Fixed-time sliding mode output feedback tracking control for autonomous underwater vehicle with prescribed performance constraint

This paper studies the trajectory tracking control problem for autonomous underwater vehicles (AUVs) subject to external disturbances and model uncertainties. To improve the tracking performance of the AUVs, a prescribed performance function is introduced to constrain the output tracking error. Then, a fixed-time extended state observer (FxTESO) is set up to estimate the unknown states and the lumped disturbances (including external disturbances and model uncertainties). With the outputs of the FxTESO, a novel dynamic fixed-time terminal sliding mode (FxTTSM) surface is constructed and then a fixed-time output feedback controller is designed to achieve trajectory tracking control for the AUVs. By employing Lyapunov function theory, the stability of the closed-loop system is analyzed. Simulation results are provided to verify the effectiveness of the developed control scheme.