Research On Leader-Follower Formation Control And Obstacle Avoidance Of Multi-UUVs For Formation Voyaging

With improvements of ocean area expansibility,environmental complexity and task diversity of Unmanned Underwater Vehicle(UUV)mission,the collaborative operation by constructing and utilizing multi UUV system has received increasing attention,and coordinate control technology has become a hot research field now.Where,formation capability is the basis for constructing,maintaining and optimizing multi UUV system and its collaborative applications.Formation control,as a supporting and key technology,has been pushed to the forefront of multi UUV coordinate control technical field.Taking the leader-follower UUV formation as the research object,three core problems of formation keeping,formation switching and formation obstacle avoidance involved in voyage scenario are researched in this paper.focusing on the unique difficulties and practical challenges faced by UUV formation,such as acoustic information delay,inaccurate navigation and acoustic detection uncertainty,innovative exploration and research of the leader-follower formation control methods are present in this paper,and the verification of relevant lake experiments and actual environment simulations is completed.Due to the characteristics of low bandwidth and large delay of acoustic communication,traditional pure acoustic communication means and decentralized interaction topology of UUV formation have the problems of large traffic and multiple frequencies,which eventually leads to the increase of information sharing delay within the UUV formation and seriously affects the effect of formation control.Firstly,a communication-measurement joint cluster head acoustic information interaction topology is proposed and its implementation scheme is present in this paper.The information obtained for UUV formation is realized by comprehensively using two means of acoustic communication and acoustic measurement.Meanwhile,The information shared among UUV formation is realized by the way of collection and distribution through a information cluster head UUV.The proposed information topology greatly improves the efficiency of acoustic interaction between UUVs and reduces the delay of information sharing.In addition to the time delay of acoustic information interaction,the inaccuracy of absolute position caused by navigation divergence is also the main problem causing poor control effect of formation keeping.So,a leader-follower formation keeping control method based on relative position prediction is proposed in this paper.Its core ideas are as follows:first,the formation keeping control of UUV formation is realized only based on the relative position information without relying on the absolute position information;Second,according to the time delay characteristics of the acoustic information topology,the relative position information is predicted to compensate for the time delay.Therefore,the formation keeping control law of follower UUV is designed based on Lyapunov stability theory and back-stepping method firstly.Secondly,relative position prediction method based on receding horizon is proposed,and the prediction information is used in the control law to effectively improve the effect of formation keeping control under information delay.According to the demand of UUV formation voyaging scenario,the problem of dynamic formation switching is researched.The core of this problem is how to avoid the collision between UUVs.However,The acoustic interaction information delay and inaccurate position increase the difficulty of anti-collision between UUVs.So,a leader-follower and artificial potential field combined formation switching control method is proposed using null space based(NSB)mechanism.In this method,the artificial potential field is used to realize the anti-collision control between UUVs,and the leader-follower formation keeping is used to increase the formation rigid body constraint and further reduce the collision risk.At the same time,in order to avoid the conflict between the two behaviors,a combined formation switching control law based on null space conflict resolution is designed,which makes the UUV formation switching have the advantages of good rigid constraints and fast anti-collision response.The obstacle avoidance of UUV formation is faced with the double difficulties caused by sonar detection uncertainty and formation scale constraints.In addition,this paper studies a more realistic UUV formation avoidance scenario,that is,only the leader UUV is equipped with avoidance sonar and has avoidance capability.Then,the UUV formation needs to realize obstacle avoidance only under the guidance of the leader UUV.Therefore,a formation avoidance method based on scale derived vector field histogram integrated with formation switching decision is proposed,which is solved from three aspects:the representation of formation obstacle environment,the generation of formation avoidance behavior and the adaptability of formation avoidance in different obstacle environments.Finally,the whole obstacle avoidance ability of leader-follower UUV formation is realized,which can only limited to leader UUV guidance and can adaptively formation switching in the avoidance process.The simulation verification under different conditions for the above leader-follower UUV formation keeping control method,formation switching control method and formation obstacle avoidance method is carried out in this paper.In addition,the leader-follower UUV formation keeping control based is verified by lake experiments based on five UUV platforms,as well as the formation avoidance method is simulated based on the real island obstacle environment.