Research On A New Stability Strategy Of Excitation Control

The complexity of power systems is continually increasing because of the growth in interconnections and use of new technologies. At the same time, financial and regulatory constraints have forced utilities to operate the systems nearly at stability limits. These factors have created new types of stability problems. Large-scale power systems in infirm interconnections which inhere weak natural damping sometimes bring a low frequency self-oscillation phenomenon. In addition, popularizations of fast automatic voltage regulator which show itself negative-damping even more worsen this situation. Rising swing of the low frequency self- oscillation will destroy system stability and cause enormous economic losses and calamitous consequence .There have been lots of bitter lessons in the world.It is very important to strengthen power net framework for avoiding low frequency self-oscillation. But along with the development and variation of power system, a new infirm interconnection of power system may be occured, it is not only of diseconomy but also impossible to avoid weak damping of system only by enhancing configuration of power system. One of the most efficient and economic way among those methods to improve stability of generators, which has been acknowledged generally, is to upgrade the performance of excitation device. But such performance of the traditional excitation devices as robustness,fast response and effectiveness are still not very well resolved.The main subject of this dissertation based on the China National key project is the research on the control mode of excitation system, which is a subsection of Sanxia Electromechanical Equipment Research. In this paper the origination of the problem of power system stability and its principal mathematic analysis method are introduced. Then the effect on the stability of power system by excitation system is discussed in detail. The paper analysed the reasons of negative-damping, using theory of small signal and synchronous generator, Through the in depth study of F. D. Demello dynamic model of electromechanical transition and synchronous generator theory, focusing on the simpleness reliability and robustness, a new excitation devicecontrol strategy that can eliminate the negative-damping phenomenon is proposed. By the static stability analysis and dynamic simulation analysis, this additional excitation control can increase the system damping and improve system stability with very good robustness. The engineering realization scheme of this control strategy is described in this thesis.The quick constringency of low frequency oscillation of generator which realized by new excitation stability strategy is of very positive significance for the safe operation of power system. Thermal accumulation of generator will be cut down through reducing swing times of generator, and at the same time, the stability of power system is improved. The subject is of potential both theoretically and practically. So it is necessary to continue the further study and evaluate on its application both theoretically and practically.