Adaptive Yaw Control for an Unmanned Surface Vessel System with Transient Error Analysis

In this paper, an adaptive tracking control technique is proposed to stabilize the yaw angle of an unmanned surface vessel (USV) system subject to input saturation and external disturbances. Unlike existing saturation systems and disturbance rejection methods, the proposed control scheme simultaneously considers input saturation and unknown disturbances in a unified adaptive framework. First, an adaptive second-order system is presented to compensate for control input saturation. Such a saturated system can effectively reduce the amplitude of controller output. Then, an adaptive learning law is designed to estimate online the unknown upper bound of an external disturbance, removing the requirement for prior information on the disturbance. Based on Lyapunov stability theory, the convergence of the tracking error of closed-loop system and the uniform boundedness of all closed-loop signals are strictly proved. Furthermore, the transient performance of the real yaw tracking error is analyzed by considering the selected Lyapunov function, and an explicit upper bound of the transient error is derived for the first time in USV yaw control. Finally, simulations are carried out to illustrate the effectiveness of the proposed controller.