The Design Of The Ship Nonlinear Trajectory Tracking Controller

The ship trajectory tracking control is investigated in this thesis. The ship trajectory tracking controllers are designed by using two nonlinear control methods, one of which is accurate feedback linearization and the other is Backstepping algorithm.The ship trajectory tracking 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 mathematic model. Secondly, disturbance is always existed in the model used for designing controller. In view of the above problems, it's more important to apply more effective control algorithm to the ship movement control field. And increasing importance has been attached to nonlinear control theory in each field which provides a new inspiration for the ship maneuvering and control.The developments of the nonlinear control theory are summarized in the thesis, especially, two kinds of representative and milestone meaning method—accurate feedback linearization and Backstepping algorithm in recent two decades are discussed which are intercompared herein. Otherwise, Lyapunov stability and the design principle of the accurate feedback linearization and Backstepping algorithm are introduced briefly.The ship movement model is the basis of researching ship's movement control and is high nonlinear. However, linear model is commonly used in most references which is about ship trajectory control. Although some of them use nonlinear ship model, the control results have limitation more or less. In this thesis, based on accurate feedback linearization, a ship trajectory tracking controller is designed for a nonlinear ship surfa- ce movement mathematic model. Furthermore, another ship trajectory tracking controller is designed for the nonlinear ship surface movement mathematic model with constant disturbance which is caused by wind, wave and current change slowly. The design of the controller is based on Backstepping algorithm with integrator.Eventually, the simulation studies for a replica are carried out respectively by utilizing Matlab/Simulink toolbox. The simulation results are satisfied which show that the actual trajectory of the ship can track the desired one and the effectiveness of the controller is verified.