Improved Nonsingular Fast Terminal Sliding Mode Control of Unmanned Underwater Hovering Vehicle

An improved nonsingular fast terminal sliding mode manifold based on scaled state error is proposed in this paper. It can significantly accelerate the convergence rate of the state error which is initially far from the origin and achieve the fixed-time convergence. In addition, conventional double power term based reaching law is improved to ensure the convergence of sliding state in the presence of disturbances. The proposed approach is applied to the hovering control of an unmanned underwater vehicle. The controller exhibits both fast convergence and strong robustness to model uncertainty and external disturbances. © 2022, Shanghai Jiao Tong University.