First order mechanical sizing equations for the electromagnetic optimization of spoke IPM machines

The dovetailed spoke interior permanent magnet (IPM) electric machine rotor has gained popularity over the past few years. The first machine prototype of this type was a design with NdFeB magnets. This rotor topology limits the magnet leakage flux associated with IPM designs that use the lamination structure to mechanically support the magnets and rotor structure by eliminating the need for magnetic bridges and posts. The price and sustainability of rare earth elements has driven a concern of the long term availability of rare earth magnets like NdFeB that use both neodymium (Nd) as well as the heavy rare-earth dysprosium (Dy) used to stabilize the demagnetization of these magnets at higher temperature. There has been a focused global effort to reduce or eliminate the need for rare-earth materials. This paper will cover the first order mechanical sizing equations that have been developed and used in the power density optimization of a non-rare earth magnet ferrite spoke design.