Dual-loop robust controller design for autonomous underwater vehicle under unknown environmental disturbances

A dual-loop robust controller is proposed for precise position control of an autonomous underwater vehicle under uncertain hydrodynamics and unknown disturbances. In the inner-loop, a time-delay controller is presented in which a time-delay estimator estimates uncertain hydrodynamics and unknown disturbances from its time-delayed information and cancels these, thereby reducing control efforts on internal dynamics considerably. In the outer-loop, the linear controller stabilises the position error of the AUV without prior knowledge on values of hydrodynamic parameters. The proposed dual-loop controller features simple structure and easy implementation because it does not require real-time estimation of hydrodynamics.