Fast Terminal Sliding Mode Control for Quadrotor Unmanned Aerial Vehicle with Actuator Saturation

We propose a nonsingular fast terminal sliding mode control method for quadrotor unmanned aerial vehicle based on multi-loop control structure, which improves the convergence rate and solves the singular problem in the traditional terminal sliding mode control. Many problems exist in practical applications of quadrotor unmanned aerial vehicle, such as model uncertainties, external disturbances, and actuator saturation. First, considering the model uncertainties and external disturbances in the position and the attitude loops, we design a nonsingular fast terminal sliding mode controller with the use of the adaptive method to handle uncertainties and disturbances. Then, we consider the actuator saturation problem in the rotate speed loop. The saturation is treated as additive disturbance and is estimated by a sliding mode disturbance observer. Finally, we design a sliding mode controller based on the disturbance observer to achieve convergence within a finite time. The stability of the closed-loop system is proven by the Lyapunov method. Simulation results show that the proposed control scheme can guarantee fast error convergence regardless of model uncertainties, external disturbances, and actuator saturation.