Sliding-mode observers for state and disturbance estimation in electro-hydraulic systems

In this paper, the comparison between a sliding mode observer and a high-order sliding mode observer for hydraulic actuators is presented considering different sets of available measurements, parametric uncertainties and model nonlinearities. The friction acting on the hydraulic cylinder and a dead-zone in the valve have been taken into account as uncertain disturbances acting on the system. For comparison purposes, the observation results are set side by side with the ones provided by an extended Kalman filter. Several simulations have been conducted in order to analyze the performance of the estimators, particularly with respect to the possibility of estimating the disturbances and unknown dynamics acting on the system, also in presence of measurement noise. Finally, experimental results are presented to validate the effectiveness of the proposed observers in real conditions.