Flemming, Ronald J.2017-08-182017-08-181991-10October 19http://hdl.handle.net/10388/8027In recent years, intermachine oscillations in a multimachine plant have received particular attention from power system engineers due to the undesirable effects of these oscillations on the system, and also due to the fact that the individual stabilizers now in use are not effective in damping out all modes of oscillation. A multivariable stabilizer can be advantageous to stabilize the dynamic performance of a multimachine plant in which all parallelly connected units act simultaneously. In this thesis, three kinds of novel stabilizers for a multimachine plant are proposed. The first one, named the Optimal Multivariable Stabilizer (OMS), is based on linear optimal control theory and the Generalized Heffron-Phillips model of a multimachine plant. The second design, named the Optimal Variable Structure Stabilizer (OVSS), is based on a combination of variable structure control theory and linear optimal control theory and also the Generalized Heffron-Phillips model. The third design uses the concept of variable structure control to improve conventional power system stabilizers (PSS) and is named the Improved Power System Stabilizers (lPSS). Guidelines for the setting of these three kinds of stabilizers are presented in this thesis. Nonlinear simulation results in small and large disturbance cases are reported to demonstrate the great capability of these stabilizers to damp out the intermachine oscillations.Thesis