Global robust tracking with disturbance attenuation for unmanned underwater vehicles

We present a solution to the global reference tracking problem with disturbance attenuation for a general model of an underwater vehicle. For such a system the use of robust control schemes is mandatory, due to the significant model uncertainty and the strong influence of external disturbances such as the underwater current. The approach described consists of designing a nonlinear control law based on backstepping techniques, which solves the problem of robust asymptotic tracking with uniform disturbance attenuation for a nominal model of the vehicle dynamics, and then employing robust redesign based on high-gain feedback to counteract the effects of the model perturbation. As a result, we are able to uniformly bound the mean-square tracking error by an arbitrary positive constant. We obtain a global result, since a nonsingular parametrization of the vehicle attitude has been assumed. Simulation results show the application of the proposed methodology to the control of a remotely operated vehicle.