Dynamic circuit model of a radial magnetic bearing with permanent magnet bias and laminated cores

Abstract

A hybrid radial magnetic bearing (HRMB) with permanent magnet creating bias flux is used to reduce the power consumption. Laminated cores are widely used in HRMB to reduce eddy currents. Nevertheless, when the frequencies of rotation and control currents are extremely high, eddy-current effects in laminated iron cores still have a significant influence on the behavior and performance of magnetic bearings. In order to predict performance and guide design of the HRMB system in high frequency, an analytical method based on equivalent circuit model whose parameters are frequency-dependent is used in this paper. The analytical results show that, the eddy currents induced due to rotor movement and dynamically changing control currents will result in considerable magnitude decrease and phase lag of bearing stiffness. Furthermore, the eddy current effect on HRMB can be reduced by increasing the air gap, decreasing the laminations thickness and decreasing the laminations conductivity. Finally, a prototype is designed and fabricated; the experimental results demonstrate the validity of the analysis.