Two-degree-of-freedom robust control for a non-minimum phase electro-hydraulic system

Electro-hydraulic actuator (EHA) system inherently suffers from uncertainties, nonlinearities and time-varying in its model parameters which makes the modeling and controller designs are more complicated. The main objective of this paper is to perform a robust control design using discrete-time sliding mode control (DSMC) with two-degree-of-freedom control strategy. The proposed controller consists of feedback and feedforward combination which capable to reduce phase lag during the trajectory tracking of EHA system. The feedforward controller is developed by implementing the zero phase error tracking control (ZPETC) technique which the main difficulty arises from the nonminimum phase system with no stable inverse. Finally, a chaotic trajectory tracking is performed in the experimental works to show the robustness of DSMC controller and performance comparison is made with Linear-Quadratic-Regulator (LQR) and Proportional-Integral-Derivative (PID) controllers. The findings show that the proposed controller with ZPETC outperforms the LQR and PID controllers in terms of tracking accuracy.