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This article proposes a novel bearingless motor topology with diamagnetic salient-pole rotor. The material of the rotor is pyrolytic graphite (PG) so that five degrees of freedom of the rotor are passively stabilized above a permanent magnet array. The stator consists of two components: a Halbach permanent magnet array and an axial-flux stator core with twelve teeth holding the eight-pole three-phase winding. Passive levitation forces are generated between the permanent magnet unit and the PG rotor. Rotating torque is generated between the stator core and the PG rotor. In this paper, the principle of the five-axis passively stabilized bearingless motor with the PG rotor is outlined. In experiments, passive axial forces and an acceleration process are measured. In the test, open-loop speed control is used. The proof-of-concept successfully achieves stable passive levitation, and allows acceleration up to 200 r/min.

This paper presents a design of high slot fill aluminum winding in permanent magnet machines for reducing winding losses. Generally, there is a trade-off between the winding weight and the winding losses. The winding DC loss is reduced with an increase of cross-sectional areas of conductors. In general, the aluminum winding is effective for reducing the winding weight, on the other hand, the winding loss is high because the electrical conductivity is low. In this paper, a high slot fill aluminum winding of 83.8% is proposed. It overcomes the trade-off, as a result, the winding losses are significantly reduced. In particular, reducing winding DC loss contributes the decrease of the whole winding loss including winding AC losses. Two prototype machines with the proposed aluminum winding and comparable round copper winding are fabricated and tested. In experiments, both winding DC loss and whole winding losses are measured in the proposed aluminum winding and the round copper winding machines. Consequently, it is demonstrated that the proposed aluminum winding machine can reduce the whole winding losses in wide frequency region. Furthermore, efficiency improvements can be also demonstrated in the proposed aluminum winding.