Performance limitations of a class of two-stage electro-hydraulic flow valves

By examining the dynamics of a popular type of two-stage electronic proportional valve, this paper addresses its performance limitations, with both cautions in control implementation and suggestions in valve design. While several benefits do exist, there are limitations to the closed loop performance of the valve when it is included in a valve-controlled electro-hydraulic system. These limitations come from the structural feature that the pilot flow not only controls but also contributes to the total flow. Although for steady state performance this design gives a higher flow efficiency, for dynamic performance it results in zeros in the open loop transfer function, which will limit the closed loop bandwidth of a flow control system. A non-linear analytical model of this particular type of valve is derived first. It is then simplified as a reduced order linear model with the inherit system zeros illustrated. Validation of the analysis is obtained by experimental results on a testbed.