Adaptive robust tracking control for underwater gliders with uncertainty and time-varying input delay

Abstract

Underwater gliders (UGs) profile vertically by changing buoyancy and generally do not employ sophisticated controllers for depth control, but instead the simple logic rules-based controller. This paper first raises the problem of UGs operating beyond the prescribed depth due to employing the conventional logic rules-based depth control (LRDC). In order to achieve effective depth and attitude tracking control, a dual closed-loop control structure based on integral sliding mode control (ISMC) and adaptive robust time-delay control (ARTDC) is proposed to deal with model uncertainties, environmental disturbances and time-varying uncertain input delays without any explicit knowledge of delay variation. A simplified reduced-order motion equation of UG in the vertical plane is described for the first time. Second-order extended state observers are designed to estimate the unmeasurable velocity and acceleration term of UG. The rigorous stability analysis based on Lyapunov synthesis conforms the uniform ultimate boundedness of the closed-loop system tracking error. Razumikhin-type stability analysis combined with linear matrix inequality technique is employed to facilitate the selection of controller parameters. Finally, simulation results compared with LRDC and proportional–integral–derivative with delay compensator scheme validate the good tracking performance and superior robustness of the proposed control scheme. Experimental studies show the practical effectiveness for preventing operating beyond the prescribed depth and tolerating the input delay.