Event-triggered Based Path Following Control Of Marine Surface Vessel

With the rapid development of Marine industry in China,more and more attention has been paid to the research of more accurate ship motion control technology,especially ship path following control.Therefore,through the in-depth study and analysis of the research results of ship path following control at home and abroad,the research hotspots arid difficulties in the current ship path following field have been known,Because the traditional ship path following control mostly adopts the control strategy based on periodicity,but this control strategy has a great impact on energy consumption and mechanical wear of propeller and controller.Therefore,an event-triggered control strategy which can reduce energy consumption and mechanical loss of the controller is applied in this paper,and a path following control method based on event-triggered mechanism is designed.Then the method is tested in MATLAB simulation.Firstly,a neural network algorithm based on fixed threshold event-triggered mechanism is designed for underactuated vessel with unknown model dynamics.This method takes use of radial basis function neural network to solve the problem of unknown dynamics in the system model of underactuated vessel,at the same time,the update times of the controller is reduced by event-triggered strategy.Secondly,a neural network event-triggered control algorithm based on finite-time convergence is designed for underactuated vessel with unknown model dynamics.While solving the unknown dynamics of ship model,a fixed threshold event-triggered condition based on finite-time convergence and a relative threshold event-triggered condition based on finite-time convergence are designed.The theoretical analysis through Lyapunov method shows that the tracking error can converge to zero in a finite time and the Zeno phenomenon can be avoided.It can be seen from the simulation results that compared with the fixed threshold event-triggered control method,the relative threshold event-triggered control method can effectively reduce the update frequency of the controller and the loss of the actuator.Finally,a sliding mode relative threshold event-triggered control method based on improved saturation function is proposed for the path following control of fully-actuated vessel.In order to meet the requirement of the system for enhance robustness,a sliding mode controller with improved approach law of saturation function is proposed,which enhances the robustness of the system and reduces the chattering phenomenon caused by frequent switching of sliding mode surface in traditional sliding mode control,so as to obtain good control performance.By combining with the improved sliding mode controller with the relative threshold event-triggered condition,the update frequency of the controller and the loss of the actuator are greatly reduced.The theoretical analysis through Lyapunov method shows that the tracking error of the system converges exponentially to a compact set.Finally,the effectiveness of the algorithm is verified by MATLAB simulation.