Application of Observer-Based Sliding Mode Controller in Dynamic Positioning Systems

In dynamic positioning, the governing equations of vessel motion are uncertain. These uncertainties are due to unknown environmental disturbances and hydrodynamic coefficients in equations of vessel motion. In previous works concerning uncertainties, it is assumed that the vessel states are fully available and that the position signals are noise free. This paper presents the design of a robust DP system composed of a notch filter, a passive nonlinear observer and a sliding mode control algorithm to remove the assumptions made in previous works. The measured values of position and heading are first filtered by the notch filter, then, the velocity and bias terms are estimated by the observer using the filtered signal. Then they are used in a sliding mode control law for position keeping of the vessel. The simulation results approve of the capability of the proposed control system to deal with uncertainties.