Optimal and sub-optimal loop shaping in quantitative feedback theory
Abstract
Within the scope of control of uncertain systems, the problem of performance robustness, especially in the face of parametric uncertainty, has been recognized as a predominant issue of engineering significance in many design applications. Quantitative Feedback Theory (QFT), a frequency response-based method introduced by Horowitz, has been shown advantageous in many cases where performance specifications for such systems, in terms of hard constraints on closed loop response, are to be met. One of the primary drawbacks of the method has been the lack of a closed-form procedure for the synthesis of optimal controllers. The focus of this thesis is upon a fixed-structure, parametric optimization formulation of the controller design problem. Following a background study and a detailed problem formulation, features and implications of a nonlinear programming solution are discussed. The method is demonstrated by application to a lateral autopilot design for an uncertain C-135 aircraft model, both to the traditional QFT design specifications as well as to a relaxed, sensitivity-based criterion. The advantage of the latter formulation is a greater degree of mathematical commonality with competing frequency domain methods, thus laying the groundwork for future benchmark studies in control design.
Degree
Ph.D.
Advisors
Nwokah, Purdue University.
Subject Area
Mechanical engineering|Aerospace materials|Electrical engineering
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