Robust control of flexible aircraft with uncertainty

The objective of this research is to develop robust flight control designs to control the dynamics of a flexible aircraft. The flight control design needs to address two problems: model reduction of a higher-order system describing the dynamics of a flexible aircraft to a computationally more efficient lower-order system and the design of a robust controller for a system with uncertainties. Three model reduction methods are investigated: the Schur method, the singular perturbation method and the model reduction method based on the norm ranks of the structural modes. These model reduction methods are applied to several flexible aircraft dynamical models to generate the so-called “reduced-order models.” These reduced-order models are then employed in robust controller design. The applicability of these reduced-order models is evaluated by comparing them with the full-order model using simulations. In the robust controller design, the unstructured uncertainty due to model reduction error as well as the structured parametric uncertainty due to system parametric variations is considered. Three H_∞ control designs are investigated. In addition, the nonlinearity of the actuator is considered to ensure the control robustness of the closed-loop system.