on the power quality during the operation of the rolling mill is selected,and the evaluation index system is established.The evaluation interval matrix and the variable range evaluation interval matrix of each index are determined according to the national standard of China.By evaluating the interval matrix,the point value matrix with membership degree equal to 1 is established and the relative membership degree of each index is calculated.According to the relative membership degree of the index,the comprehensive membership degree of the power quality to each evaluation grade under each working condition of the rolling mill is calculated.For the problem of weight distribution of different indicators,the combination weighting method is selected to empower each index,so that the weight of each index is closer to the actual working condition of the rolling mill.Finally,the applicability and rationality of the method are verified by specific cases.(2)Aiming at the shortcomings of the traditional radar map,based on the traditional radar map,a power quality evaluation method for power distribution system based on improved radar map is proposed.The method uses the minimum deviation combined weight method to calculate the optimal combination weight of each evaluation index.Based on the traditional radar chart,the determination of the angle between the axes of each index and the selection of the feature vector are further improved.First,the original triangular area is replaced by a sector area and the angle between the axes of each index is calculated by the minimum deviation combined weight method.And the new feature vector is selected to construct the evaluation function and the power quality of the power distribution system is comprehensively evaluated by calculating the evaluation function value.Compared with the traditional radar chart,the improved radar chart method solves the problem of information sharing between the indicators and the non-unique evaluation result in the traditional radar chart method,which makes the evaluation result more accurate and reasonable.