A new approach for three-dimensional trajectory tracking control of under-actuated AUVs with model uncertainties

Abstract

This paper presents a study of precisely three-dimensional (3-D) trajectory tracking controller design for AUV vehicles regarding to highly uncertain nonlinear model features, internal/external disturbances, and roll motion's effect. Firstly, the six degrees of freedom (6-DOF) nonlinear equations of motion are described. Subsequently, a novel control scheme is proposed based on cascade structure, which divides the control problem into dual-coupled problems, called kinematic control and dynamic control. Furthermore, four nonlinear disturbance observers (NDOs) are innovatively constructed to handle the errors in the linearization process and the uncertainties in the 6-DOF AUV model as well. In the kinematic control, Lyapunov's direct method is adopted to compute the desired values for surge velocity, pitch angle, and heading angle to force the trajectory tracking error to an arbitrarily small neighborhood of zero. In the dynamic control, back-stepping sliding mode control is applied in designing attitude and velocity controllers. Finally, strict inspection added with benchmark tests are specific evidence showing the feasibility, effectiveness, disturbances rejection ability, and robustness of the proposed control scheme.