Research On Ship Dynamic Positioning Control And Optimal Thrust Allocation

Dynamic positioning system of a marine vessel is an automatic control system which controls the vessel's position and heading exclusively by means of active thrust to counteract the environmental disturbances and to remain at a fixed location and for precision tracking.The high level control system is the core part of a dynamic positioned vessel,and it is usually separated into two parts:a DP motion controller calculates the desired total force and moment that the propulsion system should produce,and a thrust allocator distributes the command from the motion controller on different thrusters so that the resultant force and moment they produce matches the command.In order to promote the performances of dynamically positioned vessels,this thesis gets involved in the research on dynamic positioning control and optimal thrust allocation of marine vessels,and the main tasks are as following:Firstly,reference coordinate frames are introduced to describe the motion of a ship,a three-degree-of-freedom mathematical model about surface vessels is constructed,and the mathematical model of environment disturbances are also presented.Secondly,based on the discrete-time mathematical model of ship motion,a disturbance observer is proposed.And then,based on the model predictive control principle,a DP motion controller is designed using Laguerre functions.Thirdly,a cost function with the goal of minimizing power consumption and allocation error as well as singularity avoidance is proposed,the constraints are determined according to the physical limits of thrusters.Based on these,an optimal algorithm based on sequential quadratic programming is presented.Moreover,considering that thruster forces and angles change slowly to follow input commands with mechanical constraints,a multi-step optimal algorithm is proposed based on model predictive control.At last,simulation studies on a scale model ship are carried out in Matlab environment,and all the results illustrate the effectiveness of the proposed observer,the control law and the two optimal thrust allocation algorithms.