Research On The Evaluation Method Of Voltage Sag Based On Comprehensive Informat Ion

With the transformation of power industry technology and the development of social production and life,a large number of non-linear loads and sensitive electrical equipments are connected to the power grid,which increases the number and harm of disturbance events in the power system,and the power quality problem becomes more and more serious.To ensure reliable power supply and high power quality is one of the key points in the field of power technology.Voltage sag is the one with the highest frequency and the worst impact on power consumers among all kinds of power quality problems,it is the most representative power quality disturbance event and has attracted wide attention of power scholars.Accurate and timely comprehensive evaluation of voltage sags is one of the preconditions and key factors for optimizing dispatch and reducing resource cost with limited manpower and material resources,and at the same time,for more effective control of voltage sag hazards,which has extremely important significance of engineering application.This paper first introduces the related concepts and classifications of power quality,describes the domestic and foreign research status of voltage sag assessment,and then focuses on the definition and detection methods of voltage sag.In this paper,the selection of parameters and the establishment of model in the comprehensive evaluation of voltage sag are elaborated in detail,and a universal comprehensive evaluation method is presented and improved.The main work is as follows:(1)The evaluation indicators are selected and divided,and a general voltage sag evaluation model is established.Traditional voltage sag assessment methods usually use the sample data of single attribute or index to calculate the corresponding evaluation results,or only focus on the single factor in the areas of voltage sag,and there are differences in the evaluation methods which are not comprehensive and universal for voltage sags in different systems.On the basis of traditional voltage sag assessment,this paper converts voltage sag comprehensive assessment into multi-criteria decision-making problem,comprehensively analyses the influence of characteristic variables on the severity of voltage sag,and reasonably chooses six characteristic variables,namely,sag depth,duration,phase angle jump,sag slope,voltage level and total harmonic distortion rate,as indicators of comprehensive assessment.According to the importance and similarity of indicators,the hierarchical structure is classified,and the general evaluation model is established.(2)An improved evaluation method based on fuzzy preference programming extended fuzzy analytic hierarchy process is proposed for voltage sag comprehensive evaluation.Based on the traditional analytic hierarchy process,this method combines the fuzzy theory,uses triangular fuzzy number to replace the compulsory quantitative fuzzy semantic evaluation,and introduces tolerance coefficient into the fuzzy interval,overcomes the shortcoming of adjusting the subjective evaluation of decision-making when the judgment of the fuzzy interval is inconsistent,provides a flexible tolerance interval to reduce the complexity of the evaluation process and minimize the judgment error.At the same time,the fuzzy preference programming is introduced to improve the fuzzy analytic hierarchy process,and the weight calculation of indicators and factors is transformed into a non-linear optimization problem,which solves the problem that the optimal priority vector can not be determined when the multiple weight vectors satisfy the consistency judgment of the fuzzy interval.Combining with the health index theory,the evaluation criteria of indicators are divided in detail,the visual evaluation results are uniformly described.The evaluation results in the analysis of case show that the evaluation model and method are comprehensive and universal.(3)A comprehensive evaluation method of voltage sag based on subjective and objective information is proposed.Based on the fuzzy preference programming extended fuzzy analytic hierarchy process,multi-decision makers are used for subjective evaluation in this method,which solves the problem of strong subjective bias and low accuracy of single decision maker,and improves the information entropy weight method to calculate the objective correction weight of weight sample.At the same time,the improved method based on Jousselme evidence distance is used to fuse subjective and objective weight information to solve the situation where the evaluation results may be contrary.The result of fusion weight is more reasonable and the evaluation model is more accurate.The correctness of the combination of information fusion theory and voltage sag comprehensive evaluation and the rationality of the revised weights are proved in the studies of cases.