Design, analysis and control of a semi-active magnetic bearing system for rotating machine applications

In this paper, a semi-active magnetic bearing system which incorporates both the active and passive magnetic bearings is proposed for rotating machine applications. Particularly, the design, analysis, and control issues of the semi-active system are investigated by using an axial fan as the platform. In the proposed system, while the rotor is levitated axially by the active bearing, its radial and tilting stabilities are guaranteed by the passive bearings. By carefully designing the radial and tilting stiffnesses of the passive bearings and the controller of the active bearing, the system can be successfully operated to the rated speed of 4000rpm. Because the semi-active magnetic system is frictionless and consumes insignificant power in levitation, its total power consumption is 14.7% less than the conventional fan in which mechanical ball bearings are used.