Refined sliding mode disturbance observer-based finite-time composite control for Euler-Lagrange systems with multiple disturbances

A wide range of practical control systems such as robot manipulators and spacecrafts can be modeled by Euler-Lagrange systems. On one hand, the requirements for system control accuracy, response speed, and robustness are ever increasing. On the other hand, the control performances are inevitably degraded by multiple disturbances. In this paper, a novel finite-time composite control law is proposed for a class of Euler-Lagrange systems subject to multiple heterogeneous disturbances including a neutrally stable disturbance and a norm-bounded disturbance. More specifically, a refined sliding mode disturbance observer (RSMDO) is proposed to estimate and reject the neutrally stable disturbance in the feedforward channel, while an adaptive nonsingular backstepping control (ANBC) is designed in the feedback channel to stabilize the system and attenuate the observer error as well as the norm-bounded disturbance. The proposed RSMDO can not only fully utilize the disturbance information, but also quantify the convergence time and steady-state accuracy of the estimation error. The finite-time stability analysis is carried out for the closed-loop system. Finally, an example of spacecraft attitude control system is given to demonstrate the effectiveness of the proposed methods.