Dynamic Positioning System (DPS) is used in FPSO to keep her positional stability in deep waters where the use of conventional mooring systems is generally not available. The Inverse Linear Quadratic (ILQ) optimal servo theory is applied to design control system of DPS in this paper. In this method, it is able to construct a control system which has no interaction among control variables and express an optimal feedback gain in terms of the system matrices and design parameters. Numerical simulations were carried out for some time constants which influence on the performance of the control system.
Floating Production Storage and Offloading (FPSO) drew up oil using a flexible riser from the oil field deep beneath the seabed. She also has the capability to store vast quantities of oil in a similar way to an oil tanker. The oil is transported from FPSO to a Shuttle tanker for transportation to the mainland. In these processes, FPSO is required to maintain her position under external forces such as current, wind and wave. Especially, during the offloading phase, the two vessels should keep their position because they are coupled by a hawser, leading to complex dynamic interaction. The external forces acting on the hull have been largely changed according to the incident angles of external disturbances. Therefore, FPSO is needed to turn toward the incident angles of external disturbances in order to minimize the influence of external forces. This is considerably important to design control system of DPS for both FPSO system and FPSO-Shuttle tanker system. Generally, the Linear Quadratic (LQ) optimal regulator theory is mainly applied to design control system of DPS. However, it is very complicated and difficult to select suitable weighting matrices in the performance index manually to obtain optimal control inputs.