Sliding Mode Control for Digital Hydraulic Applications

The digitalisation of hydraulic drives leads to a simpler hardware, but asks for novel and sometimes even complex control strategies. This paper deals with the application of sliding mode control to a digital hydraulic drive. The sliding mode control is an approach for nonlinear systems with a discontinuous actuating variable, which makes it a favourable controller particularly for hydraulic switching control. An additional advantage is the robustness compared to the variation of system parameters. A linear hydraulic drive with a specific digital circuit for which an experimental setup, called "Digi Actuator" exists, is used as example for this case study. The mathematical system model is transformed to Byrnes-Isidori normal form, for which a derivation of the sliding mode controller can be performed in a systematic way. The simulation results confirm the known advantages of this control concept, robustness even for quite nonlinear systems.