Probabilistic Transient Stability Evaluation Of Flexible Composite Power Systems

This dissertation is supported by National Natural Science Foundation of China (50977094) and Scientific Research Foundation of Stage Key Lab. of Power Transmission Equipment and System Security (2007DA10512709103).The rigid restriction of power system can be bated by flexible composite elements, consequently the static and dynamic stability can be improved. In this paper, small signal stability analysis and time domain simulation of multi-machines system have been analyzed by PSAT(Power System Analysis Toolbox);Also a simulation junction between new flexible generator-ASG(Asynchronized Synchronous Generator)and PSAT has been established; Based on Monte Carlo method, the probability quantitative evaluations of impacts of ASG and TCSC(Thyristor Controlled Series Compensator) to system transient stability have been given.TCSC is a new type of FACTS, its application is very comprehensive. The equivalent impedance of TCSC could be changed by changing impedance of TCSC continuously, thus system oscillation could be damped and system transient stability could be improved. Most of existing researches are focus on controlling strategy of TCSC. The general analysis about impact of TCSC upon system transient stability is very little. In this paper, the working principle, running mode and effects to system transient stability of constant- power-controlled TCSC have been studied and simulated. Also, the impact of TCSC to multi-machine system transient stability has been calculated.Asynchronized generator is a new kind of flexible machine with controlled rotor MMF to rotor axis. Because of this flexibility, ASG has a lot of preferable features compared to conventional system generator. It is very difficult to use existing ASG model for PSAT simulation directly, so in order to achieve an organic link between ASG and PSAT, a new ASG module has been built by UDM (user designed model) of PSAT. The single-machine infinite bus system and 4-machines 9 buses system are used to test the validation of the new ASG module.Conventional stability analysis is only aim at some worst cases, but most of the factors that can affect system running are stochastic, so probability transient stability evaluation is more objective. There are a lot of random factors that can affect system running, in this paper, load, fault location, fault types and clearing time have been considered. Probability transient stability evaluations on conventional system, systems containing ASG and system containing TCSC have been given based on the WECC3-machines 9-buses system prototype. In allusion to different fault elements, the conditional probability of transient instability has been calculated; the losing of transient stability probability has been calculated also, it is used to reflect whether there is a flexible element in the system.