Fault-tolerant synchronization control for a dual redundant electro-hydraulic actuator system based on velocity estimation

Considering the fact that the piston velocity measurements of electro-hydraulic actuators are not available in practice, a fault-tolerant synchronization control strategy based on piston velocity estimation is proposed to deal with the positon tracking problem for a Dual Redundant Electro-Hydraulic Actuator System (DREHAS) suffering from Internal Leakage Common-Mode Fault (IL-CMF) and disturbances. First, by introducing two groups of reference trajectory and a linear transformation of the system states, the decoupling of the control surface position tracking and the two actuators output force synchronization control is realized. Second, an Adaptive Extended State Observer (AESO) is designed to estimate the piston rod velocities and disturbances of the two-channel actuators, which overcomes the inaccuracy of the estimation results of Extended State Observer (ESO) under fault condition. Finally, based on the state estimation and the online adaptation of faulty parameters, a nonlinear fault-tolerant synchronization controller is developed by employing backstepping method. Lyapunov stability analysis indicates that the proposed scheme can ensure that all the signals of the closed-loop system are bounded and the system can achieve a prescribed tracking performance under IL-CMF and time-varying disturbances. Moreover, the system tracking error converges to zero asymptotically in the present of IL-CMF and constant disturbances. A simulation experiment validates that the proposed control scheme is effective.