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.