Fuzzy Optimal Fault-Tolerant Trajectory Tracking Control of Underactuated AUVs With Prescribed Performance in 3-D Space

This article proposes a fuzzy optimal fault-tolerant control scheme with prescribed performance for three-dimensional trajectory tracking control of underactuated autonomous underwater vehicles (AUVs) in complex ocean environments, especially in the presence of unknown actuator faults and dynamic uncertainties. The scheme has the following features. 1) The underactuation problem is overcome by defining new system outputs. 2) An error transformation method that removes restrictions on initial error conditions is adopted to achieve global prescribed performance control. 3) A fuzzy adaptive disturbance observer based on a generalized fuzzy hyperbolic model (GFHM) is proposed to estimate compound disturbances consisting of actuator faults, dynamic uncertainty parts and disturbances. 4) Based on adaptive dynamic programming techniques, a single critic structure fuzzy optimal controller is developed using a GFHM to obtain an approximate optimal control law. In particular, actuator faults, dynamic uncertainties, and disturbances are uniformly handled by structuring an improved cost function and solving optimal control of the nominal system. Through analysis, the proposed scheme can ensure that all signals of the AUV closed-loop system are uniformly ultimately bounded and the original tracking errors can remain within prescribed boundaries. Pure software and hardware-in-the-loop simulations demonstrate the effectiveness and advantages of the proposed scheme.