Research On Fixed-Time Trajectory Tracking Control Methods For Fully Actuated Vessels

In recent years,with the development of the marine economy and the increasing attention to the maritime status,many countries have steadily increased the efforts to develop marine resources and preserve national marine rights and interests.Therefore,the vessel,as the important marine transport vehicle,has been continuously developed.Among these different types of vessels,the fully actuated marine surface vessel,due to the existence of the independent transverse propulsion device,can efficiently achieve some ocean missions that require high maneuverability and safety,such as submarine pipeline laying,offshore oil and gas drilling and mine sweeping tasks,etc.,which all require the vessel precisely moving along the predefined trajectory.Thus,the higher control accuracy and faster real-time is necessary for the vessel trajectory tracking control.However,The fully actuated marine surface vessel has the characteristics of high non-linearity,strong coupling,hydrodynamic coefficient perturbations and inevitably influenced by unknown external ocean disturbances.These factors make the high performance trajectory tracking control design a challenging task.In this paper,the model uncertainties,unknown external disturbances,actuator input saturation constraints,tracking error output constraints,bounded system convergence time and unknown velocity measurements are taken into account in the trajectory tracking control.In order to obtain the control performance with fast convergence,high tracking accuracy and strong robustness,the problem of trajectory tracking control for marine surface vessel is studied mainly based on the finite-and fixed-time control theory.The specific research work includes the following aspects:(1)Aiming at the problem of trajectory tracking control for the marine surface vessel with model uncertainties,unknown external disturbances and tracking error constraint,an adaptive neural network-based trajectory tracking control method with the finite-time convergence time is proposed.Firstly,considering the difficult to obtain the accurate hydrodynamic coefficients,a radial basis function-based neural network approximator is desinged to online approximate the unknown hydrodynamic terms.Without the information of disturbance bounds,a nonlinear disturbance observer is proposed to further estimate and compensate the lumped disturbances consisting of the unknown disturbances and the approximation errors of the neural network.Secondly,in the framework of backstepping design,an adaptive neural network-based trajectory tracking controller with error constraints is designed by using the time-varying barrier function method and the finite-time stability theory.Moreover,a second-order command filter combining with an auxiliary dynamic system is adopted to obtain the time derivatives of the virtual control law,which can effectively avoid explosion of terms in the backstepping method.Then,the finite-time stability of the closed-loop system is proved by using the Lyapunov stability theory.Finally,the simulation results show that the proposed control strategy has faster convergence speed and higher control accuracy.(2)Aiming at the problem of fixed-time trajectory tracking control for the disturbed marine surface vessel with input saturation constraints,a terminal sliding mode-based fixed-time trajectory tracking control method is proposed.Firstly,to eliminate the influence of system initial states on the convergence time,a novel non-singular fixed-time fast terminal sliding surface is designed based on fixed-time stability theory,which can guarantee the sliding phase being quickly completed within fixed-time.Based on the homogeneous system theory,a practical fixed-time disturbance observer is designed to reconstruct the lumped disturbances within fixed-time.Then,combining with the designed disturbance observer,a non-singular fixed-time terminal sliding mode trajectory tracking controller is proposed,which can further improve the convergence performance and robustness of the system.Besides,the control input chattering phenomenon is also effectively reduced.In order to avoid the control singularity in the traditional terminal sliding mode control,a homogeneous integral terminal sliding mode-based fixed-time trajectory tracking controller is designed with the help of the fixed-time homogeneous system theory,integral sliding mode control and the designed anti-saturation compensator.Numerical simulations are presented to prove that the proposed control scheme has better control performance.(3)Aiming at the problem of fixed-time trajectory tracking control for the marine surface vessel with model uncertainties,unknown external disturbances,tracking error constraints and the requirement of the smooth and continuous control signals,a fixed-time trajectory tracking control method is proposed based on the extended adding a power integrator algorithm.First of all,the unknown upper bounds of the lumped disturbances are estimated by using the adaption technique,and an adaptive fixed-time trajectory tracking controller with smooth output signals is designed based on the extended adding a power integrator algorithm.Moreover,in order to further improve the robustness of the control system,a fixed-time exact robust disturbance observer is designed,which can ensure the disturbance estimation error convergence in fixed-time.By proposing an extended adding a power integrator algorithm with output constraints,a disturbance observer-based fixed-time trajectory tracking controller with error constraint is proposed for the marine surface vessel.Finally,the simulation results show that the proposed control scheme can provide faster convergence rate,stronger robustness and higher control accuracy for the trajectory tracking control of a vessel.(4)Aiming at the problem of fixed-time output feedback trajectory tracking control for the disturbed marine surface vessel with unavailable velocity measurments,tracking error constraints and input saturation constraints,an extended state observer-based fixed-time output feedback trajectory tracking control method is proposed.Firstly,a double power fixed-time extended state observer,which can simultaneously observe the velocity information and the total disturbances of a vessel within fixed-time,is proposed based on the homogeneous system theory and the Lyapunov stability analysis.The designed extended state observer can effectively improve the convergence rate of the observation errors and eliminate the influence of initial conditions on the observation performance.Subsequently,by designing an anti-saturation auxiliary dynamic system and combining the extended adding a power integrator algorithm with output constraints,an anti-saturation output feedback controller for the fixed-time trajectory tracking of a vessel is completed.Eventually,numerical simulations are presented to illustrate that the designed control strategy can effectively enhance the anti-saturation ability of the system,and has excellent observation and control performance.