This paper mainly contributes an anti-windup control scheme for path-following of underactuated autonomous underwater vehicles (AUVs) exposed to constrained inputs. First, a disturbance observer (DO) is employed to estimate the model uncertainties and external disturbances on the vehicle which is called mismatched lumped disturbance. Then, taking advantages of the time scale separation caused by different rates of numerous variables, a three-time scale singular perturbation control scheme is proposed for path-following of underactuated AUVs, leading to a control law with relatively simple structure and thus a reduction of the complexity in implementations. Furthermore, a novel disturbance observer-based anti-windup modification is developed to handle the possible input saturation, by means of time scale decomposition and so-called "manifold reconfiguration" in a geometric view. The stability for the overall system is also established. Finally, the results of simulation and experiment are illustrated to substantiate the efficacy of proposed method for path-following of autonomous underwater vehicles subject to disturbances and input constraints in the horizontal plane.
Note to Practitioners-Path-following is a fundamental motion control problem for AUVs. Despite a number of nonlinear control techniques having offered new tools and promising solutions to deal with the path-following problem of AUVs subject to model uncertainties and actuator saturation, they typically nonetheless yield relatively complicated controllerswhich may be prohibitive in the real world. Motivated by that, this paper aims to develop an alternative anti-windup control scheme, which should be capable of achieving satisfactory control performance, as well as be easy-to-implement in practical cases. To this end, it suggests a new approach using the theory of singular perturbation and time scales. In this paper, we first make good use of the difference between the bandwidths for observer and vehicle dynamics to design and analyze the DO, so