Non-switching reference trajectory based discrete-time sliding mode path following control for dynamic positioning ship with time-varying disturbances

Abstract

This paper investigates the discrete-time sliding mode (DSM) path following control problem for dynamic positioning ship (DPS) with time-varying disturbances and sideslip based on non-switching reference trajectory and discrete-time disturbance observer (DDO). Initially, a high-order DDO and a finite-time sideslip angle observer are designed to observe the time-varying disturbance and sideslip angle, respectively, to compensate for their effects on DPS. Then, the discrete-time integral sliding mode surface is designed by introducing the nonlinear integral with characteristics of small error amplification and large error saturation, which avoids the system instability due to integral saturation. Furthermore, a new DSM path following controller is designed based on the new reaching law composed of disturbance observation errors and non-switching reference trajectory. The conclusion that the position tracking error can asymptotically converge to zero is inferred. The proposed control scheme avoids the problem that the continuous-time control law is not suitable for the actual shipborne discrete-time controller and the system chattering caused by switching functions and simultaneously ensures the system’s anti-disturbance ability. Finally, comparative simulation results verify the effectiveness and superiority of the proposed control scheme.