Path Following Control of Ship Based on Time-Varying Threshold Prescribed Convergence Law Sliding Mode

Considering the nonlinear and strongly coupled model of under-actuated ship with unknown external random wave disturbance, the heading compensation angle of the ship can be obtained via S-surface guidance base on yaw-error. The problem of lacking control accuracy caused by traditional prescribed convergence law (PCL) sliding mode under high-frequency interference is solved by designing a new time-varying threshold PCL sliding mode control (PCLSMC) and introducing nonlinear adaptive factor into S-surface guidance at the same time. This new navigation and control system makes the movement of the state varibables relative smooth near the sliding mode surface, and guarantees system state variables both having a finite-time convergence and reducing the overshoot of heading angle. Simulation results prove that the proposed guidance and control method is capable of producing smooth reference heading angle and decreasing overshoot for the system, which shows a better robustness.