Ship Course Control Based On Sliding Mode Variable Structure

With the development of shipping,the ship had begun to develop intelligently and large-scale,so the research on ship course control became more important.The sliding mode variable structure control had the characteristics of being independent of object parameters and disturbances.And its design process was simple,high efficiency control,well suited for the design ship course.This paper explored the selection of approach law,chatter suppression,and the improvement of convergence rate in sliding mode variable structure control methods.Finally,a combined double-power approach law was proposed.And the first-order ship course controller was designed by combining the iterative method and the combined double-power approach law.In addition,considering that the ship's first-order mathematical model had the problem of inaccurate description of the ship's motion characteristics.the ship's second-order nonlinear mathematical model was used to design the course controller.It introduced ADRC technology into designing the controller for solving the problem of estimating external unknown disturbances.The details were as follows:(1)In the sliding mode variable structure control method,the selection of the approaching law had a great influence on the approaching rate of the control system's moving points,and to some extent affected the chattering of the control system.Therefore,this paper compared the fast approach law with the double power approach law.The convergence time of the two approaching laws was calculated by mathematical methods.Finally,a combined double-power approach law was proposed on the premise of comparing the convergence time of the two approaching laws.The experimental resulted verify that the convergence law had a faster convergence rate and less chattering in the approach phase.(2)The first-order K-T mathematical model of the ship was used to design the course controller.However,the unknown items in the mathematical model would make the control system change from stable to divergent.Therefore,when designing the controller,the unknown items would generally be estimated and compensated,but it was bound to increase the design difficulty.To this end,the iterative sliding mode method was adopted in this paper to avoid the estimation and compensation of unknown interference items,which simplified the design of the control system.The design of the control law introduced a combined double-power approach law to improve the control effect of the controller and reduce the chattering.(3)The experimental verification results of the ship course controller showed that the parameter selection of the approach law affected the control effect of the control system,especially the approach speed of the control object.Therefore,in this paper,RBF neural network was used to estimate the parameters of the approach law online,so that the parameters of the approach law were kept in the best state at all times,and the approach speed of the controller was improved to optimize the effect.(4)Considering that the ship's first-order K-T motion mathematical model was a simple model,its description of the ship's motion was not accurate enough.Therefore,in the fourth chapter of this paper,a more accurate second-order K-T motion mathematical model was used to design the controller.In the design of the second-order nonlinear course controller,the auto-disturbance sliding mode control method was used to estimate and compensate the external disturbances and unknown disturbances of the system,making the course controller more in line with the requirements of practical applications.