Nonlinear robust backstepping controller for attitude control of a rotary wing unmanned aerial vehicle

This paper presents a nonlinear control scheme to control the attitude of a small-scale rotary wing unmanned aerial vehicle (RUAV) in the presence of external disturbances. The proposed attitude controller is designed in such a way that it is robust to external disturbances. To prove the convergence of the attitude tacking error to zero, i.e., the actual attitude of the closed-loop system to reference attitude of RUAV, a control Lyapunov function (CLF) is formulated in every step of the design procedure which is ensured through the negative definiteness of the derivative of CLF. Finally, the performance of the proposed controller is tested using a high-fidelity simulation model by considering external wind gusts into the system. Simulation results illustrate the robustness of the proposed controller over an existing controller in terms of rejecting external disturbances.