Attitude Tracking Control for a Quadrotor UAV Using an Adaptive Chattering-Free SMC

This paper addresses an adaptive sliding mode nonlinear controller design for the attitude tracking of an autonomous quadrotor unmanned aerial vehicle (UAV). To overcome the chattering phenomenon in the controller signals, the proposed design is realized by considering the integral of the controller signal. In addition, Lyapunov-based estimations are employed, instead of bounded values of nonlinear functions and their derivatives in the controller design. Thus, the nonlinear functions that impose a computational burden on the controller signal in the classical nonlinear control method are used with their upper bounds estimated in the design. Furthermore, a singularity-free sliding mode approach is proposed to avoid the potential singularities in the adaptation mechanism. The asymptotic stability of the closed-loop dynamics is proved in the sense of Lyapunov theory. The effectiveness of the proposed control method is verified by comparative numerical simulations of the quadrotor UAV, demonstrating the robustness of the controller against external disturbances, model uncertainties, and partial actuator faults.