Research On Power System Transient Stability Based On Critial Machine Pair

As the network scale expanded and blackout events around the world, transientstability analysis and emergency control are paid more and more attention. Althoughresearch has made significant effect, it is still faced with many difficulties inapplication. In recent years, transient stability analysis based on WAMS (Wide AreaMeasurement System), usually requires all generators information. Due to theexpensive costs, it is impossible to install PMU (Phasor Measurement Unit) devicein all generator buses. The PMU incomplete configuration, constrains the methodswhen applied to the observability and controllability in a certain extent. Even if allthe generator buses are installed the PMU, it is necessary to be used all? Whetherthere are methods which have weak need to the PMU information or just need somekey buses information to meet the analysis and control? Starting from thiscontradiction, critical machine pair, being composed of critical machine andnon-critical machine, reflecting the stability, is as research objects. This paperresearches detailedly on power system transient stability analysis method, limitparameter, emergency control strategy.For the demonstration of critical machine pair theoretical correctness, the paperderives the consistency of the EAC (Equal Area Criterion) and the transient energyfunction method in judging system stability, discusses that critical machine pairinformation may reflect on stability of the whole system. Based on this, the paperproves that EAC can be used to critical machine pair to analysis the stability ofsystem, lay the foundation for simple and practical method of power systemtransient stability analysis and control.For obtaining multi-machine power system transient stability rapid assessmentmethod based on critical machine pair and EAC, based on critical machine pairPMU data within a short time after failure, the paper predicts power-angle curve bycurve fitting and judges stability in real time by EAC. Also the paper gives systemstability index and error analysis of the method. Research shows that the methoddoes not need to identify the critical cluster, less information required, significantlyweaken the PMU configuration requirements in real time applications. Simulationresults show high accuracy, validate correctness of the method.Critical machine pair power angle curves can be fitted by sine curve normally,weather it is suitable when strong time-varying factors appear is an issue problem.For the power angle sine fitting curve, the paper analyzes the strong time-varyingfactors effects on transient stability, propose time-varying factors strong or weak indicators based on model or not rely on. The paper analyzes distribution of strongtime-varying factors, further points out the sinusoidal function power-angle curvesfitness. Based on this, the paper proposes transient stability identification methodand stability index calculation method considering strong time-varying factors.Precision is very high, but the calculation speed has dropped, online analysis isrecommended.CCT (Critical Clearing Time) is commonly used in power system transientstability assessment.This paper proposes the calculation of CCT by critical machinepair information. Usually2~3iterations can converge to the actual value. Insimulation process, it only needs two machines information, the complex dataprocess is eliminated, especially for large systems, this effect will be morepronounced. Further more, improved CCT calculation method is proposed,calculation time significantly reduces than the time domain simulation and theiterative method based on all units.Cutting machine and load-shedding calculations by energy function stabilitymargin sensitivity was widely recognized, but the whole system stability marginsensitivity does not reflect adjustment of each instability units. Based on this,this paper proposes cutting machine and load shedding control algorithm based oncritical machine pair stability sensitivity. Derives critical machine pair stabilityindex sensitivity expression, and gives the cutting machine and load-sheddingposition and number. Further more, combined with non-real-time transient stabilityanalysis method based on trajectories, the paper put forward the―online decisions,real-time match‖control strategy; combined With real-time transient stabilityanalysis methods, the papers put forward the―real-time decision, real-time match‖control strategy. Eventually a comprehensive closed-loop emergency control systemis formed, can achieve on-line monitoring and control for power system.