Objective To address the high-performance trajectory tracking control problem for the unmanned underwater vehicle (UUV) under external disturbances, this paper proposes a non-singular integral terminal sliding mode control (NITSMC) scheme based on a nonlinear disturbance observer (NDOB).

Methods First, the dynamic equation of UUV with lumped disturbances is established, and an NDOB is designed to estimate the lumped disturbances. On this basis, an NITSMC law is designed to effectively compensate for the disturbances, achieving fast and precise tracking of the desired trajectory. Finally, the effectiveness and superiority of the designed NDOB-NITSMC control scheme are validated through comparative simulations against the integral sliding mode control (ISMC) and PID control methods. Additionally, the effectiveness and practicality of NDOB-NITSMC are confirmed on the BlueROV2 UUV platform through water tank experiments.

Results The results show that, in high-fidelity simulations, the NDOB-NITSMC scheme ensures that the position and orientation errors of BlueROV2 converge to a small neighborhood around zero within 8 seconds, with root mean squared errors (RMSEs) of 0.31, 0.22, 0.29 centimeters, and 0.23 degrees, respectively. The convergence speed and control accuracy surpass those of ISMC and PID control methods. In water tank experiments, the NDOB-NITSMC scheme ensures that the position and orientation errors of the UUV converge to a small neighborhood around zero within 15 seconds, with RMSEs of 2.31, 2.56, 2.17 centimeters, and 1.11 degrees, respectively. Additionally, the control inputs are smooth, ensuring its suitability for practical engineering applications.

Conclusion The proposed NDOB-NITSMC scheme effectively addresses the high-performance trajectory tracking control problem for UUVs under external disturbances and demonstrates promising prospects for engineering applications.