Robust Control and Analysis of a Towed Underwater Vehicle

This paper presents an analysis of the dynamics and performance of a towed underwater vehicle and a study into the robust control design of such a vehicle. Firstly, the open-loop dynamical model is analysed to enhance understanding of its controllability and observability. The use of H-infinity is advocated to combat the uncertainties inherent in the complex non-linear model, the discrepancies arising between non-linear and linear models and any unknown disturbances. However, a novel procedure for automating the choice of weighting functions in the design process is introduced. This includes a performance, or quality, index dependent on user-specified parameters including time- or frequency-domain terms. The resulting controller performance is comprehensively analysed by means of both simple and complex channel commands applied to the non-linear simulation. An adaptive scheme involving a multivariable identification procedure is then proposed to improve the performance in a wide range of the trim point. A discussion of the consequences of this scheme is given.