Qihua Zhao

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


In this thesis, robust damping control design techniques that improve the small disturbance stability of power systems are presented. To ensure power system stability, the controllers used in power systems have to be "robust", that is, they must be able to provide sufficient damping to the oscillatory modes under all possible operating conditions. A frequency-domain robust control design based on the {dollar}H\sb{lcub}\infty{rcub}{dollar} optimization technique is used in this thesis to design the damping controllers. The model variations caused by the operating condition changes are treated as model uncertainties, and considered explicitly at the controller design stage.;A robust multivariable controller is designed for an excitation system using the standard {dollar}H\sb{lcub}\infty{rcub}{dollar} mixed-sensitivity formulation. To simplify the design process, a new damping control formulation based on the {dollar}H\sb{lcub}\infty{rcub}{dollar} optimization is proposed, and is applied to the damping control design for a two-machine system with an SVC. Damping controller devices using other FACTS devices such as the TCSC and the UPFC are also investigated in a four-machine two-area system. Nonlinear time domain simulations are performed, for all cases except the UPFC, to verify the damping contribution of the controllers and the robustness of the dosed-loop systems against operating condition variations. Some important issues, such as the derivation of the linearized power system model, the accommodation of model uncertainties in the context of power systems, the selection of the weighting functions, the treatment of pole-zero cancellation, and the selection of feedback signals, are addressed in the thesis.;It is concluded that the proposed new formulation can indeed simplify the selection of the weighting functions and make the controller design process more transparent to the designer. The controllers designed using this new formulation can provide positive damping to the system under all possible operating conditions. It is also demonstrated that the FACTS devices considered in this thesis are able to provide additional damping to the system oscillation modes in addition to their primary functions.



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