In-situ parameter identification and optimal unbalance control of active magnetic bearing system

Abstract

Active magnetic bearing(AMB) is an electromagnetic device to suspend a rotor without any mechanical contact and lubrication by using attractive electromagnetic forces controlled by electronic control system. Mechanical non-contact provides the possibility of high circumferential speed and no friction and wear in the magnetic bearing. In particular, no lubrication considerably reduces routine maintenance, eliminates sealing requirements, and make it possible to operate in severe environment such as vacuum, steam, cryogenics, sterile and corrosive atmosphere. It can be compensated for tool wear, control shaft position, and adjust stiffness and damping during operation of the machinery by electronic control. AMBs have been increasingly utilized for many industrial applications because of their excellent advantages over conventional mechanical bearings. The AMB requires more accurate design and prediction of dynamic behavior to improve its performance, reliability and stability as a component of overall rotor bearing system with industrial application growth. However AMB systems often show discrepancies between the predicted and the measured dynamic behaviors due to the inaccurate and complicated modeling associated with the frequency characteristics of power amplifiers and electromagnets, and magnet flux loss and delay such as eddy current, leakage and fringing effects. Therefore accurate system parameter identification becomes a crucial factor when it is necessary to improve the system performance and stability making some prediction on the system. The identification of AMB system is mainly concerned with the dynamic characteristic analysis of the controlled system, the use of magnetic bearings as exciters, and the development of algorithm for parameter identification. But most studies on system identification in the past are confined to parameter identification fore controller design without considering dynamic characteristics of the rotating machinery or simpl...