Research On Autonomous Berthing Control Method Of Under-actuated Unmanned Surface Vehicle

Nowadays,human beings attach great importance to the development of the ocean.As the representative of smart ships,under-actuated unmanned surface vehicle have been paid more and more attention to.Precision autonomous berthing technology can avoid many accidents caused by inappropriate maneuvering and reduce the loss of manpower and material resources during the berthing process.Therefore,it is important to study the problem of under-driven autonomous berthing for the development of smart ships in China..This article has carried out the research on the autonomous berthing control method of the under-actuated unmanned surface vehicle,and divided the whole berthing problem into three parts,namely berthing path planning,berthing path tracking and berthing stabilization control.The specific work of this article mainly includes the following aspects:(1)Aiming at the problem of berthing path planning,a berthing path planning algorithm based on improved artificial potential field method is proposed.Firstly,the grid method is used to build the model of the berthing port map.Secondly,according to the problems encountered in the berthing scenario,such as unreachable targets,excessive gravity,etc.,the artificial potential field method,the calculation method of total repulsion,the calculation formula of gravity and repulsion.The artificial potential field method is more suitable for the planning of berthing paths in the port,and the redundant path reduction and optimization of the planned path.Finally,the simulation experiment verifies that the algorithm can realize the planning of the berthing path of the unmanned surface vehicle in the port.(2)Aiming at the berthing path tracking problem,the berthing path tracking controller based on Fuzzy-LOS is proposed.First,the line-of-sight guidance algorithm is improved in the guidance part.Combining it with fuzzy control enables the forward-looking distance to be adaptively changed according to the current operating state of the unmanned surface vehicle,so that the unmanned surface vehicle is farther away from the desired path.Or when it is disturbed,it can converge to the route more quickly.Secondly,in the control part,a longitudinal speed control law and a heading control law based on sliding mode variable structure control are designed,which can complete the tracking control task of the unmanned surface vehicle according to the signal given by the guidance system,and prove the stability of the system .Finally,simulation experiments verify the effectiveness of the berthing path tracking controller designed in this chapter.(3)Aiming at the final step of the berthing task,the problem of berthing stabilization,a fractional-order back-step sliding mode berthing stabilization controller based on disturbance observer is proposed.Firstly,for the disturbance received in the process of berthing stabilization,a disturbance observer is designed to estimate the disturbance values and perform feedforward compensation for the control system.Secondly,the three-degree-of-freedom model of the unmanned surface vehicle with interference terms is transformed into two cascade systems.The fractional-order calculus is introduced into the traditional sliding mode to improve the integralorder calculus sliding-mode surface.For the transformed two subsystems,a fractional-order back-step sliding-mode berthing stabilization controller based on disturbance observer is introduced The boundary layer suppresses sliding mode jitter and proves the stability of the control system.Finally,simulation experiments verify the effectiveness of the berthing stabilization controller designed.