Extended disturbance observer-based sliding mode fault-tolerant control for the dual-valve hydraulic servo system with reduced-order model

This paper presents an analysis of an extended disturbance observer-based fault tolerant control method for a dual-valve hydraulic servo system applied in mobile machinery. The dualvalve hydraulic servo system comprises a parallel configuration of a proportional valve and a servo valve, which act as system actuators to drive a hydraulic cylinder. In this article, the external disturbance and actuator faults are integrated together into a new lumped uncertainty term by reducing the system order in the way of introducing singular perturbation theory. Thus, an extended state disturbance observer is designed to estimate the lumped disturbance term. To tackle those serious actuator failures in view of the parallel valves and guarantee system tracking performance, a switching function index is proposed. Additionally, a sliding mode control scheme is deployed to enhance the performance of the control law by suppressing the estimated disturbance and the effects of the actuator faults. The global stability of the suggested control algorithm is proved through the Lyapunov theory. Finally, co-simulations are carried out to illustrate the effectiveness of the proposed method. The results show that the proposed fault-tolerant controller together with the extended disturbance observer, provides excellent tracking performance in the presence of external disturbance, and valve faults such as jam or failure.