DP 시스템을 위한 실시간 비선형 추력분배 알고리즘

Abstract

Several real-time nonlinear thrust allocation algorithms for dynamic positioning(DP) system are studied in this study. The DP system is generally defined as a system that automatically controls the position and heading of an offshore vessel by means of active thrusters’ action to keep it in a predetermined area, for station-keeping, for tracking, for precise maneuvering, and for other positioning tasks. Normally offshore DP vessels have more numbers of thruster than the degree of freedom(DOF) for the planar motion of a vessel that is the control target motion of the DP system. From this over-actuated characteristic, an optimization problem arises which should map the calculated control forces and moment from the DP controller in 3 DOF into each thruster’s action that are more than three. Moreover, this optimization problem should be solved in real-time because this mapping must be done in each feedback loop. In this study, several nonlinear optimization techniques based on the method of the Lagrange multiplier are examined with various cost functions and constraints. The feasibility and performance of the optimization methods for thrust allocation of a DP vessel are reviewed with time-domain simulation.