A regressor-free robust adaptive controller for autonomous underwater vehicles

This article focuses on the motion control of autonomous underwater vehicles in the ocean environment by a robust adaptive controller in which there is no regressor matrix. Due to the different atmospheric conditions in the ocean environment, the hydrodynamic coefficients of autonomous underwater vehicles cannot be exactly available and there are many uncertainties in the dynamic model. This prevents the traditional controllers to overcome these difficulties immediately. Hence, developing the adaptive controllers for the autonomous underwater vehicles encountered with uncertainties is required to provide appropriate performance. In the conventional adaptive control system, it is assumed that the autonomous underwater vehicle dynamic model can be linearly written into regressor form. Since the dynamics of the underwater vehicles is very complex, the derivation of the regressor matrix is very tedious. To overcome these problems, a regressor-free adaptive controller is proposed for the autonomous underwater vehicles in the general form of the equations of motion. In this approach, the controller is derived by the inverse dynamic method. Also, by utilizing known basis functions weighted by constant unknown coefficients, the uncertainties of the control law are estimated. The adaptation laws are derived based on Lyapunov stability theorem. The validity of the proposed method is verified by some simulation experiments. The simulation results show that the proposed approach can improve the robustness of adaptive controller to the dynamic model uncertainties and the external disturbance.