Lateral control for UAVs using sliding mode technique

This paper presents sliding mode based lateral control for UAVs using a nonlinear sliding approach. The control is shown to perform well in different flight conditions including straight and turning flight and can recover gracefully from large track errors. Saturation constraints on the control input are met through the nonlinear sliding surface, while maintaining high performance for small track errors. Stability of the nonlinear sliding surface is proved using an appropriate Lyapunov function. The main contribution of this work is to develop a robust lateral control scheme that uses readily available sensor information and keeps the track error as small as possible without violating control constraints. In the proposed scheme the only information used in the control law is the lateral track error and the heading error angle. No information is required about the desired path/mission, which therefore can be changed online during runtime. This scheme is implemented on a high fidelity nonlinear 6-degrees-of-freedom (6-dof) simulation and different scenarios are simulated with large and small track errors in windy and calm conditions. Simulation results illustrate the robustness of the proposed scheme for straight and turning flight, in the presence of disturbances, both for large and small track errors. Furthermore it is shown that the saturation limits of the control input are not exceeded in all cases.