Ocean Engineering 34 (2007) 842–849 Robust trajectory control of underwater vehicles using time delay control law R. Prasanth Kumar, A. Dasgupta à , C.S. Kumar Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur 721302, WB, India Received 8 November 2005; accepted 5 April 2006 Available online 18 September 2006 Abstract A new control scheme for robust trajectory control based on direct estimation of system dynamics is proposed for underwater vehicles. The proposed controller can work satisfactorily under heavy uncertainty that is commonly encountered in the case of underwater vehicle control. The dynamics of the plant are approximately canceled through the feedback of delayed accelerations and control inputs. Knowledge of the bounds on uncertain terms is not required. It is shown that only the rigid body inertia matrix is sufficient to design the controller. The control law is conceptually simple and computationally easy to implement. The effectiveness of the controller is demonstrated through simulations and implementation issues are discussed. r 2006 Elsevier Ltd. All rights reserved. Keywords: Underwater vehicle; Time delay control; Robust control; Adaptive control 1. Introduction Underwater vehicles have become an important tool for undersea intervention in recent years. Advances in certain key technologies like energy storage, navigation, etc., are making underwater missions more economical through autonomous underwater vehicles (AUVs). Precise position and attitude control are very important for underwater surveys using AUVs since the quality of data obtained is directly related to it. AUVs are required to operate autonomously in the absence of human intelligence. Underwater vehicle dynamics is highly nonlinear, coupled and time-varying. In addition to these, the hydrodynamic parameters are often poorly known and the vehicle may be subjected to unknown forces due to ocean currents. These difficulties make the control problem challenging. Good quality surveys can be made possible through efficient trajectory control of the vehicle. Several control techniques have been proposed in literature to deal with uncertainty. They can be broadly classified as robust approaches and adaptive approaches. Yoerger and Slotine (1985) proposed sliding mode controller for trajectory control of underwater vehicles neglecting the cross coupling terms. Healey and Lienard (1993) used multi- variable sliding mode control for diving, steering and speed control of underwater vehicles with decoupled design. Fossen and Sagatun (1991) used adaptive control with online estimation of uncertain parameters. Choi and Yuh (1996) made an experimental study on underwater robots using non-regressor-based adaptive control with bound estimation. Antonelli et al. (2003) proposed an adaptive control law which takes into account the hydrodynamic parameters affecting the tracking performance. Mrad and Majdalani (2003) showed that composite adaptive control law with bounded gain forgetting converges faster than tracking error-based adaptation. Li and Lee (2005) designed an adaptive nonlinear controller for depth control of underwater vehicles with fins without restriction on the pitch angle of diving. Compared to robust control, adaptive control is considered to be better for plants with uncertainties because it can improve its performance with adaptation with little or no information of the bounds on uncertainties ARTICLE IN PRESS www.elsevier.com/locate/oceaneng 0029-8018/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.oceaneng.2006.04.003 à Corresponding author. Tel.: +49 170 4837 883; fax: +91 3222 255303. E-mail addresses: rprasanthkumar@gmail.com (R. Prasanth Kumar), anir@mech.iitkgp.ernet.in (A. Dasgupta), kumar@mech.iitkgp.ernet.in (C.S. Kumar).