Performance Measurement and Mathematical Model Identification of the Hydraulic Servo Control System of a Vacuum Electric-Arc Furnace

The static and dynamic performances of the hydraulic servo control system of the electrode in a VHD vacuum electric-arc furnace have been measured. There is a large dry friction area in the performance of cylinder, which is provided by the vacuum seal on the electrode. Through theoretical analysis, the block diagram of the system is obtained. The dry friction can be represented by a negative feedback of cylinder velocity and is proportional to the unit velocity vector of cylinder. For the identification of the mathematical model of the system, a pulse signal is applied into the electrical panel and the responses of the spool displacement of the servo valve and cylinder velocity are recorded under open-loop condition. By discretization of the response curves r the Laplace transforms of valve displacement and cylinder velocity can be calculated. Then the transfer function of the servo valve and the cylinder can be derived by curve fitting. In the procedure of derivation, the dry friction is treated as the unit velocity vector feedback.