Study On Nonlinear Control Of Underactuated Ships

Over the past few years,along with the increasing development of Control technology for underactuated systems and the demand for automatization of ships, studies on nonlinear control of underactuated ship have very important significance in practice.Nonlinear control methods of underactuated ship can improve performance, safety and economy of ship navigation.And also,because underactuated ship is as a kind of serious nonlinear systems,researches for it have quite important theoretical values.So studies on nonlinear control of underactuated ship are a worthy subject and have been one of hot issues in the field of ship motion control.In this paper,based on deeply analysis of native and foreign research results on control problem of underactuated ship and summary of existing problems in these results,the problems of underactuatde ship of nonlinear control including stabilization control,path following and formation control are systematically studied,.The contents are as follows:Firstly,stabilization control of underactuated ship.Under assuming that the off-diagonal terms of intertia and damping matrices are nonzero,a model of underactuated ship system is established.Based on backstepping technique and the cascaded approach,the appropriate controller is designed.Numerical simulations are provided to validate the effectiveness and correctness of the proposed controller.Secondly,path following control of underactuated ship.considering the impact of environmental disturbances induced by wave,wind and ocean,a tracking model of underactuated ship is attained.And then,utilizing backstepping technique and the method of sliding mode control,a tracking controller is proposed for underactuated ship to follow a set path with a certain velocity.Furthermore,good robustness of underactuated ship is represented by this controllerThirdly,formation control of ship fleet.Based on leader-follower method,a model of underactuated ship fleet is built.And according to the object of formation control of ship fleet,a suitable controller is designed for follower ship to make the total ship fleet keep a certain formation.Simulations by matlab/simulink proved that control targets are achieved with the proposed controller.Finally,the main conclusions of this paper are summarized,And,the work for future research is put forward.