Robust variable-depth path following of an under-actuated autonomous underwater vehicle with uncertainties

This paper treats the subject of variable-depth path following control of an under-actuated autonomous underwater vehicle (AUV) with multiple uncertainties. The modeling uncertainties of the investigated AUV are composed of inaccurate hydrodynamic coefficients and unknown environmental disturbances. For this uncertain system, a nonlinear control law integrating line-of-sight (LOS) guidance with fuzzy sliding mode control (FSMC) algorithm is designed to guarantee global K-exponentially convergence of path following errors. The LOS guidance in the Serret-Frenet frame is adopted to guide the under-actuated AUV to move towards the curved variable-depth path. The sliding mode control algorithm ensures the stability and the robustness of the designed control law in the presence of multiple uncertainties. The fuzzy logic algorithm is integrated to adjust sliding mode gain in order to weaken chattering. In addition, the angle of attack is considered in the design of dynamics control law to ensure that the under-actuated AUV follows the predefined path with a given resultant speed. Finally, a comparative simulation study illustrates the effectiveness of the designed FSMC algorithm for variable-depth path following of an under-actuated AUV with multiple uncertainties.