Research On Path Following Of Unmanned Surface Vehicle Based On Line-of-sight Guidance And Adaptive Sliding Mode Control

The Unmanned Surface Vehicle(USV)is widely used in all kinds of water operation tasks with its characteristics of accurate,fast and smooth following of desired path,but with the complexity and variability of operating environment and tasks,it has prompted the exploration of the USV path following methods to become a hot spot.In this paper,I investigate the underactuated USV path following problem in the presence of unknown time-varying wind and wave flow environmental perturbations and model uncertainty terms,the specific studies are as follows:(1)To address the arbitrary parametric path following problem of USV under the influence of unknown time-varying currents,a composite line-of-sight guidance law is proposed to solve the compensation problem of currents and sideslip angle under the unknown currents perturbation.That is,considering the influence of the sea current on the guidance,the dynamic equation of the path following error with the introduction of the velocity component of the sea current is established based on the Serret-Frenet coordinate system,the downscaled dilated state observer is designed to realize the simultaneous estimation of the time-varying sea current and the time-varying sideslip angle,and the virtual control input is proposed to compensate the sea current perturbation,while the time-varying forward-looking distance is designed to improve the dynamic convergence performance of the system.The longitudinal velocity and heading controllers are designed based on Lyapunov’s stability theorem and the backstepping method for verifying the composite line-of-sight guidance effect,and it is demonstrated that all errors of the closed-loop system are bounded.The simulation results show that the composite line-of-sight guidance proposed in this paper has a good guidance effect on both Cyber Ship II USV and Test USV numerical model,which can effectively estimate and compensate the time-varying currents and sideslip angles,and guarantee the USV to converge to the desired path quickly and stably.(2)For the arbitrary parametric path following problem of the USV with wind and wave flow factors disturbance and internal model uncertainty,based on the composite line-of-sight guidance law,the adaptive sliding mode controller is proposed to approximate the disturbance and uncertainty terms to induce the smooth switching of the sliding mode.That is,the upper bound of the perturbation such as wind and waves and the uncertainty term of the model are approximated based on the adaptive method and the minimum parameter learning method,respectively,and the adaptive gain is designed to reduce the sliding mode jitter and improve the system robustness.To address the problem of computational complexity of the higher order derivation of the desired heading guidance law in the heading controller,a third-order differential tracker is designed to solve the differential term of the guidance law.The cascade stability of the composite line-of-sight guidance and adaptive sliding mode controller proposed in this paper is then demonstrated.The simulation again verifies the applicability of the composite line-of-sight guidance by the Cyber Ship II USV model and the Test USV model,and demonstrates that the adaptive sliding mode controller performs better than the isokinetic convergence sliding mode controller,and is effective in approximating the upper bound of disturbances such as wind and waves and model uncertainty terms,which can improve the path following control accuracy of the USV.(3)In order to verify the correctness of the Test USV model,the Test USV longitudinal thrust and its corresponding test steady-state longitudinal velocity data table are established by building and commissioning the Test USV,conducting thrust test and direct flight acceleration test,and comparing and analyzing the simulated steady-state longitudinal velocity obtained by direct flight simulation under the same longitudinal thrust to verify the correctness of the Test USV model.In summary,this paper proposes a composite line-of-sight guidance law to estimate and compensate for time-varying sideslip angle and time-varying current disturbances,and designs an adaptive sliding mode controller that approximates the upper bound of wind and wave disturbances and model uncertainties for the underactuated USV path following problem affected by unknown time-varying wind and wave current disturbances and the existence of model uncertainties.After simulation and comparison analysis,the proposed guidance and control method is effective and feasible,which improves the accuracy,rapidity and smoothness of the underactuated USV path following.