The Design Of The Ship Dynamic Positioning System Controller Based On Backstepping

Considering the disturbances from the ocean environment such as wind,wave and current,the ships will move under disturbing effect when they are operated on the sea. If we want a ship maintain a certain position in the sea,or when the position deviations occurs,the ship can automatically return to the setting location,the capabilities to produce anti-force and anti- torque are needed.The use of thrusters to provide force and torque to resist the environment force and make the ship maintain the required position is an ideal method known as dynamic positioning.The system using thrusters to control the ship location and heading is just the so-called ship dynamic positioning system.The ship dynamic positioning control become a nonlinear control problem because of the characteristics of ship's dynamic with large inertia,delay and nonlinear etc.and the influence of the environmental factors such as wind,wave and current etc.when ship is in navigation.It doesn't meet the control performance and the system robustness by far that we use the traditional PID and the conventional control strategies.Therefore, there are problems which need to be further researched in this field.Firstly,nonlinearity is not included in the ship movement mathematical model.Secondly,disturbance is always existed in the model used for designing controller.In view of the above problems,how to make use of some more effective control algorithms in the field of dynamic positioning control become more and more important.Therefore,this thesis in particular discussed the most representative,and a milestone in the non-linear design method in the past 20 years,that is,Backstepping algorithm.This thesis has researched the ship dynamic positioning problem based on Backstepping algorithm,and established the non-linear dynamic positioning ship mathematical model with uncertain disturbance.Two kinds of non-linear robust controller for ship dynamic positioning are designed basing on Backstepping method. First of all,controller for the uncertain disturbance model with border known is designed,and the global stability control is achieved.Taking into account the impact of the harsh environment to the ship,controller with disturbance border unknown is designed,and it is proved to meet the L₂ control standard.Eventually,the simulation studies for a replica are carried out respectively by utilizing Matlab/Simulink toolbox.The simulation results show that the actual position of the ship can track the desired one and the effectiveness of the controller is verified.