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UBC Theses and Dissertations

Multi-mode stabilization of torsional oscillations in single and multi-machine systems using excitation control Yan, Andrew


Subsynchronous Resonance (SSR) phenomena in a thermal-electric power system with series-capacitor-compensated transmission lines may cause damaging torsional oscillations in the shaft of the turbine-generator. This thesis deals with a wide-range multi-mode stabilization of single-machine and multi-machine SSR systems using output feedback excitation control. Chapter 1 summarizes the SSR countermeasures to date. Chapter 2 presents a unified electro-mechanical model for SSR studies, illustrates the torsional interaction between the electrical and mechanical systems, and demonstrates that multi-mass representation of the turbine-generator must be used for SSR studies. For the control design, a reduced order model is desirable. For the model reduction, modal analysis is applied to identify the excitable torsional modes, and a mass-spring equivalencing technique to retain only the unstable modes is developed in Chapter 3. Using the reduced order one: machine models, linear optimal excitation controls are designed in Chapter 4. The controls are further simplified by examining the eigenvalue sensitivity, and the results are tested on the linear and nonlinear full models. In Chapter 5, the stabilization technique is further extended and applied to a two-machine system and a three-4nachine system. The stabilizers still can be designed one machine at a time using a one-machine equivalent for each machine by retaining only the path with the strongest interacting current and the critical electrical resonance frequency as seen by the machine. To coordinate all controllers for the entire system, an iterative process is developed. The controllers thus designed are tested on linear and nonlinear full models. From both eigenvalue analysis and nonlinear dynamic performance tests of the one-machine, two-machine, and three-machine systems, a conclusion is drawn in Chapter 6 that the excitation controls thus designed by the methods developed in this thesis can effectively stabilize single-machine and multi-machine SSR, systems over a wide range of capacitor compensation.

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