Abstract: An output feedback control algorithm with command filtering is proposed to solve the problem of uncertain nonlinear and unmeasurable state in the nonmatching model of electro-hydraulic servo systems. Through the effective integration of the extended state observer and command filtering technique, the state and external disturbances of the system are estimated by the extended state observer, the unmeasurable and uncertain nonlinear state problems are solved, and simultaneously the active compensation for disturbances is implemented. In process of controller design, the ‘differential explosion’ problem in backstepping scheme is avoided by using the command filter. Based on the Lyapunov function, the stability of the designed controller is proved and all the signals are bounded. The experimental results verify the effectiveness of the designed controller.

Key words: electro-hydraulic servo system; command filtering; output feedback control; extend state observer