Finite-time adaptive sliding mode trajectory tracking control of ship with input saturation

A finite-time adaptive sliding mode ship trajectory tracking control strategy is designed to address the problems of unknown external disturbances, model uncertainties and input saturation of underactuated ship during navigation. By using neural networks to approximate the model uncertainties and using adaptive laws to estimate upper bound on the sum of the unknown disturbances and the neural network approximation errors. The “differential explosion” problem is solved by using dynamic surface technique, and design the controller with the finite-time convergence theory. Finally, the theoretical analysis is carried out by Lyapunov method, which proves that all signals of the closed-loop system are bounded. The simulation results show that the proposed control scheme is able to achieve trajectory tracking for underactuated ship regardless of whether input constraints are considered or not, and has satisfactory robustness in the face of unknown external time-varying disturbances and model uncertainties. The research done can provide effective reference for ship trajectory tracking control and has certain theoretical guidance significance. •For the problems of unknown external disturbances, the existence of model uncertainties in the ship, and the “differential explosion” problem, the RBF neural networks are used to estimate the uncertainties, and then the adaptive laws are used to estimate the upper bound of the sum of the external disturbances and the neural network approximation errors, and finally the dynamic surface technique is used to solve the “differential explosion” problem.•To address the problem of slow convergence, the design of the controller will be done in conjunction with the theory of finite-time convergence. Firstly, desired surge velocity ud as well as sway velocity vd are designed by combining the hyperbolic tangent function so that zx and zy achieve finite-time convergence. Then, a finite-time term is similarly added during the design of the subsequent control inputs to further accelerate the convergence rate of velocity tracking errors.•The linear anti-windup compensator is able to subtly offset the nonlinear term caused by input saturation, therefore, the input saturation problem will be solved using the linear anti- windup compensator. The results of the simulation experiments show that this controller can still enable the ship to achieve trajectory tracking in the case of input constraints.