Research On Coordination Control Of Multiple UUVs In Complex Environment

With the progress of technology and the shortage of resources,the exploitation of the ocean have gradually developed from the neritic areas to the abyssopelagic areas,which is accompanied by higher requirements for the efficiency and automation of marine operations.As an important tool for ocean exploitation,although the unmanned underwater vehicle(UUV)has developed rapidly in key technologies such as autonomous control and navigation positioning,the operational capability of a single vehicle is limited.For complex tasks with wide range and high difficulty,it is often necessary to coordinate the formation of UUV to fulfill the task requirements.Compared with single UUV,UUV formation has the advantages of high efficiency,adaptability and redundancy.However,the uncertainty of underwater environment makes it more difficult to design and implement UUV formation coordinated control system,so this paper has important theoretical research and engineering application value.In this paper,the problem of UUV formation coordinated control under weak communication conditions and complex marine environment is studied in depth.The main research contents are as follows,Firstly,the architecture of distributed control system for UUV formation system is constructed.Each vehicle carries out mission planning and coordinated control according to the mission and the environment,and communicates with other vehicles through communication system.The communication realationship between the vehicles is described by graph theory.Concerning about the complex dynamic characteristics of UUV model,based on the differential manifold and the Lie derivative,the second-order integral model of the UUV is obtained by precise feedback linearization method.The simulation system of multi-UUV formation system is established by using the complex dynamic model of the vehicle,so that the simulation system can simulate the real system structure as far as possible that makes the simulation be reliable and effective.Secondly,concerning about the problem of limited communication bandwidth and time delay in the multi-UUV formation system,a formation control method based on the leader-follower method is designed.Concerning about the problem of limited communication bandwidth,a virtual vehicle is constructed to obtain the reference velocity information and position information needed for follower tracking control only by using the position information of the leader.Only the position information is transmitted between vehicles,that reduces the amount of communication data.Concerning about the problem of communication delay between vehicles,formation coordination controllers are designed based on the consensus control theory in the case of with communication delay and without communication delay.The validity and stability of the formation system are analyzed by using Lyapunov-Krasovskii theorem,and the sufficient conditions to ensure the stable convergence of the multi-UUV system are obtained.Finally,the simulation results show that the formation system can achieve formation coordination only by the position information of the leader in the case of with communication delay and without communication delay.Thirdly,concerning about the problem that multi-UUV system may encounter obstacles when performing tasks in formation,two different formation control methods of coordinated obstacle avoidance and collision avoidance are proposed.Firstly,the obstacle avoidance and collision avoidance formation control method without a leader is considered.In this case,each vehicle in the multi-UUV formation has the ability to detect and avoid obstacles.When obstacles are detected,obstacle avoidance and collision avoidance control will be carried out while maintaining the desired trajectory.Then considering the case of with a leader,the formation coordination obstacle avoidance control is divided into online planning layer and coordinated tracking layer of hierarchical control.The online planning layer designs a virtual vehicle based on the desired trajectory and the obstacle information to obtain the reference path to avoid obstacles.The coordination tracking layer is designed to track the safe trajectory planned by the leader,and achieves the cooperative obstacle avoidance of the formation system.In the coordination tracking layer,the case of variable topology is considered,and the corresponding coordination controllers are designed for the switching topology which can maintain strong connectivity and can not maintain strong connectivity.Finally,concerning about the collision avoidance of multi-UUV formation system,the formation coordination control with prescribed performance is proposed.Firstly,the formation control method is designed based on the leader-follower method,which decomposes the multi-UUV system into n-1 series sub-formation consist of two vehicles,so that each vehicle except the global leader has a leader,and the follower is the leader of the next sub-formation.The collision avoidance problem is transformed into a state-constrained problem,and a time-varying performance function is proposed to describe the constrained state error,so that the system error can be constrained within a designed time-varying boundary within a specified time,thus achieving the desired transient and steady-state performance of the prescribed formation tracking error.By using the fast terminal sliding mode design method to select the prescribed performance function,the tracking error of formation system can reach the prescribed residual set within a specified time.Furthermore,concerning about the time-varying boundary conditions obtained by the prescribed performance constraints,a tracking controller is designed by combining the backstepping method with the barrier Lyapunov function,so that the tracking error can be stabilized within the designed time-varying boundary,which means the formation system can avoid collision while maintaining the formation.