Nonlinear Backstepping Design Of Ship Steering Controller

The robust adaptive Backstepping design and its applications to nonlinear ship steering control are systemically studieded in this paper. Backstepping design is a new recursive nonlinear control methodology which associated with Lyapunov stabilities theory. After a brief review of conventional nonlinear system control theory and Lyapunov stability, this thesis introduces basic backstepping tools. Then it concludes its advantages and disadvantages by comparison Backstepping and Absolute Feedback Linearization methods. Now two problems listed below are difficult to solve in ship steering controller designs: 1) nonlinear maneuvering characteristics in ship steering control ;2)uncertainty in nonlinear ship responded model. In this paper, it will show how Backsteeping can be applied to solve these problems successfully.Backstepping is related to Absolute Feedback Linearization. However the latter requires precise models and cancels all nonlinearities but Backstepping not. It exploits "good" nonlinearities while "bad" nonlinearities are dominated. So the controller's energy can be reduced and the robustness obtained.The result of simulation is satisfied.In ship steering controller design, the nonlinear ship model should be written in SISO strict feedback form. We start the recursive design with the system first state variable and continue with the second one. By introducing a change of coordinates, we choose Lyapunov functions to stabilize the system and obtain the control law. A nonlinear ship steering controller is designed successfully. Even considered the noises caused by wind, wave and current, the MATLAB simulation tracking error is almost zero. Simulation results show that the presented algorithm is effective and robust.On account of the uncertainty existing in the nonlinear ship responded model, we design a dynamic adaptive ship steering controller by using adaptive Backstepping. After deducing the update law of the unknown constant, we choose the controller gains to guarantee the closed loop system and the control signal global boundedness.