Adaptive Control for a Class of Multi-Input Multi-Output Plants With Arbitrary Relative Degree

In this paper, a new adaptive output-feedback controller for a class of multi-input multi-output linear plant models with relative degree three or higher is developed. The adaptive controller includes a baseline design based on observers and parameter adaptation based on a modified closed-loop reference model. The overall design guarantees stability and tracking performance in the presence of large parametric uncertainties that are common in aircraft models with actuator dynamics. The requisite controller has a computational complexity that is an order of magnitude lower than that of a classical model reference adaptive controller. The proposed adaptive controller is evaluated using a model of a very flexible aircraft with second-order actuator dynamics and parametric uncertainties, and demonstrates stable command tracking behavior in scenarios that cause the failure of an linear quadratic regulator controller and an adaptive controller with a first-order actuator model.