Double-Loop Structure Integral Sliding Mode Control for UUV Trajectory Tracking

To solve the problem of trajectory tracking control for the underactuated unmanned underwater vehicle (UUV) in external current disturbance, a back-stepping sliding mode control method with double-loop structure is proposed in this paper. The outer-loop controller constructs the position error sliding surface through desired position error, obtains the kinematics control law by combining with power reaching law, and gets the error of virtual velocity after completing the design of trajectory tracking kinematics controller. The inner-loop controller constructs the sliding surface of longitudinal, horizontal, and vertical velocity error, respectively, with the help of the UUV speed error. Also, the trajectory tracking dynamic controller is designed by combining with the exponential reaching law, where the control moment is almost chattering-free. The stability of the double-loop control system is proved by combining with the Lyapunov stability theory. Finally, the simulation experiments verify the high effectiveness of the algorithm.