Adaptive Formation Control For The Cooperation Of Autonomous Surface Vehicles

With the rapid development of marine unmanned technologies,autonomous surface vehicle(ASV)has become an important tool to perform various missions,such as marine environmental monitoring,search and rescue on water,etc.Advantages of an ASV are low cost,good mobility and no casualties.In order to extend the coverage and improve the fault tolerance and working efficiency of the ASV,the cooperation of ASVs has received increasing attention.During the cooperation of ASVs,formation control plays a significant role,which relies not only on the cooperative scenarios,but also on the characteristics of ASVs and the formation constraints.Existing theoretical researches on formation control of ASVs are mainly faced with the following problems.First,completing regular tasks such as formation keeping and straight-line sailing are unable to meet the requirements of complex cooperative motion scenarios,where the group of ASVs should have the ability to realize desired formation maneuver according to temporary tasks.Current literature still focuses on the formation problem of ASVs under fixed formation configurations.There is little work on formation maneuvering control of ASVs under variable formation configurations.Second,the dynamics of ASVs are nonlinear,strongly coupled and of uncertainties when working on water.The ASVs also suffer from external disturbances,such as wind,wave and current.Although present formation control methods based on neural networks or adaptive techniques can enhance the robustness of the formation system of ASVs against uncertainties and disturbances,their conservatism and computation are still to be discussed.Third,some cooperative scenarios of ASVs require specific transient and steady state performance of formation tracking errors.Constrained actuator capabilities or actuator faults will also affect the formation tracking performance of ASVs.If the existing formation control methods of ASVs encounter such formation tracking performance constraints or actuator constraints,their formation control performance will be greatly degraded.In general,variable formation configurations,uncertain dynamics,external disturbances and various formation constraints have brought great challenges to the development of the formation control theory for ASVs.Aiming to deeply understand the coordinated motion characteristics of ASVs and to improve the robustness,fault tolerance,real-time performance of formation control methods and their applicability under different formation constraints,this dissertation explains the cooperative mechanism of ASVs from three aspects,i.e.,cooperative model,information interaction and formation configuration.Based on graph theory,bearing rigidity theory,backstepping and adaptive control theory,adaptive formation control methods for the cooperation of ASVs are further investigated in this dissertation.The uncertainties,external disturbances and various formation constraints are fully considered.In the case of no or local information interaction among ASVs,formation control problems of ASVs with fixed or variable formation configurations are discussed,respectively.Many formation control tasks of ASVs are obtained,such as shape keeping,formation translation,formation maneuver in curved trajectories or alterable sizes,which provides a theoretical support for cooperative applications of ASVs.Main contributions of this dissertation are as follows.1)For a formation system of underactuated ASVs based on the leader-following dualagent cooperative model,a line-of-sight(LOS)range and angle based adaptive output-feedback formation control method is proposed,which can solve the formation control problem of ASVs with fixed formation configurations in the case of no information interaction.The formation controller of each ASV only needs to update two learning parameters online while suppressing uncertain dynamics and external disturbances,which leads to less computation.The fault tolerance and real-time performance are improved when guaranteeing the robustness of the formation system of ASVs.On this basis,a robust adaptive formation control method using the adaptive programming of the virtual vehicle is proposed,which can solve the formation maneuver control problem of ASVs in curved trajectories with variable formation configurations when there only exists the interaction of yaw angles.Using this method,each ASV merely needs to use inertia coefficients in the model to obtain effective estimations of external disturbances.The disturbance observer and the formation controller in the proposed method share the same set of neural networks.Both of them have only two parameters to be tuned online,which reduces the computation.The formation tracking accuracy of ASVs is improved when maneuvering in curved trajectories.2)For a formation system of ASVs based on the multi-agent cooperative model,a distributed robust adaptive formation control method only using the interaction of position vectors is proposed,which can solve the cooperative formation control problem of ASVs with fixed formation configurations in the case of local information interaction.The proposed method does not need to transmit velocities of three channels of neighboring ASVs,leading to less local information exchange.The neural networks based formation controller of each ASV has only one online learning parameter in three channels,which can not only suppress model uncertainties and external disturbances,but also guarantee the real-time performance of the algorithm.On this basis,a displacement based distributed adaptive fault-tolerant formation control method is proposed,which can solve the cooperative formation control problem of ASVs in the case of partial actuator failure and performance constraints of formation tracking errors.If the interaction topology of ASVs is connected,this method can be utilized to achieve desired fixed formation configurations.The overshoot,convergence rate and steady state accuracy of the neighboring formation tracking errors of each ASV can also satisfy the prescribed performance.3)For a formation system of ASVs based on the multi-agent cooperative model,a bearingbased distributed robust adaptive formation scaling control method is proposed,which can solve the formation scaling maneuver control problem of ASVs in the case of input saturation constraints and uncertainties.The core idea of the developed method is that,leader ASVs programme target formation trajectories and follower ASVs make formation tracking.The parameter compression mechanism and auxiliary system design are introduced into the formation controller of each ASV,which simplifies the weight updating process when dealing with uncertainties and reduces the negative impact from the limitation of actuator capacities.Using this method,if the augmented formation is infinitesimal bearing rigid,not only the prescribed formation shape of ASVs can be maintained,but also the desired formation scaling maneuver is able to be achieved.The proposed method can actively scale and adjust the formation size of the whole group of ASVs as long as the leader ASVs are programmed appropriately.In this process,control inputs of the follower ASVs do not need to be redesigned,and the yaw angle of each ASV can reach consensus.