Research On Trajectory Tracking Control For Fully Actuated Ship

Fully actuated trajectory tracking ships are usually employed in important ocean engineering operations,such as marine oil gas exploration,offshore cargo transportation,undersea pipeline bedding owing to their flexible maneuverability and high safety.The characteristics of ocean engineering are that ships are required to move precisely according to the prior route to ensure safe completion of the operations.Because of the ships with highly nonlinear and strong coupling are unavoidably subjected to external unknown marine environment disturbances.The design of high-precision trajectory tracking control of the ship is facing severe challenges.Therefore,it is of great academic significance and engineering application value to study the trajectory tracking control of fully actuated ships.The main research contents of this paper are as follows:According to the motion characteristics of the ship,the motion mathematical model of the fully actuated ship is derived.Firstly,the north-east-down reference frame and the body-fixed reference frame are established to describe the position,attitude and other state information of the ship.Then,from the analysis perspective of kinematics and dynamics characteristics,the kinematics model and dynamics model of the six degree of freedom(6-DOF)fully actuated ship are established by coordinate transformation and Newton Euler equation respectively.Finally,the mathematical model of ship motion is simplified for the trajectory tracking control task mainly studied in this paper,and the marine environmental disturbance is analyzed.The 3-DOF fully actuated ship motion mathematical model with external unknown time-varying environmental disturbances and model parameter uncertainty is established,and the expressions in different reference frame are given respectively.For the trajectory tracking control problem of fully actuated ship with external unknown time-varying environmental disturbances and model parameter uncertainty.Firstly,the second order error equation of 3-DOF fully actuated ship trajectory tracking control model is given.Then,the nonlinear disturbance observer is designed to estimate and compensate the unknown compound disturbances composed of external disturbance and model parameter uncertainty.Finally,the state equation of the system is established,and the trajectory tracking controller is designed with the idea of backstepping and Lyapunov function to improve the tracking performance of the control system.The nonlinear disturbance observer has common estimation of high frequency time-varying disturbances,the trajectory tracking control problem of fully actuated ship with model parameter uncertainty is further studied.Firstly,the disturbance observer is designed to estimate high frequency disturbance using the approximation ability of the neural network.Then,the estimated numerical value is feedback to the parametric controller,and the unknown disturbances of the system are compensated in the form of a compensation controller.Finally,in order to improve the performance of the system and restrain the influence of high nonlinearity and strong coupling on the trajectory tracking control,the direct parameteric approach is used to design the controller,which flexibly transforms the trajectory tracking problem into the stabilization problem of the error system.The effectiveness of the controller designed in this paper is verified,simulations of different trajectories based on an engineering supply ship are carried out.The results show that the designed observer can better estimate the time-varying disturbances of the external unknown environment and the model parameter uncertainty,and controller outputs are reasonable and effective,the control objectives can be achieved.