Robust Tracking Control for Underactuated Autonomous Underwater Vehicles

The underwater environment is highly dynamic in nature due to unknown dynamic model parameters and unknown external disturbances. Under such an uncertain environment, a control problem of underactuated underwater vehicles poses significant challenges. This paper presents the robust design of a dynamic adaptive sliding mode control (ASMC) followed by a kinematic controller for a 4DOF underactuated vehicle to track the reference velocity and desired trajectory, respectively. Lyapunov candidate function is used to prove the convergence of the error variables close to the origin. The effectiveness of the designed control method is investigated by comparing it with traditional sliding mode control (SMC) and PID control through simulation runs. Time-varying disturbances are considered to validate the robustness of the designed control law. The other system parameters are taken from an existing prototype of an autonomous underwater vehicle. The simulation results validated the effectiveness and superiority of the proposed ASMC as compared to the contrast controller.