| Power system long term dynamic stability studies and simulations are associated with the dynamic response of power systems to severe disturbances. Severe system disturbances result in large excursions of voltage, frequency, and power flows which may invoke the action of slow processes such as boilers and energy supply systems not modeled in conventional transient stability studies. There is limited experience and literature on the nature and scope of long term dynamic stability studies and analytical tools for studying these aspects of power system dynamics are still evolving, particularly in the simulation of slow as well as fast dynamics by long term stability programs.; This thesis addresses two aspects of power system long term dynamics and stability simulations: system components modeling and frequency effects analysis. In the system modeling, singular perturbation techniques are used to reformulate dynamic component full models. These reformulated models are called singularly perturbed models or singular perturbation models. The advantages of the singular perturbation models are that they retain the identity of the state variables and model the interaction between the fast and slow dynamics. In the thesis, the singularly perturbed models for generators, fast exciters, power system stabilizers (PSS), governors and turbines, induction motors and static var compensators (SVC) are developed, implemented and tested in a two-area, four-machine system as well as a large practical power system. The dynamic performance of the singularly perturbed models is compared with the full models as well as the simple models which completely neglect fast transients during simulations. The benefits are seen from the singularly perturbed models in terms of computational accuracy and efficiency. The models derived in this thesis are also verified using eigenvalue techniques and, once again, they show consistent and satisfactory results. The research in this thesis provides a basis for the future implementation of the singularly perturbed models in a production grade simulation program.; Since one of the characteristics in the long term stability simulation is that the system frequency may significantly deviate from its nominal value due to the severity of the disturbances, in addition to modeling the power system dynamic components using singular perturbation techniques, this thesis also addresses the effects of frequency variations on system components and their dynamic response, with emphasis being placed on such devices as generators/governors, induction motors and SVCs which are sensitive to frequency changes. From this analysis it is seen that the singularly perturbed models can effectively account for such frequency changes in long term stability simulations. This further proves that the singular perturbation technique is an efficient method for long term dynamic stability simulations. |
