Studies On Voltage Stability Of Power Systems Based On Bifurcation Theory And AUTO97

In this thesis, using AUTO97, a general continuation and bifurcation software, the problem of voltage stability in power system based on bifurcation theory is studied. The questions addressed in this work are: summarizing operative skill of AUTO97 and improving its capability; the effects of load characteristic, load location and network structure on voltage stability; the effect of generator model on voltage stability; multi-parameter bifurcation analysis on a typical power system, and so on. The main body of this thesis consists of the items as follows:(I) The operative skills and improvements of AUTO97With bifurcation theory applied in many fields, AUTO97, a continuation and bifurcation software for ordinary differential equations, has become an effective tool for applying bifurcation theory to analyze the problem of stability in nonlinear systems. The software by an example is introduced. AUTO97 was based on Unix operating system, which brings users inconvenience. By practice, detailed steps of the installation under Linux are presented. The way to set break point when operating AUTO97 is brought forward. The means how to link with Matlab for plotting three-dimensional figure is summarized.(II) Single-parameter bifurcation analysis of power system voltage stabilityA single-parameter bifurcation analysis is performed on a typical power system model. The results indicate that power voltage stability is influenced by load model, load location, network structure and generator model.1) The characteristic of constant current type load is more favorable for voltage stability than constant power type load. The characteristic of impedance type load does not affect the voltage stability. More realistic dynamic load models must be adopted in studying the mechanism of voltage stability.2) When the load is near to generators, the possibility of voltage collapse caused by system voltage oscillate and the power limit corresponding to saddle-node bifurcation will decrease. When the load is far away from generators, the increase of load will arouse system voltage oscillate.3) Without respect to the limit of excitation, the existence of excitation system increases the power transmission limit and avoids the occurrence Hopf bifurcation ofpower system.(III) Multi-parameter bifurcation analysis of power system voltage stabilityIn view of the existence of the controllable and uncontrollable parameters in real power systems and interaction of them in the dynamic process, multi-parameter bifurcation analysis on the same model is performed. The results show that the method by multi-parameter bifurcation analysis is superior to that by single-parameter in discovering the mechanism of voltage collapse and the effects of parameters on voltage stability.1) Without the limit of excitation, a higher reference Voltage and a bigger exciter-gain can not only increase the power transmission limit of the system and stability margin, but also decrease the possibility of voltage collapse caused by system voltage oscillate. There is a linear relation between the power transmission limit and reference voltage. There is a nonlinear relation between the power transmission limit and exciter-gain.2) The existence of the limit of excitation can reduce the stability margin of load. With the decrease of the limit of excitation, the power transmission limit corresponding to the saddle-node bifurcation point is decreasing. The reference voltage will be limited. The value of reference voltage should get to the greatest extent with satisfying the limit of excitation.3) There is a complementary relation between reference voltage and exciter-gain, thus adjusting reference voltage and exciter-gain properly can avoid Hopf bifurcation and increase the system's stability margin.