ABSTRACT Title of dissertation: PROBLEMS IN SELECTIVE MODAL ANALYSIS AND CONTROL

In this dissertation, we develop monitoring and control systems for improv-ing the performance of systems that are required to operate at the edge of their stability envelopes. The concept of modal participation factors, which is an essen-tial construct in the theory of Selective Modal Analysis, is used extensively in this work. The basic definition of modal participation factors that was originally given for unforced linear time-invariant systems is revisited, and related notions of out-put participation factors and input-to-output participation factors are introduced, studied and applied to models of electrical power systems. A signal-based approach for real-time detection of impending instability in nonlinear systems is considered. The main idea pursued involves using a small ad-ditive white Gaussian noise as a probe signal and monitoring the spectral density of one or more measured states or outputs for certain signatures of impending in-stability. Input-to-state and input-to-output participation factors are used as tools to aid in selection of locations for probe inputs and states or outputs to be mon-itored, respectively. Since these participation factors are model-based, the wor