In this paper, a disturbance observer enhanced model predictive controller (MPC) which compensates for the wave-induced disturbance magnitude and rate is proposed for the ship roll motion stabilisation problem. The velocity model of the ship roll motion is used in the controller design to handle slowly varying modelling uncertainties and external disturbances. The rate of change of the disturbances induced by waves is then attenuated by formulating a control input that incorporates the estimated disturbance rate such that it is always in opposition to the rate of the environmental disturbances. The disturbance estimation was achieved by designing an observer based on convex optimisation formulated as an H2 minimisation problem. Numerical simulation studies, under various conditions of the sea, showed the effectiveness of the proposed MPC scheme in reducing the undesired ship roll motion induced by sea waves.
- ship roll stabilisation
- fin stabilisation
- model predictive control
- disturbance rejection
- disturbance rate compensation