Research On Stabilization Control Methods For Underactuated Surface Vessels

Underactuated surface vessel is the object of this thesis,which has no lateral control device.Researching on underactuated surface vessel can reduce the weight of the vessel and save the cost.So more and more attention has been paid on underactuated mechanical systems in recent years.Stabilization control is one of the basic motion control of underactuated surface vessels.The control methods which maintain the position and attitude of the vessel in the ocean are all within the scope of stabilization control.Therefore,it has great theoretical significance and practical value to study the stabilization control method of underactuated vessels.Thesis completes the following aspects:Firstly,the vessel's 6-DOF model is established,and the 3-DOF model of the underactuated surface vessel is obtained after a reasonable simplification.In order to prove the rationality of the model and analyze the system characteristics,the steady-state direct-running and swinging simulations are carried out with the MATLAB software.Secondly,a simple robust stabilization controller is designed.The differential homeomorphic transformation of the original system is carried out without considering the disturbance and a simple robust controller is designed based on the Lyapunov direct method.The controller can stabilize the underactuated vessel from any position to the desired position.In this paper,the form of the simple robust controller is very simple and easy to implement in engineering.According to the stability analysis,the controller has good robustness with respect to the uncertainty of the model parameters.Thirdly,considering the disturbance and model uncertainty,a new type of stabilization controller is designed by combining the backstepping technique and the adaptive fuzzy method.The global differential homeomorphic transformation is used to transform the original system into two subsystems with strict cascade relationship,and the controllers are designed for the two subsystems.The fuzzy system is employed to approximate the uncertain term induced by the unknown time varying environment disturbances in the control law.The adaptive law can change the controller parameters according to the dynamic characteristics of the controlled object,and has better control effect.The controller can achieve the stabilization of position and attitude.Compared with the adaptive sliding mode controller in the simulation,it is proved that the transient performance of the controller designed by this paper is better.It is more compliable with the practical requirements.