Studies On The Effects Of Generator And Load Models On Voltage Stability By Bifurcation Theory

In this thesis, studies are made on the problem of voltage stability in power system based on bifurcation theory and numeric simulation method using AUTO97, a general continuation and bifurcation software. The questions addressed in this work are: analyzing and summarizing the effects of main component characteristics on voltage stability; the effects of three typical load models on voltage stability; the effects of generator models on the voltage stability of a typical power system and so on. The main body of this thesis consists of the items as follows:( â…  ) The effects of main component characteristics on voltage stabilityThe strong nonlinearity of power system and components' dynamic characteristics are the source leading to voltage instability. Based on the present achievements, this dissertation discusses and summarizes the effects of main component characteristics such as load models, OLTC, generator models and SVC on voltage stability.(â…¡) The effects of load models on voltage stabilityThe main analysis objects in this thesis are generic static load model, GNLD integrated load model and WALVE integrated load model. The analysis results as follows:1. The characteristic of constant current type load is more favorable for voltage stability than constant power type load. The characteristic of constant impedance type load doesn't affect the voltage stability.2. In the areas where there are more constant temperature type loads or loads controlled by temperature, the realistic loads models such as GNLD integrated load model should be adopted, because the voltage stability is more influenced by their power comeback characteristic.3. As far as the voltage stability is concerned, the WALVE integrated loadmodel is more complex than the generic static load model because of the existence of Hopf bifurcation in the power system. Therefore, the more realistic dynamic load models must be adopted in studying the mechanism of voltage stability.(Ill) The effects of generator models on voltage stabilityThe study is made on a typical power system. The analysis results as follows:1. If the generator model employed is four order or six order model which thinks of g winding, the system will undergo supercritical Hopf bifurcation; if the generator model employed is 3 order or 5 order model which doesn't think of g winding, the system will undergo subcritical Hopf bifurcation. No matter what characteristic of the Hopf bifurcation the system undergoes, it will appear voltage oscillation and lose its stability gradually via period doubling bifurcation leading to chaos or torus bifurcation leading to torus cracking.2. The analysis result is more optimistic when the generator model employed is five order or six order which thinks of the subtransient of the generator than three order or four order which only thinks of the transient of the generator. Then, the dynamic stability range of the system will be increased accordingly.3. It isn't appropriate to employ the two order generator model in the dynamic voltage stability analysis because it approximatively thinks of the excitation system and the result isn't precise.