Design and axial position control of a small-sized active magnetic bearing with non-laminated core

Abstract

Active magnetic bearings (AMBs) are an electromagnetic device which supports rotor without mechanical contact and lubrication by using the attractive electromagnetic force controlled by electronic control system. Main advantages of magnetic bearings are divided into two groups: first, there is no mechanical contact between rotating part and fixed part, which enables no mechanical friction and wear, no lubrication requirements, low energy consumption, leading to longer life time and very high circumferential speed compared with that of conventional oil film bearings. Second, it is possible to electrically control the system. This enables the rotor position control, the adjustment of stiffness and damping, and the continuous monitoring of operating condition. Also, it is possible to control the force and stiffness of the handling point, measure the external load, and control the vibration of rotor. The various advantages of the AMB have lead to wide application in industrial fields. In the past thirty years, AMBs have bee used as non-contact support in many industrial field, and the industrial machinery gets small and precise by development of electric, material, and manufacturing parts. When AMB is applied to the miniaturized rotating machinery, the drawback of AMB is rotational power loss. In order to fully utilize the many advantages AMB, the ability to accurately predict losses becomes a necessity. This work focuses on the development of the small-sized AMB with solid cores and rotor to be able to operate at high speed. As the size of rotor with AMBs gets smaller, lamination of cores and rotor becomes increasingly difficult to effectively reduce the eddy current effect. Thus the accurate modeling of eddy current loss becomes important for the small-sized AMB systems with solid cores and rotor. Also, new structure is applied to the axial magnetic bearing to miniaturize the AMB. In this work, the eddy current loss equation is proposed based on the model of eddy...