Robust Global Sliding Model Control for Water-hull-propulsion Unit Interaction Systems - Part 1: System Boundary Identification

Original scientific paper Unexpected severe hull deformation caused by the wave loads would significantly influence the dynamical behaviours of the propulsion system in large scale ships, resulting in degradation of the ship control performance. A new global sliding model control (GSMC) for marine water-hull-propulsion unit systems is proposed to obtain more accurate control performance in this paper. The GSMC was firstly employed to establish the marine propulsion control model with nonlinear uncertainties. In the GSMC model, the saturation function method is applied to eliminate chattering on the sliding surface. Then the Lyapunov stability criterion is adopted to confirm the stability of the control system. Following, for the first time, the boundary problem of the nonlinear model uncertainties were investigated quantitatively. The bounded nonlinear model uncertainties required in the proposed GSMC model, involving engine torque loss / variations, power transfer for various load conditions and shaft rotational speeds, were derived based on the experiments carried out on a marine shaft-line test-bed of the integrated propulsion system as well as a sea trial implemented for a running bulk carrier. An upper boundary of 1,85 % for the model uncertainty has been obtained, which would be introduced into the GSMC for the integrated marine propulsion system to derive the total control law realising the robust control of the system.