An enhanced backstepping approach for motion control of underactuated autonomous surface vessels with input constraints

This paper focuses on the motion control of an underactuated autonomous surface vessel (UASV). A robust adaptive approach is proposed to control the UASV in spite of existence of uncertainties in the dynamic model and the external disturbances by integrating the backstepping method with input constraints, functional approximate technique (FAT) and projection operator. In the proposed controller, it is not required to compute the complex functions and their derivatives appearing in the traditional backstepping methods. The motion control strategy of the UASV is first derived based on the backstepping method. Then, the complex functions, appearing in the controller, are estimated by the FAT and Lyapunov based adaptive laws. This causes the inherent complexity of the backstepping technique, numerical derivatives of virtual inputs, is to be overcome. Moreover, the input limitations are considered by an auxiliary system. Stability analysis of system is performed by Lyapunov’s direct method. Several numerical simulations are carried out to confirm the effectiveness of the proposed method.