Research On USV Sliding Mode Control And Path Tracking Based On Los Method

Unmanned Surface Vessel(USV),also known as Surface Robot,is a surface ship capable of unmanned operation.Nowadays,all countries are actively engaged in research.They are well aware of the importance of the research on unmanned surface craft in national military or civil fields,and help human beings to accomplish some tasks that are not suitable for human participation.Therefore,the research work on unmanned surface craft is very worthwhile.This paper focuses on the design of sliding mode controller and path tracking for USV.On the basis of LOS,the expectation of position in path tracking is transformed into the expectation of heading,so that the process of path tracking can be realized only by controlling the heading angle.Firstly,the mathematical modeling of USV is realized.For the convenience of research,the model needs to be simplified.Then,considering the influence of ocean currents,the final model form is obtained.Then a simulation experiment is carried out to verify the availability of the model.The sliding mode controller is designed to solve the problems of model coupling,incompleteness of constraints,uncertainty of model parameters,ocean current effect,sliding mode chattering,control input saturation and tracking accuracy in under-actuated USV path tracking control.Under objective conditions,the control system can achieve better performance.Good tracking effect to provide a basis.Secondly,the guidance system is studied.In the path tracking of USV,the LOS method is used to obtain the real-time expected heading.In the case of ocean current disturbance,the traditional line-of-sight guidance method will cause the system to have the problem of steady-state path tracking error.A concept of side slip angle is added here to correct the period obtained by LOS method.Looking forward to reduce tracking error and improve tracking accuracy.Thirdly,the control theory of a decoupling method is adopted.Firstly,the error equation is established based on LOS method,and the tangential velocity on the tracking path is input to solve the problem of under actuation of USV.Then decoupled into three subsystems: speed control,position control and heading angle control.Sliding mode control is designed considering the influence of ocean currents.Finally,the designed sliding mode controller is simulated and verified.Finally,in view of the chattering effect of sliding mode control,an adaptive law is designed under the premise of Lyapunov stability theory in horizontal path tracking control,which can change the thickness of sliding mode boundary layer and switching gain,so as to reduce the chattering effect and improve the tracking accuracy.In this paper,a compensation mechanism is added to the propeller model to limit the control input.Then the stability of the designed controller is analyzed by using the Lyapunov stability theory.In the simulation experiment,the sliding mode controller and the adaptive sliding mode controller are compared under the disturbance of ocean current and model,which verifies the correctness of the designed control method in USV path tracking.The adaptive sliding mode control algorithm proposed in this paper for USV reduces the impact of chattering to a certain extent.Saturated input of the system has been solved to a certain extent.It can improve the accuracy of path tracking under the stable state of the system.Under the disturbance of ocean current and model,the control can satisfy the objective conditions of engineering application.The validity of the designed controller is fully proved.