| With the development of modern power system, voltage stability has been becoming a concerned problem. Many methods for voltage stability analysis are based on deterministic method. However, there are uncertainties such as measurement errors, forecast inaccuracy and outages of system elements in power systems. To carry out deterministic voltage stability analysis for every possible or probable combination is impractical because of an extremely large computational requirement. In this thesis, probabilistic methods are used to analyze and improve voltage stability considering the random variations of loads and load parameters.;Firstly, voltage stability is studied as a static problem. Probabilistic power flow is combined with point of collapse method to determine the probabilistic characteristic of stability margin under the load random variation. Then maximum entropy is adopted to determine the distribution of stability margin. The effect of load uncertainty on the stability margin is also analyzed.;After static voltage stability analysis, probabilistic eigenvalue is used to analyze the voltage stability considering load random variation and load parameter random variation respectively. In this study, the loads and load parameters are normal distribution and the probabilistic eigenvalue will be close to normal distribution. However, the computed stability margin distribution is irregular. Therefore, two stability margin indices are employed to quantify the degree of stability. The effects of load level uncertainties and load parameter uncertainties are examined via these two indices as well as the margin distributions.;Finally, power system voltage stabilizer (PSVS) is adopted to improve voltage stability of power system by considering the load level uncertainty. The PSVS output will be injected to generator exciter and modal participation factor is used to locate the most appropriate generator. The PSVS input signal should be bus voltage; modal coefficient and probabilistic sensitivity indices are employed to select the most appropriate bus. The settings of PSVS parameters are then adjusted by the Quasi-Newton method. Subsequently, voltage stability of power system under wide range of operation can be enhanced by the present systematic PSVS design. |
