H_infinity Loop-Shaping Control of Aerospace Systems

Loop-Shaping design with H_infinity controller synthesis plays a role of primary importance for the synthesis of robust multi-variable controllers. However, a typical difficulty is that the designer has to develop considerable expertise in this matter before obtaining good results. In fact, the choice of the weighing matrices, that are at the heart of the loop-shaping design, is not an easy issue. The aim of the work described in this dissertation is to improve the well known H_infinity loop-shaping approach, by simplifying the shaping procedure and by extending its range of effectiveness, through some useful additions helping the designer in the controller synthesis. The first major improvement consists in the definition of a scaling method aiming to minimize the condition number of the plant. This simplifies the choice of weights and increases the closed-loop robustness. A second important addition is the development of a design procedure helping the designer in the selection of non-diagonal weights, which seems the best solution to overcome difficulties related to plants with highly coupled dynamics. A Matlab software package has been created, which implements the proposed design procedures and assists the designer by simplifying the shaping activity and reducing his/her amount of work. The exposed design methodologies are validated through some case studies, where typical problems of flight control system design are dealt with. These applications are illustrated with the aid of a Matlab/Simulink linearized model of an aircraft.