Sliding mode control unified with the uncertainty and disturbance estimator for dynamically positioned vessels subjected to uncertainties and unknown disturbances

Abstract

When considering the characteristics of a dynamic positioning (DP) vessel involving uncertain modelling and unknown disturbances, the vessel control problem becomes a mismatched nonlinear control issue. To resolve this issue, this paper proposes a control method based on the sliding mode control (SMC) and the uncertainty and disturbance estimator (UDE). The total disturbance in the DP vessel is determined using the UDE, whereas the trajectory tracking function of the vessel is achieved via SMC. Moreover, the estimation error in the UDE and the tracking error of the SMC were found to converge based on the Lyapunov theory. The effectiveness of the proposed control strategy was verified via simulations. A comparative study involving the conventional SMC was also conducted, revealing that the proposed SMC unified with the UDE yielded a considerably superior performance.