Application of Soft Magnetic Composites (SMCs) in Position-Sensorless Controlled Radial Active Magnetic Bearings

In this paper a soft magnetic composite (SMC) material is applied to permanent magnet (PM) biased radial active magnetic bearings (AMB) and investigated regarding position-sensorless control. A bias flux generation by per- manent magnets with a homopolar bearing structure requires the closure of the bias flux in axial direction. Thus, accordant magnetic properties in all three dimensions are required from the applied materials. The isotropic behav- ior of SMCs may offer advantages compared to a classical realization with laminated electrical steel. Further, for a self-sensing AMB operation the high frequency (HF) aspects of the iron path have relevance for the sensorless position evaluation regarding dynamics and accuracy. Because of these two reasons applying SMC material to this AMB topology is an interesting alternative to common setups with laminated electrical steel. Two AMB proto- types at same geometry and different materials are investigated by experiments. In this work key parameters of bias flux density, force-current characteristic, operational losses and self-sensing properties are compared. Finally, a conclusion shows, that the apparent material advantages of SMC are not utilized in this AMB application.