System identification of a three-phase submerged arc ferrosilicium furnace

A 36 MW submerged are ferrosilicium (FeSi) furnace is modelled using system identification. The main purpose is simulation and evaluation of different control schemes. In particular, the part of the system associated with the control of the electrode currents, which is done by positioning of the electrodes, is examined. The existing electrode current controller is effectively composed of three SISO loops, each controlling one electrode current independent of the others. However, there is a considerable coupling between the electrodes. Further, the noise environment is severe, which is partly due to large conductance changes in the charge. Data were collected at Icelandic Alloys Ltd., using experiments conducted mostly in open-loop. The positioning of electrodes responding to control signals was, however, estimated from measurements in closed-loop. Different ARX (autoregressive with auxiliary input) MIMO models were tried using various model orders, combinations of inputs and input delays. Then, dependent parameters due to symmetry in the three electrodes, as well as common factors (zeros) in the three input (electrode) polynomials were eliminated. The model selected was validated using various procedures