Research On Adaptive Trajectory Tracking Control Of Underactuated Surface Vessels

The development of modern shipping industry has posed higher requirements for ship motion control.Automated and intelligent ships can improve operational efficiency and reduce labor costs,and are gradually favored by the industry.An underactuated surface ship needs only two controllers to control its planar motion.Compared with a fully actuated ship,it can reduce the construction cost and the complexity of ship design.In addition,when any impeller is damaged or malfunctioning,the fully actuated ship degenerates to an underactuated system.Therefore,it is of great theoretical significance and practical engineering application value to study underactuated ships.However,there is no control force for the underactuated surface ship to control its lateral motion,and it can only be indirectly controlled by controlling the yaw motion.Thus,the design of the controller is very difficult.Moreover,ships sailing in open waters would inevitably be affected by environmental disturbances,this,coupled with the nonlinear,time varying characteristics of the ship’s dynamic model,brings larger challenges to the motion control of underactuated surface ships.Conventional surface ships are usually required to sail on the predefined route with a constant speed,but not strictly required to arrive at a given place at a given moment.However,for ships that need to perform some special operations,such as pipeline laying ships and underway replenishment ships,they need to be controlled in accordance with the desired trajectory.In these scenarios,they need to be controlled not only in yaw motion but also in longitudinal motion.Aiming at these practical requirements,this thesis studies the adaptive trajectory tracking control of underactuated surface ships,and focus is put on solving the uncertainty of the system and the adaptive compensation of the environmental disturbances.The main research outcomes are listed as follows.(1)The mathematical models of underactuated surface ships are constructed,including the simulation model and the controller design model.In this thesis,the equations of three-degree-of-freedom(3DOF)manoeuvring motion are systematically derived,and the models of hydrodynamic force acting on the hull,the rudder and the propeller are established to obtain a high-fidelity simulation model,where the dynamic characteristics and saturations of the actuators are considered.The modeling of common environmental forces,including wind load,wave load and ocean current load,is introduced in detail.Corresponding numerical simulation modules are established to test the response characteristics of the controlled ship under the environmental disturbances.(2)With the thrust of the propeller and the moment of the rudder as the control inputs,the controller design of trajectory tracking for the underactuated surface ship is studied.Based on the adaptive back-stepping technique,the trajectory tracking controller is designed for underactuated surface ships with known and unknown model parameters.Through the two stability functions dU and 3dz designed in this thesis,the control laws can be obtained indirectly,and then the global asymptotic stability of position tracking error can be guaranteed.Based on the designed trajectory tracking controller,an automatic berthing algorithm for an underactuated ship is constructed.Through the computer simulations,it is verified that the designed controller can accurately track the reference trajectory.(3)Taking the rudder angle and propeller revolution as the control inputs,the controller of trajectory tracking for the underactuated surface ship is designed.The control system is constructed as a cascade system composed of the guidance module and the control module.The guidance module is based on kinematics,while the control module is designed based on the simplified dynamic models.The guidance laws of the desired yaw angle and longitudinal velocity of straight-line trajectory tracking are derived,and the guidance strategy combining LOS(Line of Sight)and ILOS(Integral Line of Sight)is proposed,whose stability is proved.Based on the linear Nomoto model,a yaw tracking controller is designed by using sliding mode control(SMC)technology to control the yaw motion of the ship.Based on the extended state observer in active disturbance rejection control(ADRC),a state is extended to capture the modeling error and external disturbances of the system,and then feedforward compensation is made in the longitudinal velocity controller.(4)Study is also carried out on the problem that the rudder angle changes dramatically when there are wave disturbances.By establishing an appropriate wave model and combining Kalman filter technology,both the low-frequency and wave-frequency yaw motions are obtained in real time from the measured data which are polluted by noise.Further the controller is designed to compensate only for the low-frequency yaw motion induced by the low frequency wave force and steering,to avoid the wear and tear of the actuator when frequently steering.In this thesis,study on the problem of adaptive trajectory tracking control for underactuated surface ships has been carried out.The adaptive back-stepping method is used to estimate the model parameters and external environmental disturbances,and then an adaptive trajectory tracking controller based on the propeller thrust and rudder moment is designed.At the same time,an adaptive trajectory tracking controller based on rudder angle and propeller revolution is designed using SMC and ADRC technology.The research results obtained have a certain reference value for trajectory tracking control of underactuated surface ships.