Fault detection and tolerant control with a variable-bandwidth extended state observer for electro-hydraulic servo systems with lumped disturbance and measurement noise.

In this study, a novel fault detection and tolerant control method are presented for electro-hydraulic servo systems (EHSS) with actuator partial loss of effectiveness (LOE) fault. Meanwhile, the parameter uncertainties, external disturbances, and output measurement noise are also considered. Firstly, we construct a new mapping function with a simple and flexible structure, and then design a variable-bandwidth extended state observer (VBESO) based on this function to estimate the states and lumped disturbance of the system. The designed VBESO can not only balance estimation accuracy and noise sensitivity, but also decouple the fault component from the lumped disturbance, thus facilitating fault detection. Subsequently, we design an adaptive law with time-varying gain that can accurately approximate the actuator LOE coefficient, and propose a stable fault detection scheme by combining the designed adaptive law, with the detection results that are less affected by changes in system states. The mutual coordination of the mentioned decoupling, adaptive law, and time-varying gain is a key feature of our method, rarely seen in other works. Furthermore, a fault-tolerant controller with the proposed VBESO and adaptive law is developed, which can guarantee that, even in the presence of the considered adverse obstacles, the hydraulic cylinder maintains high tracking accuracy and the control performance can be promptly recovered after an actuator fault occurs. Finally, the proposed method is validated by simulations and experiments, and it is compared with other controllers in different scenarios.