Researches On Voltage Stability In Power System

This dissertation conducts research works on the mechanisms, modeling and analysis method of voltage stability. The relationship of voltage stability and angle stability is discussed thoroughly. The general framework of real-time voltage stability monitoring and controlling is also presented. The main function of this framework is implemented in a real system.The current definition of voltage stability can't distinguish voltage stability problem from load stability and angle stability problem clearly. As the reault, the angle stability model that includes static or dynamic load character can be used to study transient voltage stability problem. Transient voltage stability can be defined by means of Singularity Induced Bifurcation (SIB); this offers an approach of transient voltage stability analysis. The possible methods to unite voltage stability and angle stability analysis are energy function method and bifurcation analysis method.Under the light of energy function method, angle instability and voltage instability can be thought as different unstable mode, and be distinguished from each other by characteristic of UEP. The possible unstable mode is influenced by load model, load location, network structure and system operation manner. The lower part of PV curve contains abundant information about UEP bifurcating as power changes.The SIB of Differential-Algebra Equation (DAE) can be interpreted as one mechanism of transient voltage unstable or voltage collapse, and this mechanism is illustrated under multi-machine system. Moreover, the algorithm for search SIB point under multi-machine system is proposed. The study of DAE model and its singularity-perturbed model shows that they are different in essence. Inconsistency may exist under small signal stability analysis of UEPs. Structure preserved energy function method uses DAE model in actual application, this may lead to SIB and make the result pessimism with respect to simulation method. Besides, the concepts, such as SIB and multiple energy function sheets, are explained by picture.The relationship among induction motor stability, system voltage stability, and angle stability is studied detaily by simulation method. The mechanism that induction motor losing stability can lead to voltage stability is confirmed by the analysis results of typical system and multi-machine system.The general framework of voltage stability real-time monitoring and controlling is expounded, and one real system application case of this framework is narrated. The practical performances of common used static voltage stability analysis algorithm are briefly discussed.