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.