The Fuzzy PID Control And Optimization Research Of Ship Dynamic Positioning System

Ship dynamic positioning system is widely used in commercial ships,scientific research ships,offshore oil drilling platforms,underwater vehicles and warships because of its outstanding advantages over traditional mooring systems in track keeping and position keeping.With the development of deep-water and ultra-deepwater marine exploration,the requirements for the dynamic positioning accuracy of ships are also increasing.The thesis combines PID control,fuzzy control,particle swarm optimization algorithm to study the dynamic positioning of ship.The thesis studies the transformation between fixed coordinate system and hull coordinate system,deduces the ship's 6-dof motion mathematical model according to the rigid body motion theory,and simplifying get the ship's 3-dof motion mathematical model,finally establishes the wind,wave and flow interference force model.The transfer function of ship object is derived based on the obtained 3-dof motion mathematical model and ship object parameters.A double closed-loop control system is designed for the motion characteristics of ship object.The speed is controlled by the inner loop,the conventional PID controller or fuzzy PID controller is adopted,the displacement is controlled by the outer loop,and the proportional controller with limit is adopted.The fuzzy PID controller has been designed,the principle of fuzzy PID controller has been analyzed,the fuzzy domain and membership function have been determined,and the control rules have been established.In the MATLAB environment,the conventional PID control and fuzzy PID control have respectively been simulated,and the simulation results have analyzed to verify the effectiveness of fuzzy PID controller in system fixed-point positioning and anti-interference.Aiming at the difficulty in parameter setting of the fuzzy controller,an improved particle swarm optimization(PSO)algorithm has been adopted to optimize the fuzzy parameters of fuzzy PID controller of ship dynamic positioning system.An improved particle swarm optimization algorithm has been proposed based on the standard particle swarm optimization algorithm.The main strategy of the algorithm is to update the population size through estimating the evolutionary state of particles.The inertia weight and learning factor are updated automatically according to the fitness value of particles,and judge whether the state of particle evolution is normal by the updating state of local optimal fitness value and all optimal fitness value,so as to re-initialize the particles,increase the diversity and convergence speed of the population.The designed system has been simulated.Simulation results show that the optimized fuzzy PID controller has stronger anti-disturbance ability than the conventional PID controller and the unoptimized fuzzy PID controller in the positioning process.