Fixed-Time Leader-Follower Formation Control Of Unmanned Surface Vehicles

With the rapid development of unmanned surface vehicle(USV)technology,single ship motion control system is becoming well-developed and has been widely used in military and civil fields.However,the performance of single ship is not enough to meet operational requirements in a wide sea area which can be made up by cooperative formation control of multiple USVs so as to improve the ability for performing complex water tasks.Therefore,the study on formation control of multiple USVs has great research value and theoretical significance.In this paper,the USVs leader-follower formation system is researched,in which the control methods including cooperative trajectory tracking and fixed-time control algorithm are introduced to improve the convergence performance of tracking control for USVs formation system.Considering the problems of USVs formation tracking control under unknown environment disturbances and unmodeled dynamics,the finite-time precise disturbance observer is designed to identify and compensate unknown information in complex environment,so as to ensure fast and accurate leader-follower USVs formation tracking control.The specific research contents are as follows:First of all,a fixed-time control strategy based on backstepping technology is proposed for the leader-follower USVs formation system.The designed strategy can realize stable formation tracking control within the upper bound of setting time with good convergence.Moreover,the upper bound of convergence time can be obtained independent on initial state of each USV.Lyapunov stability theory strictly proves the stability of the formation system,and the simulation results further verify effectiveness of control strategy.Secondly,a fixed-time control strategy based on finite-time disturbance observer is proposed to solve leader-follower USVs formation tracking control problems under unknown environment disturbances.The designed strategy can ensure fast convergence of formation system and overcome the disadvantage of complex derivative in backstepping technology.At the same time,by introducing finite-time precise disturbance observer,the unknown disturbance can be observed and compensated effectively.The effectiveness and superiority of the formation control strategy are also verified by strict mathematical proofs and simulation experiments.Finally,the fixed-time control strategy is designed combining finite-time unknown observer with nonsingular terminal sliding mode techniques which can solve the leader-follower US Vs formation tracking control problems under unknown disturbances and unmodeled dynamics in complex environments.The proposed strategy can achieve fast convergence and accurate performance for formation tracking control system and overcome the singularity problem in last chapter.And the disturbances term and unmodeled dynamics term are regarded as the lumped unknown term which can be compensated effectively by finite-time unknown observer.Then the precise formation tracking control can be ensured independent on model of each USV.The validity and superiority of formation control strategy are also verified by strict mathematical proof and simulation experiment.