| Unmanned surface vehicle(USV)is an intelligent surface robot with autonomous navigation ability.When USV is equipped with different work modules,it can carry out different marine tasks.Therefore,scholars and engineers pay much attention to the researches and development of USV.The accurate trajectory tracking of USV is the primary premise for completing various marine tasks,so trajectory tracking control has become one of the hot issues in USV research.Due to the physical properties of thruster,the design of trajectory tracking controller for USV is often affected by actuator dead-zone,saturation and time-delay limits.If the limitation of actuator is ignored,it will not only lead to the fact that the USV cannot accurately track the reference trajectory,but also cause damage to the actuator,and even cause serious consequences such as shipwreck.Therefore,the limitations of the above actuator must be considered in the practical engineering application of USV.In this paper,the optimal control theory is used to design the optimal trajectory tracking controller for the trajectory tracking control system of the USV with actuator limitation.The dynamic tracking performance of the USV is improved and the high-precision tracking of the reference trajectory is realized.The specific research contents are as follows:Firstly,a trajectory tracking optimal control policy based on backstepping and adaptive dynamic programming is proposed to solve the trajectory tracking optimal control problem of USV with dead-zone limitation.The control policy can accurately track the reference trajectory and ensure the optimal dynamic tracking performance.The problem of actuator dead-zone limitation is also solved.Secondly,aiming at the optimal trajectory tracking problem of USV with actuator saturation,a prescribed-performance optimal trajectory tracking control policy is proposed with reinforcement-learning based Actor-Critic framework.The control strategy effectively overcomes the influence of discontinuous differentiability of saturation function,at the same time,the dynamic tracking error of USV is constrained within a specified range,which improves the performance of the dynamic and ensures the optimality of trajectory tracking controller.Then,an optimal control policy based on optimized backstepping method is proposed to solve the optimal problem of USV trajectory tracking with actuator time-delay.The control strategy combines the backstepping and Actor-Critic framework to ensure that the virtual and the actual controller of the USV trajectory tracking control system are optimal controllers,and effectively overcome the influence of actuator time-delay.By designing a neural network approximator,the influence of unknown dynamics and inaccurate modeling are eliminate.Finally,the stability of the above USV trajectory tracking control systems is verified according to Lyapunov stability criterion.The simulation experiment also verifies the effectiveness and superiority of the proposed optimal trajectory tracking controller with the above three limitations. |
