High-Speed IPM Machines With Structural Inserts

The increased popularity of electric propulsion systems for automotive vehicles has greatly intensified the interest in improving the performance of electric motors. Interior permanent magnetic motors, which place the permanent magnets between layers of electrical steel within the rotor, are of particular interest due to their high-power density and efficiency. However, the design of these rotors typically relies on a series of webs to link the electrical steel layers together and retain the magnets against the centrifugal forces generated by the rotation of the rotor. These webs result in flux leakage, which wastes some of the magnetic flux from the magnets, increasing the cost and reducing the power density. Here, we discuss an approach to eliminating some of this lost magnetic flux using structural non-magnetic metallic inserts to replace the center posts. Attention is given to the selection of material for the insert, the geometry of the insert, how to effectively tie together multiple layers of magnets, and manufacturability. A new method for mechanical testing or rotor coupons is developed and is used for experimental validation of the proposed concept.