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Online Transient Stability Analysis And Control Of Power System Based On A Two-dimensional-one-order System

Posted on:2015-10-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:S ZhaoFull Text:PDF
GTID:1222330485991704Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
With the rapid development of the large scale AC/DC hybrid power system in China, the traditional transient stability analysis and control method based on off-line or SCADA/EMS data cannot satisfy the needs of the complex grid. Wide area measurement system(WAMS), however, can be considered as a new tool for power system online stability assessment and control. In this thesis, a stability analysis theory using two-dimensional-one-order adjoint power system(APS) is combined with the WAMS system, and then new online transient stability analysis and control methods are derived. Main work of the thesis is as follows:1) The theoretical foundation of APS is first reviewed, and its feasibility and the framework for the online transient stability analysis based on WAMS data are also discussed, which is the fundamental basis of the latter research. Numerical calculation method for APS using numerical differentiation formulas is proposed, which provides a practical technique for the thesis.2) A new criterion based on WAMS data and APS model to detect the transient stability with multi-swing for the complex and bulk power systems is proposed. In the criterion, minimum projection kinetic energy of the APS system is used to determine the critical point on the system stability boundary. And, curve fitting technique is adopted to accelerate the evaluation process. The proposed method only needs WAMS data and it does not rely on the network structure, system model and parameters, which cannot be determined exactly from the actual power grid. Furthermore, identification on the coherent generator groups and stable equilibrium point of the post-fault system can be avoided during the dectection process. Hence, the method is fast and highly accurate, and it is suitable for the online application.3) Adjoint concave dynamic system(ACDS) for the power system is proposed. A new stability criterion based on ACDS system for power system transient stability assessment is presented. And, the geometrical and topological characteristics of the APS’s curve are used for the criterion derivation. The ACDS system is an identity mapping of the APS system. The proposed method based on the ACDS system inherits all advantages of the APS system. Furthermore, it can avoid the detection failure caused by the nonlinear characteristic of the trajectory near the stability boundary, and the selection problem of the observation and prediction window for the proposed method are also improved. As a result, the proposed method is more flexible and effective for the instability detection.4) A partition-composition method is presented for the online transient stability evaluation in bulk power systems, and a hierarchical and partitioned framework is also designed. WAMS data of the subsystem can be used for the evaluation on its own transient stability. And the stability of the parent system can be determined only using few parameters uploaded from the subsystems based on the proposed method. Local and inter-area types of failures can also be determined. The proposed method is fast and suitable for bulk power system application, since only few parameters need to be exchanged between system monitoring and control centers.5) An online close-loop emergency control method for power systems is presented by using the ACDS model. In this method, a new stability index is given to rank the accelerating generators. Generators with large index value will be selected to trip. The tripping capacity can be calculated using the ACDS method. Coherent generator group identification and stability detection can be decoupled during the procedure, and control strategy can be generated without the offline data. Therefore, the given method can be utilized more effectively and practically for the online emergency control in the bulk grid.
Keywords/Search Tags:Power system, Wide area measurement system, Transient stability, Rotor angle stability, Transient energy function, Emergency control
PDF Full Text Request
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