Composite anti-disturbance dynamic positioning of vessels with modelling uncertainties and disturbances

This paper presents a composite anti-disturbance control scheme for the dynamic positioning (DP) of the surface vessels with modelling uncertainties and ocean environmental disturbances. The composite control design builds on integrating the disturbance observer together with the H-infinity optimal control. The composite control structure consists of the inner layer disturbance compensator and the outer layer attenuation controller. The inner layer disturbance compensator rejects slowly varying disturbances due to wave drifts, utilizing estimations from the disturbance observer. The outer layer attenuation controller attenuates norm-bounded disturbances due to residual filtered wave-induced disturbances as well as modelling uncertainties. The composite control scheme provides the computational efficiency. The DP motion closed-loop analysis proves that the composite anti-disturbance control maintains the vessel's position and heading at the reference points and guarantees the closed loop control stability. Simulations and comparisons on a supply vessel verify the availability and the superiority.