Research On Path Planning And Obstacle Avoidance Technology Of Unmanned Surface Vehicle Formation

Unmanned Surface Vehicle(USV),as a surface platform with autonomous navigation and automatic operation capabilities,has the characteristics of low cost and strong environmental adaptability,and is widely applied in both civil and military fields.Path planning and obstacle avoidance are the key technologies to realize the intelligence of unmanned surface vehicles.Compared with a single unmanned surface vehicle,using a formation of multiple unmanned surface vehicles to collaborate and achieve common goals can improve efficiency and enhance fault tolerance.In this context,this paper studies related technologies and designed a path planning and obstacle avoidance algorithm of unmanned surface vehicle formation suitable for dynamic environment.The main work of the thesis is as follows:(1)Based on the reference coordinate system and the hydrodynamic theory,the general kinematics and dynamics model of the surface vehicle is established.And according to the plane motion characteristics of the under-actuated surface vehicle,ignoring the pitch,roll and heave,the simplified three degree-of-freedom(DOF)mathematical model including surge,sway and yaw is founded,which provides a mathematical foundation for subsequent algorithm design.(2)Design a global path planning algorithm based on grid environment modeling and improved A* algorithm.Firstly,dynamically change the search step length to improve the efficiency of the A* algorithm while carrying out a large scale searching.With reasonable parameters,the efficiency can be increased dozens of times.Then use the LOS method to extract the key nodes and apply the Dubins path to smooth process to eliminate the corners in the path,so that the generated path conforms to the motion constraints and safety requirements.The simulation results indicate that the improved A* algorithm can rapidly generate a safe and feasible path with high smoothness,and the performance of the algorithm is greatly improved compared with the existing algorithms.(3)Propose the dynamic artificial potential field based on the traditional artificial potential field,the relative velocity and global reference path are introduced to establish the velocity potential field and the guidance potential field,which improves the ability to avoid dynamic obstacles.And solved the unreachable problem and the local minimum problem of the artificial potential field method.The actual data is obtained by an unmanned surface vehicle equipped with radar and integrated navigation equipment,and a semi-physical simulation is carried out.The results prove that the algorithm can effectively avoid priori unknown obstacles while tracking the reference path as much as possible.(4)Aiming at the formation of three unmanned surface vehicles,use the leader-follower method to transform the formation control problem into the trajectory tracking problem.Then based on the Lyapunov stability principle,considering the uncertainty of the unmanned surface vehicle model parameters,the kinematics controller is designed to obtain the virtual control rate,and then the dynamic controller is designed using the sliding mode control(SMC)method,and the switching control rate is replaced by the saturation function to reduce the state chattering.The simulation results indicate that the control method can achieve effective tracking to the target trajectory.After that,introduce the virtual leader to design a hierarchical formation control method,which combines formation control with path planning and realizes formation maintenance,transformation and obstacle avoidance in a dynamic environment by switching between the follow mode and the obstacle avoidance mode.While maintaining the integrity of the formation,give each member of the formation autonomy.The simulation results in a dynamic environment indicate that the hierarchical method can realize autonomous path planning and obstacle avoidance of unmanned surface vehicle formation.