Feedback linearization-based position control of an electrohydraulic servo system with supply pressure uncertainty

Electrohydraulic servo systems (EHSS) are used for several engineering applications, and in particular, for efficient handling of heavy loads. proportional-integral-differential (PID) control is used extensively to control EHSS, but the closed-loop performance is limited using this approach, due to the nonlinear dynamics that characterize these systems. Recent studies have shown that feedback linearization is a viable control design technique that addresses the nonlinear dynamics of EHSS; however, it is important to establish the robustness of this method, given that hydraulic system parameters can vary significantly during operation. In this study, we focus on supply pressure variations in a rotational electrohydraulic drive. The supply pressure appears in a square-root term in the system model, and thus, standard adaptive techniques that require uncertain parameters to appear linearly in the system equations, cannot be used. A Lyapunov approach is used to derive an enhanced feedback-linearization-based control law that accounts for supply pressure changes. Simulation results indicate that standard feedback-linearization based control is robust to EHSS parameter variations, providing significant improvement over PID control, and that the performance can be further improved using the proposed control law.