Prescribed Performance Output Feedback Nonlinear Robust Control for Electro-Hydraulic Servo Systems Based on Extended State Observer

This paper presents a nonlinear control strategy with output feedback and predefined performance to address modeling uncertainties, nonlinearities, and composite disturbances in electro-hydraulic servo systems. A predefined performance function is established to constrain control error, and the transformed error based on this framework is employed for controller design. A backstepping method is then used to synthesize an Extended State Observer (ESO) along with a nonlinear robust controller. The proposed controller accommodates not only composite disturbances and nonlinear characteristics-such as the nonlinear flow behaviors of servo valves-but also modeling uncertainties, including parameter estimation errors and unmodeled dynamics. Furthermore, the controller is theoretically guaranteed to achieve specified tracking performance and ultimate tracking accuracy, with Lyapunov analysis employed to confirm its stability. Finally, simulation results are compared, with Matlab/Simulink simulations conducted to validate the effectiveness of the proposed approach.