Leader-follower Formation Control Of Multiple Unmanned Surface Vehicles With Prescribed Performance Guarantees

Modeling,identification,and control of marine vehicles including unmanned surface vehicle(USV)and underwater robots have recently received a lot of attention from both marine technology and control engineering communities due to their important applications in ocean engineering,such as offshore oil and gas installations,unexploded ordnance hunting,environmental surveying,undersea cable tracking and inspection.The formation control design problem for multiple USVs is far from trivial,and it typically involves several important areas including ocean engineering,control engineering,electrical and communications engineering,machine vision,computer science.Based on the backstepping design method and Lyapunov stability theory,this thesis studies the formation control problem for a group of USVs systems with prescribed performance.Prescribed performance control(PPC)methodology is employed to ensure that the output tracking error responses evolve always within the predefined regions that are bounded by the desired performance functions.The performance function is taken as an exponentially decaying function of time and thus the transient performance(e.g.,overshoot,and convergence speed)and steady-state performance of the tracking error can be specified by adjusting the prescribed boundary function.The transient and steady-state performance of formation control system is also of great importance in practice.Thus,this thesis studies the formation control with prescribed performance for a group of USVs.The main contents are summarized as follows.Chapter 2 studies the leader-follower formation control of a group of fully-actuated USVs under communication range constraints.In the USV formation system,each USV has access to its leader’s states(including the leader’s position,speed,and acceleration)through onboard wireless sensors.However,the communication range of an onboard wireless sensor is often limited.In order to ensure that each USV could reliably obtain its leader’s states,it is necessary to maintain the relative distance between the USV and its leader within their communication ranges.Meanwhile,each USV also needs to avoid collision with its leader.Therefore,the constraint conditions for the communication range and collision avoidance between USV and its leader should be guaranteed in the controller design.A novel tan-type barrier Lyapunov function is employed to guarantee the responses of formation distance error and heading angle error stay always within the bounds of the desired performance functions.The disturbance observer is presented to estimate the external time-varying disturbances on-line.Based on the disturbance observer,a formation tracking controller is designed such that the prescribed transient and steady-state performance of the formation tracking errors is guaranteed,and the constraint conditions for the communication range and collision avoidance are satisfied.Simulation results show the effectiveness of the proposed formation controller.Chapter 3 studies the output-feedback formation control problem for a group of fullyactuated USVs with communication.A one-to-one communication topology is considered,where the leading vehicle is assigned a task to track a desired trajectory and each vehicle except for the last follower(tail agent)communicates only with one leader and with one follower.Assume that the information exchange among the vehicles is limited by some given communication radius.Under the limited communication range,connectivity maintenance and collision avoidance between the leader and follower are considered in the formation control design.To compensate for the modeling uncertainties,neural network(NN)approximators are presented to estimate uncertain dynamics.Based on the dynamic surface control technique,backstepping procedure,NN-based observers,tan-type barrier Lyapunov functions,and control Lyapunov synthesis,a decentralized adaptive output-feedback formation tracking controller is presented to achieve the boundedness of the signals in the closed-loop system,while guaranteeing connectivity maintenance and collision avoidance between the leader and follower during whole operation.Simulation results demonstrate the effectiveness of the proposed formation controller.Chapter 4 studies leader-follower formation control of multiple underactuated USVs based on relative information.Assume that each USV can measure the relative distance and angle between its leader through onboard vision sensors,but has no access to its leader’s state information under the global coordinate(such as the position,attitude and speed information under the global coordinate).We consider the underactuated USV model has nonzero off-diagonal terms in the system matrices.Firstly,a coordinate transformation is used to change the vehicle position such that the vehicle dynamic model becomes a form without off-diagonal terms.Secondly,tan-type barrier Lyapunov functions are employed to guarantee both the relative distance error and relative angle error do not violate the predesigned boundary performance function constraints.The dynamic surface control technology is introduced to avoid the derivatives of the virtual control laws.The high gain observer is presented to estimate the leader’s speeds.Neural network(NN)approximators are employed to approximate the uncertain dynamics.Finally,a decentralized adaptive NN formation controller is presented to achieve the boundedness of the signals in the closed-loop system,while guaranteeing the prescribed transient and steady-state performance.Simulation results demonstrate the effectiveness of the proposed formation controller.