Finite-time control design for course tracking of disturbed ships subject to input saturation

Abstract

This work considers a finite-time command filtered course tracking problem of ships with unknown bounded disturbances, unmodelled dynamics and input saturation. By melting command filter technique into backstepping design, a finite-time control scheme is proposed, which overcomes the ‘explosion of complexity’ and ‘singularity’ problems resulted from the calculation of repeated derivatives of virtual control inputs in the conventional backstepping method. A hyperbolic tangent function is adopted to estimate saturation with a bounded estimation error in order to guarantee that the saturation function acting on the rudder angle can be differentiable, where the rudder angle is considered as a new state variable whose initial value is zero. The finite-time disturbance estimator is constructed to provide the estimation of compounded uncertain item derived from unmodelled dynamics and external disturbances. Simulation results and comprehensive comparisons are used to demonstrate the effectiveness and superiority of the proposed control scheme.