Studies On External Network Equivalent Parameter Estimation Method And Its Application In Static Voltage Stability Analysis

Modern power system is increasingly becoming a large-scale and complex network.The power system’s transmission pressure is more and more seriouse with theincreasing needs of electricty for the load terminal. When the transmission capacity ofthe system is toward the limit, It’s easy to cause voltage instability accident, lead touser’s power outage, and even seriously affect people’s production and life. Therefore,it’s necessary to assess the status of the system voltage stability fastly, accurately andeffectively.At present, there have been a lot of research about the static voltage stabilityassessment method. The continue power flow method and the global or local voltagestability index have emerged. Compared with continue power flow and the global index,the local index has some advantages-based on the measured data of the local grid;needn’t the flow calculation based on entire network; need small amount of calculation;the calculation speed is fast; with wide application in online analysis and assessment ofthe voltage atability. However, due to that the local index need to consider the affect ofexternal network to monitoring component though the external network equivalent,therefore, the accuracy of external network equivalent directly affect the correctness andeffectiveness of the local index. Studies in the paper focus on the method of externalnetwork equivalent parameters estimation and its application in the analysis of staticvoltage stability, there are the main works as following.①Beginning with the thevenin equivalence’s physical meaning, the paper in-depthunderstands the physical characteristic of the thevenin equivalent parameters, anddiscuss of the approximate relationship between the thevenin equivalent parameters andsystem’s short-circuit impedance parameters. The paper has analysised the estimatetheory and method of a few typical estimation method of the thevenin equivalentparameters. The approximation principle and the possible problem in practicalapplications of various methods have been also disscussed in this paper. We have takeninto account the effect on the equivalent parameter estimates because of the differentload models, different load growth step and measurement error. And then, we presentedthe applicable conditions of the related estimation methods.②Considering the thevenin equivalence’s physical meaning, the paper proposed anleast squares optimizated estimation model of the thevenin equivalent parameters based on the single measured data of the monitored line. The model can use the good filteringeffect of the least squares to reduce the impact of measurement error on the equivalentparameter estimate result. The model also can avoid the problem of multiple solutionsvia the physical feature constraint of equivalent parameters. The paper use thesemi-smooth network method which can be able to identify inequality constraintseffectively for solving the constrained optimization model, and then analysis the staticvoltage stability(including continuous flow calculation and static voltage stability index)of the equivalent network.③The correctiness criterion of thevenin equivalent parameters’ estimates and theadaptive of existing categories thevenin equivalent parameters estimation method havebeen proved in the simulation analysis with IEEE systems. With RTDS systemplatform，via the applied research of equivalent method in the static voltage stabilityanalysis（including continuous flow calculation and static voltage stability indexcalculation）, the correctness and effective of the model have been proved through thecomparing of the static voltage stability to the former static voltage stability of thenetwork.