Longitudinal motion control of underwater vehicle based on fast smooth second order sliding mode

Abstract By considering the influence of model uncertainty and external disturbance as well as combining theory of high order sliding mode with the recurrent hermite neural network (RHNN), this paper proposed a nonlinear robust control method for solving the longitudinal motion control problem of underwater vehicles. Based on the characteristics of multiple time scales, the longitudinal motion model was divided into inner and outer loops. The designed fast and smooth second order controller, which applied the discontinuous sign function on the derivative of the control law, was used in the outer loop. Then integration was performed to obtain the continuous sliding mode control law, which was applied to remove chattering and improve convergence rate. Furthermore, based on the controller of outer loop, the composite disturbance of the inner loop was effectively estimated using the combination between the fast smooth second order sliding mode controller and the RHNN disturbance observer. Therefore, the controller was effectively compensated, and the entire system’s stability in finite time was proved. The simulation results confirmed the promising performance and robustness of the proposed control method.