Research On Autonomous Navigation Method Of Unmanned Surface Vehicle In Complex Dynamic Environment

With the rapid development of unmanned technology and the increasing demand for ocean development,unmanned surface vehicle(USV)has attracted more and more researchers’ attention and gradually becomes a research hotspot in many countries.Autonomous navigation technology is one of the key technologies in the field of USV,and it is also the embodiment of the intelligent level of USV.This paper focuses on the autonomous navigation method of unmanned craft in complex dynamic environment and carries out the following research.(1)The hardware system composition of USV is introduced and the autonomous navigation software system of USV is designed.In the design of software system,the global positioning module includes data preprocessing and coordinate system transformation;The environment perception module includes global environment perception based on Automatic Identification System(AIS)and local environment perception based on lidar;The communication module based on ROS uses the ROS framework to separate the message release and navigation control program,which is more convenient for the management of functional software.(2)Aiming at the path planning problem of USV in complex dynamic environment,a path planning method based on improved RRT*-Smart(RTSNew)is designed.Firstly,the sampling mode of nodes is optimized:nodes are sampled in the polar coordinate system with USV as the origin,an elliptical sampling range constraint is adopted to avoid invalid sampling,and a historical path buffer pool is used to make full use of the historical path;Secondly,the expansion mode of nodes is improved: time information is added to each node to realize dynamic collision detection and the angle constraint is added in expansion of nodes to ensure smooth path;Finally,virtual obstacles are designed to mobile obstacle ships to make the planned path comply with International Regulations for Preventing Collisions at Sea(COLREGs).Based on VREP platform,the USV navigation simulation experiments and comparative experiments are carried out.The results show that RTSNew performs better in planning efficiency,path optimization and path security than traditional methods in complex dynamic environment with multi-obstacle ships.(3)Aiming at the problem of path tracking control of USV in complex dynamic environment,a path tracking control method is proposed,which is based on improved line-ofsight guidance law and PID control with amplitude limitation.Firstly,to avoid the limitation of fixed forward-looking distance in traditional LOS method,a variable forward-looking distance LOS guidance law based on moving circle is designed,which changes the forward-looking distance in real time according to the relative position relationship between moving circle and desired path;Secondly,the path tracking method based on PID control with amplitude limitation is designed.In this control method,two PI controllers are used to control the basic control quantity and left-right deviation of the propeller respectively to realize the speed and heading control;Finally,simulation experiments are carried out to compare the path tracking effect of this method with traditional LOS method.Results show the advantages of this method from the aspects of tracking accuracy,convergence speed and stability.In addition,the control method has been successfully applied to the USV race and achieved excellent results.