Robust control techniques for aerospace vehicles

The research work presented in this thesis deals with flight control problems. Based on robust control techniques such as H _∞ control and μ-synthesis, we develop control laws that are efficient in reducing gust loads on flexible aircraft. Uncertainty models for flexible aircraft are proposed and shown to be well adapted for robust control design, while tightly covering unknown but bounded variations of flexible mode parameters. One of the models presented introduces a new complex-rational controller design methodology that takes advantage of the uncertain plant structure and achieves good performance criteria. Other uncertainty models are presented for the first time for the purpose of closed-loop reduction of flexible models. We propose a new model/controller order reduction method for flexible aircraft preserving robust performance in closed loop. Two case studies of complex aircraft are presented with the objective of full flight envelope control. Solutions for scheduled control laws are given to maintain performance objectives along the entire flight envelope. We adapt to our complex aircraft case study known gain scheduling techniques such as observer-form controller scheduling, and we propose new gain scheduling techniques, including a robust performance blending/interpolation design, an optimal multi-switching methodology and a scheduled-partitioned controller.