Model-based output feedback control of slender-body underactuated AUVs: Theory and experiments

This paper presents the design and experimental results of a novel output feedback controller for slender-body underwater vehicles. The controller is derived using model-based design techniques. Two separate control plant models are employed: a 3-degree-of-freedom (DOF) current-induced vessel model accounting for the current loads acting on the vehicle and a 5-DOF model describing the vehicle dynamics. The main design objective behind this strategy is to incorporate the vehicle dynamics when estimating the current influence on the vehicle. Furthermore, the transit model is based on the notion of constant propeller revolution resulting in a partly linearized model, which subsequently leads to perspicuous and implementable controller and observer structures. The controller is derived using the observer backstepping technique, and the closed loop is proved to be asymptotically stable using Lyapunov and cascaded systems theory. The control objective is to track the desired pitch and heading angle generated by the line-of-sight guidance system while keeping constant forward thrust. Experimental results demonstrate successful performance of the proposed output feedback controller implemented on the Minesniper MkII AUV/ROV.