Abstract
In this paper, we investigate the problem of robust altitude stabilization for the vertical take-off and landing (VTOL) of an unmanned aerial vehicle in the presence of external disturbances (e.g. wind gusts), payload variations, and noisy measurements. The design of the controller is simple; it is based on the minimization of the one-step-ahead predicted position errors. The stability analysis of the closed loop in the presence of external disturbances is presented. The analysis results prove that the tracking errors of attitude, take-off, hovering, and landing are uniformly bounded. Since the proposed control algorithm will be employed for goods delivery by drones, the robustness of this algorithm against low-frequency disturbances and payload variations is a major objective. To this end, integral action is included in the altitude loop to eliminate the induced steady-state error and to drop off the payload in the desired position successfully. Furthermore, the controller is given in the closed form to facilitate its implementation onboard to increase the autonomy of the flight. The numerical simulations are provided to show the effectiveness of the proposed algorithm.