Adaptive Backstepping Sliding Mode for Underactuated AUV Trajectory Tracking Based on Ocean Current Observer

The hydrodynamic parameters are uncertain when the underactuated autonomous underwater vehicle (AUV)sails with a certain depth in the ocean, and the underactuated AUV is also disturbed by external disturbances such as ocean currents. It poses a major challenge to trajectory tracking accuracy. This paper studies the trajectory tracking control problem of underactuated AUV in the horizontal plane under the ocean current environment. The current velocity is applied to the kinematics and dynamics equation by specifying the transformation relationship between an inertial reference frame and a body-fixed reference frame, and then the kinematic model and dynamic model of underactuated AUV with current can be calculated. The trajectory tracking error equation can be obtained in conjunction with the desired trajectory. The adaptive backstepping sliding mode controller(AB-SMC)for AUV horizontal trajectory tracking is designed by adding an adaptive rate. Moreover, an ocean current observer is devised to measure the ocean current velocity to reduce the navigation trajectory deviation of the actual AUV trajectory. The simulation results show that AB-SMC realizes the estimation of total uncertainties consisting of hydrodynamic parameters uncertainties and external time-varying disturbances and make up for the shortage of the precise model parameter and disturbance information in traditional backstepping sliding mode controy theory. And the ocean current observer can improve the tracking accuracy of the underactuated AUV. Theoretically, the whole AUV cascade control system consisting of AB-SMC and the ocean current observer is globally asymptotically stable. The simulation comparison diagrams show that the proposed AB-SMC based on ocean current observer can resolve the effects of hydrodynamic parameter uncertainty, ocean current disturbances, and other unknown disturbances. Furthermore, its tracking efficiency is better than the ocean current observer-based backstepping trajectory tracking controller(BTTC). © 2020, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.