Finite-time Trajectory Tracking Control Of Vessels Under Uncertain Disturbance

To solve the finite-time trajectory tracking problem of underactuated surface vessels which are influenced by dynamic uncertainties,external unknown time-varying disturbances and communication resources are limited.By combining the existing trajectory tracking control schemes and engineering requirements in actual sailing,a variety of finite-time control schemes are designed for the tracking system of underactuated vessels.Improve the tracking accuracy of the vessels,so that the tracking task can be completed safely and efficiently.Considering that the underactuated surface vessels will inevitably encounter unknown time-varying disturbances in the actual sailing.By means of coordinate transformation and norm calculation,the virtual control of the surge and sway dynamic systems is transformed to solve the problem of underactuating.By designing an adaptive law to approach the upper bound of the external time-varying disturbance,combined with the backstepping method and finite-time control theory,an adaptive finite-time trajectory tracking control scheme of underactuated surface vessels under uncertain disturbance is designed.Compared with the traditional scheme,the introduction of finite-time theory greatly increases the tracking accuracy of the vessels and the convergence speed of the system error.Then,considering the constraints of communication resources,an eventtriggered mechanism with a fixed threshold is introduced,and an event-triggered underactuated vessels adaptive finite-time trajectory tracking control scheme is designed.It not only ensures the high-precision tracking effect,but also saves computing resources and reduces the wear of the actuator.To solve the problem of the dynamic uncertainty of the vessels and the unknown time-varying interference of the outside world in the process of trajectory tracking.Combined with adaptive technology,the composite uncertain vector synthesized by uncertain parameters and external disturbances is converted into a linear parameterized form.Then,based on the backstepping design framework,a robust adaptive finite-time trajectory tracking control scheme for underactuated vessels is designed considering dynamic uncertainty.Furthermore,considering the limitation of communication resources,and in order to further extend the triggering time interval on the basis of the fixed threshold triggering scheme,a relative threshold event triggering mechanism is introduced.Based on this,an event-triggered robust adaptive finite-time trajectory tracking control scheme for underactuated surface vessels is designed.Considering that the vessels is affected by dynamic uncertainty and unknown external disturbance,to solve the conservative problem caused by the adaptive method in the control scheme approximating the uncertainty term.By use the neural networks to reconstruct the dynamic uncertainty of the vessels,and an adaptive law is designed to approximate the upper bound of external disturbance.Then,the control framework is designed by the method of backstepping,and an adaptive neural network finite-time trajectory tracking control scheme for underactuated vessels is designed according to the finite-time control theory.The introduction of neural networks technology further improves the tracking accuracy of the system.Furthermore,considering the limitation of communication resources in actual sailing,a relative threshold event-triggered strategy is introduced into the design of the control scheme,and an event-triggered underactuated surface vessels adaptive neural networks finite-time trajectory tracking control scheme is designed.Compared with the fixed threshold triggering scheme,the relative threshold further prolongs the triggering time and ensures the tracking accuracy.The Lyapunov stability theory provides a strict stability proof for the finite-time trajectory tracking control scheme designed above.All signals of tracking system of finite-time trajectory tracking control schemes developed are bounded,and the underactuated surface vessels can track the desired trajectory in finite-time.A ship model is selected as the object of simulation verification,and the simulation program is built by MATLAB.The simulation results show that the finite-time trajectory tracking control scheme in this paper can effectively solve the problems of dynamic uncertainty,external unknown time-varying disturbances and the limitation of communication resources.