Research On Control Of Ship Dynamic Positioning System Based On Nonlinear Observer

With the increasing shortage of land and offshore resources,human beings are paying more and more attention to the development and exploration of deep-sea resources,and the dynamic positioning system is a necessary support system for ships operating in the deep sea areas.The dynamic positioning system can offset the external environmental disturbance by means of its own thruster,and locate itself at desired position on the sea or sail along a preset trajectory with a certain attitude.However,the environment of the deep sea areas in which the ship is very complicated,and there are obvious uncertainties in the dynamics of ship and the environmental disturbances the ship has suffered.In addition,there exists noise in the ship's measurement signal,and accurately measuring the velocity of the ship is difficult.Therefore,researches are launched for the positioning control problems of the ship,aiming at prolonging the service life of the propulsion equipment,reducing the energy loss,enhancing the performance of the dynamic positioning control system,and improving the positioning control accuracy of the ship.The main research work is as follows:1.Aiming at the problems that the ship dynamic positioning system measurement signal was accompanied by high frequency signal,and the ship motion speed was difficult to accurately measure,a nonlinear passive observer was designed based on the dynamic positioning system model,and the global stability proof was given by using Lyapunov's theorem.At the same time,the particle swarm optimization algorithm was introduced to optimize the observer gain parameters,which solved the problem of setting the unknown gain parameters of the observer.The observer can effectively filter out high-frequency motion components,reconstruct low-frequency signals from the output with measurement noise,and estimate ship motion velocity and environmental disturbance power.2.Aiming at the control problem of dynamic positioning ship subjected to unknown time-varying disturbance,based on the design of nonlinear passive observer,a nonlinear proportional-differential(PD)control law was designed by using Lyapunov function.The closed-loop control of the whole system was realized by feedback of the estimated value of the non-linear observer to the PD control law.The stability of the designed control law was proved by Lyapunov theory and cascade nonlinear systems.Subsequently,in order to further improve the speed response and control accuracy of ship control system,a dynamic positioning nonlinear robust control law was designed by using nonlinear passive observer,integral action and vector backstepping control method.The global stability of the system was proved by using Lyapunov theorem.Finally,in the environment of Matlab/Simulink,a dynamic positioning supply ship is taken as the numerical simulation experiment object.The simulation results show that the designed dynamic positioning control system can effectively solve the problems of high frequency noise,difficult to accurately measure velocity and unknown time-varying disturbance estimation in ship measurements,so that the ship can be accurately positioned in the desired position under different sea conditions and realize the ship dynamic positioning.