| Autonomous Underwater Vehicle (AUV) control is a very challenging task because of AUV system nonlinearity, time-variance, uncertain external disturbance and difficulty in hydrodynamic modeling. Based on a detailed AUV control survey and description of AUV dynamics, this work proposes a novel controller that combines Disturbance Observer (DOB) and a regressor-free adaptive controller. DOB is used to cancel the effect of the external disturbance and modeling error, and the nonlinear regressor-free adaptive controller is used to handle the nonlinearity and disturbance estimation error, and to achieve desired control performance. The main characteristics of this controller are its robustness to the external disturbances and robustness to the nominal model parameter change. The latter one maps the big orientation change of the AUV during its underwater movement and the difficulty in AUV modeling.; Comparison experimentation is carried out to show the performance of this proposed adaptive DOB controller. Three other controllers are used for comparison purpose: PID controller, PID DOB controller and non-regressor adaptive controller. 4-DOF tests are done with the disturbance from heave, roll, pitch and yaw, and 6-DOF tests are done with the disturbance from surge and sway. The experimental results show that, comparing with the adaptive DOB controller, PID controller and adaptive controller are not robust to external disturbance, and PID DOB controller is not robust to the nominal model change. Therefore, comparing with these three controllers, the proposed adaptive DOB controller performs the best in terms of the external disturbance and the difficulty in AUV modeling. These make adaptive DOB controller ideal for AUV control. |
