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Abstract
The first contribution of this dissertation is the case studies for capturing the development of different types of dynamic voltage instability, in both the short- and long-term, caused by the dynamics of different power system devices, especially induction machines. In addition, it investigates how the changing nature of systems and their dynamic behaviours cause critical issues that limit the large-scale integration of wind generators and flexible AC transmission system (FACTS) devices. A second and unique contribution of this thesis is the presentation of a method to bound unmodelled nonlinear dynamics and to design excitation control for the enhancement of large-disturbance voltage stability in power systems with significant induction motor loads. A new technique is developed which captures the full nonlinearity of systems in the region of interest. The nonlinear power system model is reformulated with a linear and a nonlinear term. The nonlinear term is the Cauchy remainder in the Taylor series expansion and in this thesis its bound is used in robust control design. This dissertation also presents an algorithm for the design of a decentralised robust controller for static synchronous compensators (STATCOMs) which results in a significant increase in the available dynamic transfer capability of a power system in the presence of fixed-speed induction generators (FSIGs). Another significant contribution of this research is the design of robust controllers which augment the low-voltage ride-through capability of FSIGs during severe disturbances. Control algorithms, using both structured and unstructured uncertainty representations, are developed for the stabilisation of faulted systems under different operating conditions. The performance of the proposed control schemes fulfils the criteria for robust stability and performance, and produces adequate stability margins for a range of test cases. The effectiveness of the suggested control strategies are validated by detailed simulations with complete nonlinear model of the devices. The performances of the designed controllers are also compared with those of conventional controllers. Simulation results show that both the dynamic voltage stability and the transient stability of a power system can be improved by the use of the robust control methods presented in this thesis.