Research On Formationcontrol Of Autonomous Surface Vehicles

In recent years,the marine resources have attracted more and more attention.Scientists from all over the world have conducted increasing researches of marine equipment,and strive to occupy the commanding heights in the field of marine resources exploration and development.In numerous marine equipment,autonomous surface vehicle(ASV)is getting more and more attention of scientists from all over the world due to wide scope of activities,low cost,and high independent ability.ASV related technology has developed rapidly,but a single ship has poor robustness,and is not suitable for a wide range of areas.In practice,therefore,many ASVs need to coordinate with each other so as to achieve a particular goal.Compared with a single ship,multi-ASV has higher efficiency,stronger fault tolerance and stronger adaptability through collaborative operation.With full-actuated ASV and underactuated ASV as the research objects,in-depth research is conducted on ASV formation control with the combination of the related knowledge of graph theory,nonlinear system stability theory,dynamic surface control technology,sliding mode control technology and command filtering technology.The main work includes the following aspects:(1)To solve the formation control of full-actuated ASV under disturbance,leader-less formation control strategy,leader-follower formation control strategy and multi-leader formation control strategy are proposed.First of all,in the design of the first two kinds of control strategy,a nonlinear disturbance observer is designed to estimate the external disturbances online.Next,with the output of the observer as compensate term and combining with dynamic surface control technology and related knowledge of graph theory,the robust formation control of full-actuated ASV is realized.In addition,as for multi-leader robust control problem,a disturbance observer with finite time convergence properties is proposed with the combination of finite time stability theory.Then,like the other two kinds of control design,a type of robust containment control strategy is designed with the combination of containment control theory knowledge,and dynamic surface control technique,and multi-leader formation control is solved.Finally,the closed-loop systemstability is proved by combining with Lyapunov stability theory.(2)To solve the robust formation control problem of underactuated ASV under external disturbance and hydrodynamic parameter uncertainties,this paper proposes a robust formation control strategy based on upper-to-up sliding mode.By referring to“Ponit-to-Point” navigation theory,the algorithm converts formation control problem to the coordination of the path tracking error and the heading angle tracking error.Firstly,the virtual control law with saturation characteristics is designed in the kinematic loop through knowledge of graph theory.Then,in the dynamic loop design,the corresponding virtual control law that can allow the lateral speed and heading velocity of the ship to track is designed through the design of the actual control input.In the end,the stability of the closed-loop system is proved through cascade system stability theory.Additionally,on the basis of the previous algorithms,the robust formation control strategy based on communication time delay is proposed.Simulation results show that the algorithm is still effective under the condition of the communication time delay and external disturbance.(3)In order to make underactuated ASV achieve formation control within a finite time under external disturbance and hydrodynamic parameters uncertainties,a finite time robust formation control strategy is proposed by combined with graph theory and upper-to-up sliding mode.To begin with,the control problem is decomposed into two parts,namely,kinematic loop design and dynamic loop design through back-stepping.Then,the surge and sway velocity is designed in the kinematics loop through the theory of finite time and the related knowledge of graph theory so as to realize the coordination of ship locations within the finite time;the tracking of actual velocity for reference velocity is achieved in the kinematics loop design with finite time sliding mode control method.Finally,the simulation proves that the controller has good robust performance for external disturbance.(4)In order to solve the multi-leaders robust control problem of underactuated ASV under external disturbance and hydrodynamic parameters uncertainties,this paper proposes a robust containment control strategy with the combination of the related knowledge of command filtering method and contaiment control as well as upper and lower bound sliding mode method.At the beginning,the kinematics model is expressed in a strict feedback form so as to design the control strategy with command filtering back-steeping method.Then,combining with the related knowledge of graph theory and using course angle and headingvelocity as the control input,related virtual control law is designed.The corresponding virtual control law and its derivative estimation are obtained by putting the virtual control law of course angle and heading velocity in the first-order filter.Then,the heading velocity is used as the input control to narrow the deviation of course angle and the virtual control law.Command filter is introduced to estimate the virtual control law online,and the nonlinear term is compensated by introducing compensation signal.Finally,the external disturbance and model uncertainty are inhibited by introducing upper-to-up sliding mode method.The simulation results prove the effectiveness of the proposed control strategy.Furthermore,for the robust contaiment control problem,based on dynamic surface control and upper-to-up sliding mode,a new control strategy is put forward.This method overcomes problem of the last method which must assume the speed is non-zero,and realizes the robust contaiment control under any condition.(5)Based on underactuated asymmetric ASV formation control problem under full state control,a time-varying formation control strategy is designed.First of all,through the introduction of a global differential homeomorphism change and the input coordinate transformation,the underactuated ASV formation control problem is transformed into a new stabilization problem of nonlinear system.Then,the system is divided into two subsystems and applied to nonlinear cascade systems stability theory.The stabilization problem of the new system is simplified to be the stabilization problem of a nonlinear fourth-order subsystem.Finally,for the fourth order subsystem,smooth time-varying feedback control law is designed in two steps by means of the theory of time-varying control system,and the global K exponential stabilization of the system is realized.The simulation proves the proposed control strategy is effective.