Active Fault Tolerant Control for Unmanned Underwater Vehicle With Actuator Fault and Guaranteed Transient Performance

In this paper, an active fault tolerant control (FTC) scheme is proposed to achieve trajectory tracking of unmanned underwater vehicle (UUV) subject to multiple uncertainties (external disturbances and modeling errors), actuator saturation and actuator fault. More challengingly, it is assumed that the linear and angular velocities are unavailable. The proposed scheme includes a fault detection (FD) unit, a fault isolation (FI) unit and an FTC unit. The FD is performed by an adaptive interval observer (IO), where adaptive parameters instead of uncertainty bounds are used. The adaptive parameters change automatically until the interval widths between outputs and their upper/lower bounds reach a given range which is independent of uncertainty bounds. Hence the proposed FD scheme not only provides tighter upper and lower bound estimates of states, but also is more sensitive to faults. The FI unit which consists of a set of IOs determines the location of actuator fault. The FTC unit is developed to guarantee that the tracking errors satisfy the desired transient performance, where the unmeasurable states are expressed as a linear combination of their upper and lower bounds, provided by the FD and FI observers, and no additional state observers are needed to estimate unmeasurable states. Finally, simulations are conducted to verify the effectiveness of the proposed scheme.