Performance Limits of Permanent-Magnet-Biased Magnetic Bearings

Abstract

An active magnetic bearing with electromagnets only is unavoidably bulky and power-consuming. These shortcomings can be remedied by using permanent magnets as the source of bias flux. Unlike the hybrid magnetic bearings with the same flux path for both permanent magnets and electromagnets, so-called coplanar PEMBs, a non-coplanar PEMB with permanent magnets located between two sets of electromagnets, which are placed around the periphery of the shaft, cannot be regarded as equivalent to a pure electromagnet magnetic bearing. This paper analyzes the performance limits, such as maximum static bearing force, force slew rate, displacement sensitivity, and dynamic load capacity, of the non-coplanar PEMBs. We also campare the characteristics of this type of magnetic bearing to the co-plane PEMBs and point out their differences. Investigation of these performance limits enable better utilization of permanent-magnet-biased magnetic bearings and offer useful guidelines for the design of this type of magnetic bearing.