Robust optimal control for attitude tracking of hexarotor UAVs: Switching robust compensator approach

This paper proposes a robust optimal control design for attitude tracking of hexarotor unmanned aerial vehicles (UAVs) in varying operating conditions subject to external disturbances under the presence of parametric uncertainties, nonlinear dynamics, and coupling. All these uncertainties are considered as equivalent disturbance in this paper. The proposed attitude controller is designed for pitch, roll, and yaw subsystems and it consists of a nominal optimal controller and switching robust compensator. The nominal optimal controller is based on linear quadratic regulator (LQR) control approach to achieve good tracking performance in nominal condition. The switching robust compensator is added in order to improve the attitude tracking performance due to the presence of equivalent disturbance where the amount of equivalent disturbance is changing dynamically. The simulation results prove that the switching robust compensator has ability to maintain the robustness in small and large amount of equivalent disturbance. It also prove that the attitude tracking errors are bounded in specified boundaries.