Research On Robust Adaptive Trajectory Tracking Control Of Surface Vessels

The trajectory tracking control of vessels is to force the actual trajectory of vessels to track a desired reference trajectory under a control law.The vessel in navigation is inevitably subject to unknown time-varying environmental disturbances,dynamic uncertainties and input saturation constraints.For the above problems,the following research works are carried out in this dissertation.1.In the presence of the partial dynamic uncertainties,unknown time-varying environmental disturbances and input saturations,the trajectory tracking control problem of vessels is formulated as the tracking control problem for a class of uncertain strict-feedback nonlinear systems under input saturations.For this problem,a novel robust adaptive neural network(NN)tracking control scheme is presented combining adaptive NN,"minimum learning parameter(MLP)" technique and auxiliary dynamic system(ADS)with the command filtered backstepping design tool.Base on the proposed design method,a robust adaptive NN trajectory tracking control law of vessels is designed,which not only reduces the computational burden remarkably,but also prevents the input saturation from destroying the learning capabilities of adaptive laws,and improves the performance of the trajectory tracking control system.2.In the presence of the dynamic uncertainties,unknown time-varying environmental disturbances and input saturations,the trajectory tracking control problem of vessels is formulated as the tracking control problem for a class of uncertain nonlinear systems with unknown control gains under input saturations.For this problem,a hyperbolic tangent function is introduced to approximate the input saturation nonlinearity and a new nonlinear function featured by the practical control idea of "small-error large-gain and large-error small-gain" is constructed,then based on the above,a novel robust adaptive NN tracking control scheme is presented combining nonlinear tracking differentiator,Nussbaum-type function,adaptive NN and MLP technique with the backstepping design tool.The proposed control schmem can balance the feedback control gain and system control performance and improve the control performance.The proposed control design method is used to design a robust adaptive NN trajectory tracking control law of vessels.Further,output constraints of the trajectory tracking control of vessels being taken into account,a novel nonlinear transformation is constructed to transform this output constraint problem into the boundedness problem of transformed variables,then a robust adaptive NN trajectory tracking scheme is developed incorporating the adaptive NN technique,ADS into dynamic surface control method.The proposed control scheme can handle various types of output constraint boundaries including static,time-varying,symmetry and asymmetry ones in a unified framework.3.In the presence of the dynamic uncertainties,unknown time-varying environmental disturbances and input saturations,the trajectory tracking control problem of vessels is formulated into the tracking control problem of uncertain strict-feedback Euler－Lagrange systems under input saturations.For this problem,a robust adaptive finite-time tracking control scheme is proposed using finite-time stability theory,adaptive neural technique and novel ADS.Further,a Gaussian error function is used to approximate the input saturation nonlinearity and the compounded uncertainty term synthesizing dynamic uncertainties and unknown time-varying environmental disturbances is transformed into a linear parametric form with a virtual unknown parameter,on this base,a robust adaptive finite-time trajectory tracking control law of vessels is designed combining parameter adaptive technique with vectrotial backstepping design tool.The designed control law only needs to estimate one unknown parameter,which is simple to compute and easy to implement in engineering applications.4.To verify the effectiveness of the above proposed trajectory tracking control schemes,simulations on a model vessel as test objec are carried out utilizing the Matlab/Simulink toolbox.Simulation results verify that the proposed trajectory tracking control schemes can effectively solve the trajectory tracking control problems of vessels subject to dynamic uncertainties,unknown time-varying environmental disturbances,input saturations and output constraints,which enables the actual trajectory of vessels to track the reference trajectory with the acceptable tracking control performance.