Power System Transient Stability Critical Clearing Time Regression And Application In Transfer Capability Calculation

The transient stability assessment(TSA)and control of power systems plays an important role from both economic and reliability point of view.The power system should remain transiently stable and capable of withstanding a wide range of disturbances in order to supply reliable service to consumers.In nowadays high-volume and time-varying systems,it is a challenge to maintain the system security due to the transmission systems operating close to their physical limits.The aim of TSA is not only to predict the transient behavior of the system for the set of "pre-checked" operating states/points.TSA should also reflect the capability of the power system to regain synchronism after an occurrence of a large disturbance for operating states that are "new".Research content 1:Multi-state Critical Clearing Time Regression and CCT Limited Operation Point Boundary ConstructionTo overcome the lack of functional relationship that connects system parameters with some sort of transient stability index(TSI),To overcome the issue that the existing transient stability assessment methods only focus on one fault or one operating point,this thesis proposes a novel methodology for multi-state critical clearing time regression in the parameter-space.This method presents the functional expression for the mapping between critical clearing time(CCT)and power parameters,which combines thresholds to construct parameter space system CCT constrained operating point boundary(CCTL-OPB).The CCTL-OPB is defined as the boundary of all the stable operating point in the parameter-space for the given contingency and the system topology before and after the fault.Firstly,based on the mechanism of CCT Limited Operation Point Boundary construction,this thesis expounds the theoretical basis of constructing parameter space CCTLOPB using the operating state parameters of the pre-fault system.Then,based on the Broad Learning System,the mapping relationship between the critical clearing time and the power system parameters is constructed,and the CCT Limited Operation Point Boundary is determined by combining the pre-set fault clearing time threshold.Research content 2:Improved Construction of the CCT Limited Operation Point BoundaryIn order to support online transient stability assessment and preventive control(Transient Stability Assessment and Control,TSA&C),the parameter space CCT Limited Operation Point Boundary construction method should meet the following requirements:1)CCTL-OPB is expressed by the parameters of the operation state of the system before the failure.2)CCTL-OPB is at least second-order differentiable.In the preventive control model with transient stability constraints,the first and second order partial derivatives can be provided if the constraints need to be modified.3)Ensure that the radical situation of transient stability assessment is minimized4)In order to ensure the adaptability of the evaluation model,it is necessary to ensure the generalization performance of the prediction model.In research content 1,the constructed CCTL-OPB satisfies the above conditions one and two.Furthermore,on the basis of the model,the remaining condition 3 and condition 4: 1)the radical result of the stable boundary is minimized;2)after the emergence of the new operating point(sample),the model is updated and extended,which is first analyzed.Then,the critical error correction and incremental learning strategy are proposed to improve the model of the above problems.Then,the model is verified in the test system and the actual system.Research content 3:Transient Stability Constrained Total Transfer Capability Calculation(TSC-TTC)The optimal power flow model is constructed based on the branch power flow method,and its rationality is proved by transforming the model into a convex optimization model with second-order cone form.Then,the key fault transient stability constraints are constructed based on the parameter space CCT Limited Operation Point Boundary,constructed by research content 1 and 2.Finally,the constructed transient stability constraints are transformed into exponential cones to ensure the convexity of the optimization model.The method realizes the calculation of the Transient Stability Constrained Total Transfer Capability Calculation(TSCTTC).It provides decision-making reference information for the dispatchers,so that the system can meet the power load demand of each region to the maximum extent.Research content 4:Transient Stability Constrained Total Transfer Capability Calculation Considering Wind PowerIn order to analyze the influence of wind farm on the constructed CCTL-OPB,the influence mechanism of wind power accessing on the transient stability has been analyzed,during and after the system failure.The influence of the wind farm output changing can be avoided by describing the wind farm in the equivalent form.Furthermore,based on the extended equal area rule,the influence of doubly-fed induction generator on the system critical clearing time is quantitatively analyzed,and the rationality analysis of constructing the spatial CCT Limited Operation Point Boundary(CCTL-OPB)of power system parameters including wind power is given.Furthermore,based on the above CCT Limited Operation Point Boundary construction algorithm,the CCT Limited Operation Point Boundary considering wind farms is reconstructed.Then,the CCTL-OPB is converted into transient stability constraints,and the total transfer capability of the transmission section considering wind farms is calculated.Finally,the proposed transient stability constrained total transfer capability calculation method is verified and analyzed.