Curved Path Following Control for Fixed-wing Unmanned Aerial Vehicles with Control Constraint

The control inputs of a fixed-wing unmanned aerial vehicle (UAV) are affected by external environment, the largest mechanical limits and energy limits. It is essential to consider the control constraints for the curved path following problem when the curvature of the desired path is continuing-changed. This paper presents two approaches to address the curved path following problem of fixed-wing UAVs subject to wind and we explicitly account for the control constraints. First, a proper state feedback controller is developed that is based on the tracking error equation defined in the Frenet-Serret frame to confirm that there is a control Lyapunov function (CLF) for input constrained case. Second, a stabilizing guidance law with control damping based on the designed CLF, which satisfies the small control property, is implemented to ensure the global asymptotic stability of the fixed-wing UAV curved path following subject to wind. Meanwhile, a control scheme with the nested saturation (NS) theory for curved path following is also developed with proven stability. The simulation results are presented to illustrate the effectiveness and high tracking performances of the proposed control strategies.