Performance-guaranteed fractional-order sliding mode control for underactuated autonomous underwater vehicle trajectory tracking with a disturbance observer

This paper proposes a fractional-order sliding mode control method for an underactuated autonomous underwater vehicle (AUV) with random disturbances. First, a new fractional-order sliding mode disturbance observer (FOSMDO) is designed to estimate the random disturbance and unknown AUV's model based on adaptive and fixed time. A strategy based on adaptive fractional sliding mode control is designed for motion control, and a line-of-sight guidance law with time-varying look-ahead distance is applied to achieve path following. Then, a new fractional-order sliding model controller is designed by constructing a fractional-order mode surface and proposing a prescribed performance function to ensure the control performance. The closed-loop stability is proved and analyzed, and the effectiveness and robustness of the controller are demonstrated by numeric simulations.