Adaptive Sliding Mode Control For Trajectory Tracking Of Underactuated Ship

In recent years,with the rapid development of underactuated system control and the increasing demand for intelligent ships,the issue of underactuated ship control has attracted more and more attention.Considering the existence of external environment disturbances,model and unmeasured speed of uncertain ship,state-feedback and output-feedback adaptive sliding mode control strategies of underactuated ship trajectory tracking are proposed combining with advanced control mehods,such as backstepping design method,sliding mode control algorithm,parameter adaptive method,dynamic surface control technology,neural network and low frequency gain learning.Firstly,based on the assumption that the ship model is known,this paper considers the underactuated ship trajectory tracking problem under the known and unknown bounds of environmental disturbances.Furthermore,a ?-modified parameter adaptive law is designed to estimate the bounds of external environmental interference for the unknown environment.The hyperbolic tangent function is introduced to eliminate the chattering problem caused by the introduction of symbolic function.Secondly,aiming at the problem of trajectory tracking control with ship model uncertainties and unknown environment disturbances,dynamic surface control technology,adaptive neural network,sliding mode control algorithm and backstepping design method are combined to design a neural network adaptive sliding mode control law.In order to avoid the "dimensionality disaster" problem caused by neural network and the differential operation directly on the virtual control law,the minimum learning parameter method and the dynamic surface control technique are combined to propose a trajectory tracking adaptive sliding mode control law based on dynamic surface control and minimum learning parameter method.This control law is used to reduce the computational load and avoid the complexity explosion problem.Thirdly,for the control problem of ships trajectory tracking with the unmeasurable actual speed,a nonlinear observer is used to estimate the speed and combined with the dynamic surface control technology to avoid direct derivation of virtual control function,an adaptive sliding mode output feedback control law for underactuated ship trajectory tracking based on nonlinear observer is proposed.The control law can accomplish the control target of the ship's trajectory tracking under the condition that the speed is not measurable.Forther more,considering the uncertainties of ship model parameters,an extended state observer is designed to estimate the ship speed and the composite disturbances and combined with the neural network and the low-frequency gain learning technique,a adaptive dynamic surface output-feedback tracking control method with low frequency gain learning for underactuated ships is proposed.The strategy can avoid the phenomenon of high frequency oscillation of the control signal caused by external disturbances.Finally,in simulations test are carried out on a long-range patrol vessel named Singapore BAY CLASS and the effectiveness of the proposed tracking control methods is verified.The results show that the controller designed in this paper can effectively overcome the influence of external environment disturbances and the perturbation of model parameters to complete the task of ship track control.