Non-linear Adaptive Control System for an Underactuated Autonomous Underwater Vehicle using Dynamic State Feedback

An adaptive, non-linear control strategy for underactuated Autonomous Underwater Vehicle (AUV) is proposed in this paper. In order to improve the autonomy of AUVs, it is important to develop intelligent control systems which can reduce the effects of coupled and non-linear characteristics of the vehicles. As most of the AUVs are under actuated systems, classical control scheme fails due to the non-integrable acceleration constraints on the vehicle. A dynamic state feedback law is proposed here to overcome this and to reduce the modelling errors arising out of various assumptions on the vehicle dynamics. In addition, proposed method can work satisfactorily under commonly encountered uncertainties such as ocean current and parameter variations. The system states are stabilized by forcing the tracking errors to an arbitrarily small neighborhood of zero by using backstepping technique and the tracking error dynamics. The proposed strategy has been tested through simulations, for a flat-fish type AUV. A comparison of the results for conventional method and the proposed method is also presented.