Research On Comprehensive Evaluation Method Of Severity Of Voltage Sag

In recent years,with the investment and use of a large number of sensitive devices,voltage sag has gradually become one of the most important power quality problems.The voltage sag causes more and more industrial users to interrupt the continuous production process,causing major economic losses.In order to effectively carry out the voltage sag,it is undoubtedly important to carry out an accurate assessment of the voltage sag severity.This paper focuses on the calculation of voltage sag indicators and the comprehensive assessment of the severity of sags.Based on the traditional voltage sag index system,the effects of voltage sag on them are theoretically analyzed for sensitive devices such as programmable logic controllers,adjustable speed devices,computers and AC relays,established voltage sag tolerance curve for sensitive equipment.According to the different sensitivity of different devices,different indicators are used to calculate them,which can accurately reflect the impact of voltage sag on different devices.According to the basic parameters,state performance and response mechanism of source,network and load side,the voltage sag index system based on source,network and load is established.The traditional method of voltage sag severity assessment is subjective in choosing the weight of each index,which makes the evaluation results lack of pertinence for the guidance of voltage sag control work.This paper presents a comprehensive assessment method for voltage sag based on multi-objective decision analytic hierarchy process(AHP).Firstly,the superiority of each index of voltage sag is calculated,and the superiority matrix is constructed.On this basis,the objective weight of each index is determined by using the method of maximum dispersion,which is used as the judgment of the relative importance of each index in the analytic hierarchy process.Finally,the weight of each index is calculated by the analytic hierarchy process,and the weight of each index and the degree of superiority are linearly weighted to obtain the severity of the voltage sag at different observation points.This method combines the multi-objective decision-making method with the fuzzy analytic hierarchy process,comprehensively considers the subjectivity and objectivity of each index,makes up for the shortcomings of the traditional analytic hierarchy method,and helps to promote the voltage sag in various regions.Based on the monitoring data of a voltage sag event suffered by a lOkV voltage level in an industrial park in Hubei Province,the above method is verified by the example.By comparing with the traditional analytic hierarchy process,the correctness and feasibility of the proposed method are verified.