Disturbance Observer-Based Double-Loop Sliding-Mode Control for Trajectory Tracking of Work-Class ROVs

The open-frame structure of work-class ROVs results in significant model uncertainties, and its motion is strongly disturbed by the umbilical cable. To address these problems, this article developed a nonlinear disturbance observer-based super-twisting double-loop sliding-mode control (NDO-STDSMC) method to achieve trajectory tracking control of work-class ROVs with system uncertainties and external disturbances. First, a new outer-loop controller with a novel reaching law is designed to increase the convergence rate compared with the existing double-loop sliding-mode control (DSMC). Second, an inner-loop controller that combines the advantages of the super-twisting sliding-mode scheme is proposed to guarantee the tracking error converges to zero in finite time. Then, a nonlinear disturbance observer is designed to estimate and compensate for the system uncertainties and external disturbances. The stability of the overall control system is proven by the Lyapunov approach. Finally, comprehensive simulation studies on trajectory tracking control of work-class ROVs are provided to demonstrate the efficiency of the proposed NDO-STDSMC method and its superiority over existing DSMC and STDSMC methods.