Adaptive Integral Fast Iterative Terminal Sliding Mode Control Scheme for the Dynamic Positioning of Ships

In this paper, an adaptive integral fast iterative terminal sliding mode control (AIFITSMC) scheme for the dynamic positioning (DP) of ships subjected to unknown compound disturbances (model uncertainties and environmental disturbances) is proposed. First, based on a fast iterative terminal sliding mode surface, we propose an integral fast iterative terminal sliding mode control (IFITSMC) scheme, whereby the integral item of the sliding mode is bounded, strengthening the transient response and steady state performance of the dosed-loop system. Second, a novel finite-time disturbance observer is incorporated into the proposed IFITSMC structure, which facilitates low steady-state errors and strong robustness to disturbances. Simulation studies and comprehensive comparisons with the traditional fast terminal sliding mode control (FTWC) scheme and the traditional sliding mode control (SMC) scheme demonstrate remarkable performance and the superiority of the AIFITSMC scheme in terms of a rapid convergence rate, excellent steady-state performance and superior disturbance rejection ability.