Prescribed Performance Formation Control Of Multiple Unmanned Surface Vehicles

Unmanned surface vehicle(USV)is an intelligent platform for offshore work.Recently,USV plays a vital role in search and recovery,exploration,surveillance,monitoring,and military applications.Formation control is a typical issue of multiple USV cooperation.In practical applications,the steady-state and transient performances of a control system are of great importance.Prescribed performance control(PPC)methodology provides an effective tool for guaranteeing steady-state and transient performances of the control system.The PPC is to design feedback control systems such that the explicitly predefined transient and steady-state performances of formation errors are satisfied.The PPC could guarantee that the formation errors evolve always within predefined allowable regions that are bounded by decaying functions of time,usually chosen as exponential functions.Therefore,it is of great practical value and theoretical significance to study PPC of formation system for USVs.Based on Lyapunov stability theory,backstepping design method,logarithmic barrier Lyapunov function,dynamic surface control(DSC),and graph-based theory,this thesis studies the PPC problem of USV formation system.The main contents of the thesis are outlined as follows.(1)Chapter 2 studies adaptive PPC of USV formation system with uncertain parameters under an undirected communication topology.With the introduction of an error transformation function,the constrained formation control of the original vehicle is transformed into the stabilization of an unconstrained formation system.Then,DSC technique is introduced to avoid the repeated differentiation of virtual controls,and thus there is no need to have the acceleration information of the neighboring USVs in the controller design.Adaptive control technology is applied to estimate the unknown parameters and the upper bound of the external disturbances.Subsequently,a distributed adaptive formation controller is designed using Lyapunov synthesis and backstepping design method.Finally,the Lyapunov stability theory is applied to show that the stability of closed-loop formation error system with prescribed transient performance.The numerical simulation results illustrate the effectiveness of the proposed approach.(2)Chapter 3 studies PPC of USV formation system under communication maintenance and collision avoidance constraints.Firstly,the constraints on collision avoidance and communication maintenance are described by formation error constraints.Secondly,the uncertainties in USV dynamics are divided into two parts: parametric and nonparametric uncertainties.The adaptive control technique is used to estimate the unknown parameters and the upper bound of external unknown disturbances.Adaptive neural network control technique is used to approximate the nonparametric uncertain dynamics.Consequently,logarithmic barrier Lyapunov synthesis and recursive adaptive backstepping procedure are incorporated into the formation controller design to obtain adaptive neural network formation controller,which could avoid collision and maintain the initial communication connection between neighboring USVs,and make the formation errors satisfy the prescribed transient performance.Simulation results showe the performance of the proposed formation controllers.