An enhanced trajectory tracking control of the dynamic positioning ship based on nonlinear model predictive control and disturbance observer

Abstract

This paper proposes a robust control approach based on nonlinear model predictive control (NMPC) for dynamic positioning (DP) ships subject to unknown time-varying disturbances with the physical limitation of thrusters. An improved nonlinear disturbance observer (INDO) based on super-twisting control is constructed for disturbances estimation and attenuation. Furthermore, the NMPC optimization problem is formulated to reject the disturbances by combining the disturbance estimates into the prediction model. To mitigate the difference between commanded forces and actual forces, the low-level thrust allocation algorithm is integrated into the high-level motion controller. In light of this, a detailed time-iteration NMPC algorithm for DP ships is presented. Numerical simulations based on the INDO-based NMPC (INDO-NMPC) strategy under the scenario of trajectory tracking are performed to explore the robustness of DP system. Theoretical analysis and simulation results well prove the effectiveness and superiority of the proposed control law.