Flatness-Based Nonlinear Control for Position Tracking of Electrohydraulic Systems

In this paper, a flatness-based nonlinear controller is proposed to improve the position-tracking performance and to reduce the current input ripple in electrohydraulic systems (EHSs). The proposed method consists of feedforward control using a flatness concept and feedback control to yield a stable control system. This paper presents an analysis on the problem of tracking a reference position, conditions for open-loop stability, as well as an analysis on the flatness of EHS. These results are used for a nonlinear feedforward control design. To further improve the position-tracking performance, feedforward control is augmented with a nonlinear feedback control, which is designed based on the flatness property of EHSs. Moreover, the state variable derivatives are not used so that the measurement noise and structural vibration are not amplified, which in turn can increase the machinery's life expectancy because the current inputs' ripples are reduced.