A high torque, wide air gap bearingless motor with permanent magnet free rotor

This paper introduces a bearingless motor topology with a magnet free rotor, which enables higher rotor torque densities and wider air gap compared to previously published topologies. Flux density in the air gap and therefore torque capability is maximized by a stator in temple configuration, which provides large winding space. The low number of eight stator and six rotor teeth keeps stray flux low, which enables wider air gap ratios at the same time. A challenge of having a low teeth number are large angle dependent force and torque nonlinearities, which are compensated in the control algorithm. A 3D FEM optimized prototype was constructed and put into operation. Measurements of the running system are presented to confirm the feasibility of the introduced topology.