Switched-structure of linear MIMO controllers for positioning of a drillship on a sea surface

In the paper a multicontroller-based switchable control system structure is proposed to control nonlinear MIMO plants. The considered structure contains a set of linear feedback controllers operating together with an additional, statically decoupled loop of the control system. The nonlinear model of a drilling vessel in three degrees of freedom (3DOF) on the sea surface is used as a MIMO plant to be controlled. The system synthesis is carried out by linearization of the adopted nonlinear plant model at its nominal “operating points” that depend on the preset ship yaw angle and the velocity of the see current. Performance of the proposed control systems is illustrated by examples of simulation results carried out in MATLAB/Simulink using the nonlinear model of low-frequency (LF) motions of WIMPEY SEALAB drilling vessel.