The design, implementation and experimental testing of a control system for an autonomous underwater vehicle (AUV) are described. The paper introduces the nonlinear dynamic model of a prototype AUV named MARIUS and formulates a general problem of vehicle control for precise manoeuvring in the vertical and horizontal planes. The methodology adopted for control system design is nonlinear gain-scheduled control, whereby a set of finite H-infinity controllers is scheduled on the vehicle speed. The paper summarises the basic design steps and decribes a new method for the practical implementation of nonlinear gain-scheduled control systems that avoids some of the pitfalls described in the literature. Experimental results obtained during the sea trials with the vehicle in Sines, Portugal, are presented and discussed.
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