An adaptive sliding mode control method for dynamic positioning vessel: Mitigating potential instability arising from auxiliary systems

This paper presents an adaptive sliding mode control (SMC) strategy for dynamic positioning (DP) vessels with the model uncertainty, environmental disturbances, and input saturation. The adaptive updating laws for the parameter estimation are derived using Lyapunov theory. The low-level thrust allocation and the actuator limitations are considered. It is theoretically proved that all signals in the closed-loop system are uniformly ultimately bounded (UUB). The importance of the auxiliary system within the adaptive controller is highlighted, and potential instability issues when combined with thrust allocation are explored. Two methods to mitigate this instability are proposed and verified by numerical simulations. These methods achieve harmonious cooperation between high-level motion control and low-level thrust allocation by actively adjusting the target thrust values and auxiliary system parameters. Simulation results demonstrate that the proposed adaptive SMC are capable of maintaining DP vessel stability under the given uncertainties and disturbances.