Dynamic Factor Models of a Thrust Magnetic Bearing With Permanent Magnet Bias and Subsidiary Air Gap

A hybrid thrust magnetic bearing (HTMB) with permanent magnet creating bias flux is used to save energy. The eddy currents have a fundamental impact on the dynamic characteristics of the magnetic bearing system. Therefore, the dynamic factor models affected by the eddy currents rather than static model are required to insure reliable and effective operation. The dynamic factor models affected by the eddy currents for the HTMB with permanent magnets and subsidiary air gap are presented in this paper. The equivalent magnetic circuit models of the HTMB are given and derived to calculate the dynamic force-current factor and the dynamic force-displacement factor. Furthermore, the dynamic factors of the HTMB are also investigated by the transient nonlinear finite element method (FEM). The analytical results show that the two dynamic factors have the different frequency response characteristics, both in the equivalent magnetic circuit model and from the results of the nonlinear FEM. Furthermore, the distribution of flux density in the air gap at different frequency response is shown and compared to static flux by using FEM. The dynamic performance is determined by the dynamic force-current factor model due to the difference between the control flux path and the permanent magnet bias flux path. The analysis results calculated by the simplified analytical model agree well with the results calculated by transient FEM.