Research On Path Planning And Trajectory Tracking Control Of Underactuated Unmanned Surface Vehicle

Unmanned surface vehicles(USVs)are widely used in inland and offshore scenes to perform unmanned tasks,such as water quality sampling,island reef mapping and so on,due to their small size,shallow draft and multiple functions.In this paper,the "Jinghai 8-b" USV of the research group is taken as the research object,and the path point tracking task of USV is studied.Aiming at the problems of large tracking error and slow error convergence of USV in sharp turns and other extreme scenes,a path planning method based on LOS(Line-of-Sight)guidance and generalized predictive control(GPC)and a trajectory tracking method based on sliding mode control(SMC)are proposed.LOS-GPC-SMC control strategy is proposed by combining the two methods to realize the path tracking control of USV.On this basis,the formation control of the USVs is studied.The follower independent control method is adopted,and the formation control problem is transformed into a trajectory tracking problem through formation control kinematics.Finally,the formation control of the leader-follower was realized.The main contents of this paper are as follows:In order to simplify the control difficulty in USV motion modeling,considering the external interference,an unmanned boat hydrodynamic model is established,which only considers the motions of the USV in the three directions of surge,sway and yaw.In order to make the generated virtual trajectory contain the maneuvering performance constraints of the hull,the Nomoto model of "Jinghai 8-b" USV is established.In addition,because the "Jinghai 8-b" USV is driven by two propellers,the thrust is generated by the two propellers,and the bow rotation is realized by the difference between the two propellers.In order to pave the way for subsequent simulation,the mathematical expression between the forward thrust,the bow rotation torque and the throttle value of the two propellers is established.In the aspect of task path planning,a virtual trajectory generation strategy based on LOS guidance and GPC algorithm(LOS-GPC method)is proposed.Through LOS guidance algorithm,the path point tracking problem is converted into heading tracking problem.Then the obtained virtual heading is input to the virtual ship designed by GPC algorithm of the controller,thus generating a virtual trajectory.Finally,the feasibility of the proposed method was proved by simulation experiments.In the aspect of trajectory tracking control,aiming at the trajectory tracking problem of USV under the condition of uncertain parameters and external disturbances such as wind waves and currents,the longitudinal and transverse virtual control laws in the kinematic loop are designed to convert the trajectory tracking problem into the speed tracking problem.Then the longitudinal speed controller and the heading controller of the unmanned craft are designed to track the virtual control law by adopting the sliding mode control method.In addition,in order to effectively solve the state jitter problem existing in the sliding mode control law,a new adaptive switching law is designed to reduce the jitter of the system.Finally,the effectiveness of the proposed method was verified by simulation experiments.In the application of formation control,aiming at the formation control problem in the environment disturbance and parameter perturbation scenarios,the leader-follower formation control method is proposed to transform the formation control problem into a tracking control problem in combination with formation kinematics.For the leader,the expected path is given by the staff in the form of points,and then a virtual trajectory is generated in the form of LOS-GPC,which contains the maneuvering performance constraints of unmanned craft.The controller of the pilot is designed by the proposed sliding mode control method,and then the virtual trajectory is tracked.For the follower,its expected trajectory is generated by combining the navigation trajectory of the leader with the relative position.The controller of the follower is designed by using sliding mode control method.Finally,the feasibility of the proposed method was proved by simulation experiments.Through the implementation of path point tracking control and the application of formation control cases,it is shown that the proposed LOS-GPC-SMC control strategy can effectively realize path point tracking control,and the proposed sliding mode control scheme can better realize path tracking in the presence of parameter perturbation and external interference,and the combination of the proposed path planning method and sliding mode control scheme with formation kinematics can well realize formation motion control.