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A Nonlinear Observer for Ship Dynamic Positioning System

State estimation plays an important role in ship dynamic positioning control system and is one of the hot issues in this field. Aiming at the problem of state estimation of dynamic positioning control for three degree of freedom ship on water surface, a design method of sliding mode observer is proposed by using the characteristics of sliding mode variable structure control which is fully adaptive to parameter perturbation. Based on the low-frequency and high-frequency mathematical models of the three-degree-of-freedom ship, the low-frequency position and velocity are estimated by the sliding mode formed by the velocity observation error, the hyperbolic tangent function is used as the switching function, and the passivity theory and Lyapunov stability judgment are used. The passivity theory and Lyapunov stability criterion are used to analyze and prove the stability of the observer, and the gain matrix of the observer is determined based on the frequency domain analysis method. Taking a supply ship as an example, the designed sliding mode observer is simulated and analyzed, and the simulation experiment of the sliding mode observer is carried out under the condition of sea state change. Theoretical analysis and MAT LAB simulation results show that the proposed sliding mode observer has good robustness to environmental disturbances.