A Double Closed-loop Integral Sliding Mode Controller for Position and Attitude Tracking of Underwater Vehicle

A double closed-loop integral sliding mode control method (DISMC) is studied and applied to the position and attitude tracking control of underwater vehicle. Firstly, the position and attitude tracking model and the environment interference model are established to adapt to the structure characteristics of the underwater vehicle. Secondly, to solve the steady-state error caused by external disturbance in the process of position and attitude tracking and improve the robustness of the control system, a double closed-loop integral sliding mode control algorithm is designed based on Lyapunov stability theory. The integral sliding mode surface is designed to eliminate the steady-state error of the system. The virtual control law derived from the outer loop control realizes the position and attitude tracking control; the virtual control law is transmitted to the inner loop as the control input so that the inner loop sliding mode control law can track the velocity and angular velocity to eliminate the disturbance. The simulation results show that such control algorithm can realize the precise position and attitude tracking control of the underwater vehicle. Moreover, compared with the traditional PID control algorithm, the new algorithm presents better control effect and stronger robustness responding to the combined action of constant current and external time-varying disturbance.