Control of hydraulic drives using more than two pressure lines is studied as a means for improving energy efficiency, e.g. for excavators or for hydraulic power take off from sea wave power plant systems. All combinations of switching n different pressure levels to a differential cylinder provide in general 2.n force levels. In order to facilitate forces between these levels for a proper motion control, this digital concept was combined with throttling control. This, of course, causes energetic losses. In this paper a combination of multi-pressure and switched inertance control is presented and studied theoretically by mathematical modelling and simulation. The integration of the switched inertance part requires only a pipeline as an inertance element and a so called “Mikota resonator” flow and pressure ripple suppression. Simulation results show a good motion control performance and an efficiency gain over intermediate force adjustment by throttling in load lifting.
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