Non-singular terminal sliding mode control for robust trajectory tracking control of an autonomous underwater vehicle

The nonlinear trajectory tracking control design of an autonomous underwater vehicle (AUV) is a challenging task because of highly uncertain nature of ocean environment, time varying nonlinear vehicle dynamics and poorly known hydrodynamic coefficients of the vehicle. This paper addresses a trajectory tracking control problem for a class of nonlinear, highly coupled with motion in six degrees-of-freedom (DOF) AUV. The robust tracking control is achieved by designing an non-singular terminal sliding mode control (NTSMC) for complete nonlinear model of an AUV. The proposed control scheme assures finite time convergence of the systems states due to addition of a nonlinear term into linear sliding surface results in nonlinear sliding mode called terminal sliding mode (TSM). In addition, the problem of singularity associated with conventional terminal sliding mode control (TSMC) is overcome by the proposed control scheme. Numerical simulations on an experimental AUV is performed for complex reference trajectory to test the efficacy of the controller. Also the proposed NTSMC is capable of handling the hydrodynamic parameter uncertainties, unidentified disturbances like ocean current and measurement sensor noises.