Designing the Controller of a Servo Valve by Simulation

The paper presents the research activities aiming to design the controller of a high flow electro-hydraulic servo valve needed for the power stage of the speed governors controlling high power hydraulic turbines operating under low oil pressure. This is the common case of any Kaplan turbine, but the refurbishing of the old Francis turbines needs the same valve configuration. Design problems, simulation methods and experimental researches are briefly presented. From an industrial point of view, the main idea of the new concept is the use of high-quality industrial electro-hydraulic and electronic components only, in order to obtain good performances even under a low-pressure supply. This target generated a new approach of the design by eliminating the pipes between the flow control stages. A detailed model of a high power servomechanism containing a three-stage non-linear electro hydraulic proportional servo valve was designed by simulation, taking into account the real geometry of the metering spool windows. The valve dynamic behaviour was simulated with SIMULINK and AMESIM, and finally the results were compared with some preliminary laboratory measurements. The simulated and the real responses for different inputs were found in good agreement.