Dual-Purpose No-Voltage Winding Design for the Bearingless AC Homopolar and Consequent Pole Motors

A winding design approach is proposed for the bearingless ac homopolar and consequent pole motors that utilizes the same coils for both suspension force and torque production. This enables a “pure” bearingless motor design, where the same iron and copper are used for both magnetic bearing operation and torque production, and can result in more optimal machine performance. Separate terminal connections are provided for suspension and torque operation; the suspension terminals experience no motional-emf when the rotor is centered, thereby reducing the required voltage rating of the bearingless drive compared to other “dual purpose” winding designs. It is shown that only certain combinations of stator slots, phases, and poles yield suitable winding designs; most notably, the number of motor pole-pairs must be co-prime with the number of phases. A design procedure is proposed which allows the designer to simply modify end-connections of many conventional armature windings, including both integral- and fractional-slot windings; an example winding design is presented and analyzed using 3-D finite element analysis (FEA); and a hardware prototype has been constructed with experimental results included to validate the proposed design approach.