Passification of an electrohydraulic two-stage pressure control servo-valve

Passive systems have the beneficial property that their interconnections with other passive systems result in necessarily stable systems. This virtue of passive systems can be exploited with hydraulic systems to build powerful machines that are safe and human friendly. A difficulty in applying the passivity concept to electrohydraulic systems is that they are not intrinsically passive. In a previous paper, passification techniques were developed to render single-stage directional control valves as passive two-port devices with a supply rate related to the power input at the hydraulic port. In this paper, we extend the passification technique to two stage pressure control servo-valves. The passified two-stage valve avoids the flow rate and bandwidth limitations that exist for single-stage valves.