Robust Observer-Based Dynamic Sliding Mode Controller for a Quadrotor UAV

In this paper, a novel robust backstepping-based approach combined with sliding mode control is proposed for trajectory tracking of a quadrotor UAV subject to external disturbances and parameter uncertainties associated with the presence of aerodynamic forces and possible wind force. To enhance robustness, a nonlinear disturbance observer (NDO) is employed alongside the controller. A sliding surface is introduced, which shares intermediate control goals with a conventional backstepping scheme. The closed-loop system comprising the sliding mode and backstepping controllers is finally combined with the NDO to track the desired position and attitude trajectories. Good tracking is achieved in the closed loop if the controller and observer gains are selected correctly. The system performance exhibits much better robustness than the existing backstepping control methods, which are not equipped with nonlinear disturbance estimators. The simulation results are confirmed in terms of real laboratory experiments. Prior to the implementation of the control method, the real system has been identified and calibrated.