Dynamic Output Feedback Fault Tolerant Control for Unmanned Underwater Vehicles

In this paper, we propose a dynamic output feedback fault tolerant control (FTC) scheme to achieve trajectory tracking for an unmanned underwater vehicle (UUV) subject to actuator faults, actuator saturation, external disturbances and other system uncertainties. To make matters more challenging, it is assumed that the velocities (linear and angular) are unavailable. In this condition, the UUV motion model in the horizontal plane has a high relative degree, thus increasing the design complexity. In contrast to observer-based FTC schemes, we introduce a dynamic compensator, which produces an augmented error system whose dynamics is minimum phase and relative degree one. An adaptive learning observer is then introduced to address the composite uncertainties arising from actuator faults, uncertain nonlinearities, actuator saturation and disturbances. We show that the proposed scheme can ensure that the trajectory tracking errors converge to a small neighbourhood around zero. Finally, a simulation example is used to prove the efficacy of the proposed scheme.