Observer based fixed-time integral sliding mode tracking control for underactuated AUVs via an event-triggered mechanism

Abstract

In this paper, a fixed-time control scheme is presented for trajectory tracking of underactuated autonomous underwater vehicles (AUVs) subject to external disturbances. An adaptive fixed-time disturbance observer (AFDO) is developed to estimate the external disturbances in fixed time without the prior knowledge of external disturbances. An event-triggered mechanism is introduced to save the bandwidth resources and reduce the communication burden. By synthesizing the developed AFDO and the event-triggered mechanism, an AFDO based event-triggered fixed-time integral sliding mode control (AFDO-EFISMC) scheme is proposed to force the AUV to track the reference trajectory in fixed time. With the aid of the developed AFDO, the gain of discontinuous control part of the designed control scheme is reduced, and therefore the control chattering is alleviated. Stability analysis is given to show that the designed AFDO-EFISMC scheme can make the tracking errors of the AUV converge to arbitrarily small neighborhood of the origin within a fixed-time independent of the initial conditions. The effectiveness of the proposed control scheme is proven by comparative numerical simulations.