Constrained Control of UAVs Using Adaptive Anti-windup Compensation and Reference Governors

Gliders can climb to substantial altitudes without employing any on-board energy resources but using proper piloting skills to utilize rising air currents called thermals. Recent experiments on small Unmanned Aerial Vehicles (UAVs) indicate a significant potential to increase both the flight velocity and the range of gliders by means of such maneuvers. In these experiments the velocity to approach a thermal has been recognized as a critical performance factor, and is chosen as the controlled variable. Accurate longitudinal controllers are required to track the optimal flight trajectories generated using path planning algorithms. These controllers are challenged by the presence of uncertain and time-varying aircraft dynamics, gust disturbances, and control actuator limitations. With a broader objective of utilizing thermals to optimize the flight performance of autonomous UAVs, we focus on handling elevator constraints imposed on an uncertain aircraft model whose parameters are estimated online. We implement an adaptive control design with two different add-on schemes to address both the actuator magnitude and rate constraints. The first approach is based on an anti-windup compensator, whereas the second one uses the reference governor. The two constrained control methodologies are compared through simulation results.