abstract
- This paper presents an adaptive nonsingular terminal sliding mode controller designed to converge with a constant rate, which restrains the control input to avoid peaks at the initial time. Thus, during the convergence time, the control law is based on a fixed-time extended state observer that provides a perturbation and uncertainty estimation, which is used to constrain such convergence. The sliding variable converges to a small region around the equilibrium at a desired time. On the other hand, a nonsingular terminal sliding mode is designed, guaranteeing practical finite-time state convergence and robustness for the control method. The stability analysis of the adaptive controller and the sliding surface is proven by means of Lyapunov and practical finite-time stability theories. Finally, a case study involving an unmanned surface vehicle subject to external disturbances and uncertainties is addressed, with an additional comparative analysis against alternative prescribed-time controllers. Numerical simulations and real-time experimental trials demonstrate the advantages and effectiveness of the proposed approach in a trajectory tracking scenario.