Research On Adaptive Robust Trajectory Tracking Control Of Underactuated Ship

The trajectory tracking of ships is a process that the ship enters the preplanned route from the initial position,and finally reaches the destination along this route during navigation.Underactuated ships are surface vessels whose number of their control inputs is less than the dimension of freedom.At present,underactuated ships play an important role in maritime operations,and have made significant contributions to the maritime trade.In addition,they have been widely used in the military field and other projects.Since the operational conditions and the ocean environment are constantly changing,there exist obvious uncertainties of the ship’s dynamics and the disturbances.The velocities of the ship may also be unmeasured.Because of the inherent physical limitation of the ship propulsion system,the control force and torque produced by it could be constrained.Additionally,considering the safety of navigation,the ship’s outputs need to be constrained while the ship enters the restricted sea area.Therefore,the research on trajectory tracking control of urideractuated ships has important theoretical significance and practical application value.Firstly,the motion mathematical model of an underactuated ship is established in this thesis.Then,for the trajectory tracking control problem of the underactuated ship subjected to unknown time-varying disturbances,herein,the adaptive law is designed by applying the adaptive technology to estimate the bounds of unknown time-varying disturbances.Based on the above,the trajectory tracking control law for the underactuated ship is designed incorporating the output redefinition method and the command filtered backstepping approach.Furthermore,under the condition of unavailable ship velocities,a sliding mode state observer is designed to estimate the ship’s velocities based on the actual trajectory and control input of the ship,and the trajectory tracking control law for the underactuated ship is designed incorporating the output redefinition method,the adaptive technology and the command filtered backstepping approach.Under the condition of inputs saturation,unknown time-varying disturbances and unavailable ship velocities,an auxiliary design system is designed to address the effect of inputs saturation,a sliding mode state observer is designed to estimate the ship’s velocities,and the trajectory tracking control law for the underactuated ship is designed incorporating the output redefinition method,the adaptive technology and the command filtered backstepping approach.Additionally,under the condition of ship’s dynamics uncertainties,unknown time-varying disturbances and unavailable ship velocities,an extended state observer is designed to estimate the compound disturbances induced by ship dynamics uncertainties,unknown time-varying disturbances and coupling between the ship motion state variables,and ship velocities based on he actual trajectory and control input of the ship,and the trajectory tracking control law for the underactuated ship is designed incorporating the output redefinition method and dynamic inversion control approach.Furthermore,under the condition of outputs constraint,the error transformation method is employed to deal with outputs constraint,an extended state observer is designed to estimate the compound disturbances and ship velocities,and the trajectory tracking control law for the underactuated ship is designed incorporating the output redefinition method and dynamic inversion control approach.The simulations of the above trajectory tracking control laws are carried out using the Matlab/Simulink toolbox on the underactuated ship.The simulation results show the effectiveness of the designed trajectory tracking control laws of underactuated ship.