Saturated exponential super-twisting sliding mode control for bottom-following of biomimetic underwater vehicles with unmeasured velocities

This article addresses the bottom-following problem for biomimetic underwater vehicles without translational velocity measurements in the presence of complex uncertainties and actuator saturation. A novel saturated exponential super-twisting algorithm based integral terminal sliding mode control (SESTA-ITSMC) scheme is created to ensure fast convergence and strong robustness as well as attenuate the chattering of actuators. Salient features are as follows. Instead of discontinuous term in the conventional super-twisting algorithm, a novel SESTA is developed by incorporating a fractional power term, which ensures that the system achieves a faster transient response, effectively eliminating the chattering phenomenon. Then, to deal with the unknown states and further improve the anti-interference ability of the system, the finite-time dual estimator is devised to fast and precisely estimate the translational velocities and lumped uncertainties. Finally, a finite-time anti-windup auxiliary system is proposed to compensate for the saturation constraints on actuators in real time. Finite-time convergence of estimation errors and bottom following errors is guaranteed by the Lyapunov stability theory. Comparative simulation results fully demonstrate the excellence of the proposed SESTA-ITSMC scheme.