Path Following And Cooperative Control Of Underactuated Unmanned Surface Vehicles

The 21st century is a century of ocean.Ocean contains rich resources such as biology,oil and gas,mineral products,etc.,and it becomes the strategic space and resource base for the survival and sustainable development of human beings.Unmanned surface vehicle(USV),as an important tool to uncover,explore,and protect the sea,has broad applications in both military and civilian fields.Among the key technologies of USVs,path following and cooperative control are one of the hot topics and research frontiers and attracted increasing attention.This thesis addresses the path following,cooperative path following and kinetic control of underactuated USVs.The main contributions of this thesis are as follows:Firsrly,the path following of underacutated USV is investigated at the kinematic level.LOS guidance,integral LOS guidance and adaptive LOS guidance have been widely used in the path following design of underacutated USVs.However,the classical LOS guidance law is susceptible to sideslip angle,and the integral LOS guidance and adaptive LOS guidance laws can only deal with constant sideslip angle.In addition,integral LOS guidance law may cause phase lag or saturation,and the adaptive LOS guidance law may suffer from oscillation during the transient-state.To solve the above problems,two new LOS guidance laws are proposed for underacutated USVs.Specifically,the path following problem of underacutated USV with unknown sideslip angle is investigated,and a predictor-based LOS guidance law is proposed.The predictor is introduced into the LOS guidance design,and an adaptive law is developed based on the prediction error.Fast identification of the sideslip angle can be achieved,and the path following performance can be improved.By using a cascade stability theory,the equilibrium point of the closed-loop system is shown to be globally uniformly asymptotically stable.Transient analysis shows that the L2 norm of the derivative of the adaptive signal can be reduced by choosing design parameters.The path following problem of underacutated USV with unknown time-varying sideslip angle is investigated,and an extended-state-observer-based LOS guidance law is proposed.A reduced-order extended-state-observer is used to estimate the time-varying sideslip angle.It guarantees that the sideslip angle can be exactly estimated and compensated,and thus contributes to following a desired path with higher accuracy.The input-to-state stability of the closed-loop system is established via cascade theory.It is proven that the transient learning process can be shorten by increasing the bandwidth of the extended-state-observer.Both simulation and experiment results are provided to validate the effectiveness of the two proposed guidance laws.Secondly,based on the above study on guidance of single USV,the cooperative path following of underacutated multiple US Vs is investigated.Most existing studies on cooperative path following of US Vs are dedicated to fully-actuated systems,while underactuated USVs are usually encountered in practical applications.In addtition,they all consider the cooperative path following over multiple parameterized paths,and can only achieve the parallel formation pattern.To solve the above problems,three cooperative path following methods are proposed for underacutated multiple USVs.Specifically,the cooperative path following of underacutated multiple USVs guided by multiple parameterized paths is investigated.By combining the LOS guidance principle and a synchronization scheme in multi-agent systems,a cooperative path following controller is proposed based on a path variable synchronization approach.Consequencely,a parallel formation is achieved along multiple paths.Then,the cooperative path following of underacutated multiple USVs guided by one parameterized path is investigated.By combining the LOS guidance principle and a containment scheme for multi-agent systems,a cooperative path following controller is proposed based on a path variable containment approach.Consequencely,a queue formation is achieved along one curve.Next,the cooperative path following of underacutated multiple USVs guided by one closed curve is investigated.By combining the LOS guidance principle and a cyclic pursuit design,a ring-networked cooperative path following controller is proposed,and a symmetric formation is achieved over the closed curve.Finally,these results are extended to the cooperative path following without using a global reference velocity and in the presence of unknown sideslip.The input-to-state stalility of the closed-loop systems are established via cascade theory.Both simulation and experiment results are provided to validate the effectiveness of the proposed three cooperative path following methods.Finally,the kinetic control of underacutated USVs is investigated at the kinetic level.In the literature,neural networks are widely suggested for compensation of unknown kinetics for USVs.The neural adaptive laws are updated based on the tracking errors,and any nonzero tracking errors during the transient phase can result in control signals of large magnitude.In addition,fast adaptation relys on large adapation gains,while the oscillations will exacerbate with the increment of adaptation gains.Also,input constraints are seldom considered in the existing neural nerwork controller design.To solve the above problems,a predictor-based neural control method is proposed in this paper.Prediction errors are used to update the neural adaptation laws.Fast adaptive compensation of model uncertainties and exteral environmental disturbances is achieved without incurring oscillations using large adaptive gains.By using a saturation function design,the developed controller is bounded with the bounds known as a priori,such that the input saturation can be avoided.The input-to-state stalility of the closed-loop system consisting of the estimation subsystem and the control subsystem is analyzed via cascade theory.Furthermore,the input-to-state stalility of the whole system including the kinematic control subsystem and the kinetic control subsystem is established.Simulation results demonstrate the effectiveness of the proposed kinetic controller for underacutated USVs.