Study On Very Low-frequency Oscillation Suppression Of Generator Excitation Control

With the implementation of the Three Gorges Project and the project of transmitting electric power from west to east, a large scale power grid is forming. How to improve stability of the grid is an important problem. Excitation controller is a necessary part of the generator set. It's helpful for improving stability of the power grid. Large-scale power systems in infirm interconnections which inhere weak natural damping sometimes bring a low frequency self-oscillation phenomenon. The interconnection of national power grids in China brings new issues into power system stability and control, especially very low-frequency oscillation(0.13Hz) .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 biter 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 occur, 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. 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 researched the reasons of negative-damping, using theory of small signal and synchronous generator. The reasons that influence very low-frequency oscillation and the inhibiting effect of PSS were proved by experiment in the dynamic simulation laboratory. In order to deeply research the inhibiting effect of the excitation control strategy such as AVR, AVR+PSS1A, AVR+PSS2A, AVR+PSS2B, LOEC, frequency-domain analysis method and time-domain analysis method were combined together. Two characteristic point, one is a typical very low-frequency oscillation (0.13Hz) point and the other is a typical low frequency oscillation point (0.97Hz) were analyzed.The quick constringency of low frequency oscillation of generator which realized by LOEC excitation stability strategy is of very positive significance for the safe operation of power system. This excitation stability strategy inhibits very low-frequency oscillation effectively, 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.