Robust Path‐Following Control of Underactuated AUVs with Multiple Uncertainties in the Vertical Plane

Abstract

The current study employs a novel nonlinear robust control approach for path‐following control of underactuated autonomous underwater vehicles (AUVs) with multiple uncertainties in the vertical plane. Firstly, a nonlinear underactuated AUV model is established to characterize the dynamics of AUV and path‐following error. To resolve dependence on a detailed model that ap-peared in previous studies, the unknown time‐varying attack angular velocity in the dynamic model of the path‐following error is considered as the kinematic uncertainty, while the linear superposition of the external environmental disturbances, the perturbations in the internal model parameters, and other unmodeled dynamics in the dynamic model is chosen as lumped dynamic uncertainties. Several reduced‐order extended state observers (ESOs) are designed for estimating both of these uncer-tainties. Secondly, to reduce the impact of input saturation and avoid the “explosion of complexity” associated with traditional back‐stepping method, a nonlinear track differentiator (NTD) is utilized to follow the virtual control signal and its derivative. Thirdly, the constructed reduced‐order ESOs and NTD are adopted to establish an augmented back‐stepping controller, where its ability to sta-bilize the overall system is demonstrated using the Lyapunov theorem. Finally, extensive simulations and analyses in various working conditions, including the nominal working condition without disturbances, the working condition with multiple uncertainties, and the conditions which better replicate the actual environment, are performed to demonstrate the effectiveness, superiority, and robustness of the designed controller.