Global fixed-time trajectory tracking control of underactuated USV based on fixed-time extended state observer.

This paper studies the trajectory tracking problem of unmanned surface vehicle subject to unmeasurable velocities and unknown disturbances. By combining a fixed-time extended state observer (FESO) and a fixed-time differentiator, a fixed-time sliding mode control (FTSMC) law is proposed, in which a saturation function is adopted to make the terminal sliding mode surface leave the singularity area. The value of this paper can be described: first, this paper designs a novel guidance law that can converge in a fixed time to reduce the convergence time of the error. Then, unmeasurable velocities and lumped disturbances are estimated by applying a FESO. Meanwhile, a fixed-time differentiator is used to obtain real-time differential signals, thus reducing the difficulty of controller design. Subsequently, a novel auxiliary dynamic system is designed to address actuator saturation. According to Lyapunov's theory, the entire closed-loop control system has uniformly global fixed-time stability (UGFTS). The superiority of the designed controller is demonstrated through numerical simulations. • A novel fixed time guidance law is developed, which makes position errors reach zero within a fixed time. • A FESO is designed to estimate unknown dynamics within a fixed time, which does not require precise model parameters. • A novel auxiliary dynamic system is designed to handle input saturation, which can ensure that the state converges in finite time. • The fixed-time differentiator is introduced to achieve satisfactory filter and differential performance. • A novel FTSMC strategy is proposed for underactuated USV. Finally, the system proved to be uniformly global finite-time stable. [ABSTRACT FROM AUTHOR]