L1 Adaptive depth and pitch control of an underwater vehicle with real-time experiments

This paper proposes a new control scheme for underwater vehicles. These systems are highly nonlinear and they often operate in a varying environment. A robust controller is therefore needed to deal with these challenges. The recently developed L1 adaptive controller is proposed to be designed and implemented in real time for the first time on an underwater vehicle. Different experimental scenarios are then conducted to test the performance of the closed-loop system in two degrees of freedom. An interesting particularity of this controller lies in its architecture where robustness and adaptation are decoupled enabling thus high adaptation gains. This would result in a fast adaptation with a guaranteed smooth transient response without any persistency of excitation. In order to validate the choice of this controller, a comparative study is proposed to be conducted with the well proven adaptive nonlinear state feedback controller (ANSF). Real-time experimental results are proposed for different scenarios including nominal case, external disturbances rejection and robustness towards parameters uncertainties. This comparative study highlights clearly the superiority of the L1 adaptive controller.