Disturbance observer based finite-time exact bottom-following control for a BUV with input saturation

This paper proposes an improved finite-time disturbance observer (IFTDO)-based finite-time control (IFTDO-FTC) scheme for implementing exact bottom-following of a biomimetic underwater vehicle (BUV) subject to input saturation and complex uncertainties. First, an improved dynamic model is proposed to deal with the problem of periodic input signals due to fish-like locomotion, in which the generalized forces are divided into average forces and periodic forces, where the periodic forces are regarded as extra external disturbances. Second, to estimate the lumped uncertainties, an improved finite-time disturbance observer is firstly designed by introducing a new second order finite-time differentiator, which can estimate disturbances fast and accurately as well as inhibit chattering induced by sign functions. Third, integral terminal sliding mode control frameworks are adopted to stabilize the bottom-following errors in finite time by incorporating the IFTDO and a finite-time bottom-following guidance law, in which finite-time auxiliary systems are employed to compensate for input saturation. Finally, simulations and comparisons are performed to demonstrate the superiority and robustness of the proposed IFTDO-FTC approach. © 2022 Elsevier Ltd