Comparison of single piece and fir tree based spoke type rotor designs for low cost electric vehicle application

Abstract

Permanent magnet motors with ferrite magnets may be applicable to demanding electric vehicle (EV) applications, provided that designs with high power density and efficiency, and high resistance to demagnetization are developed. One rotor topology that allows meeting those challenges is a spoke type design, which can consist of two sections that are connected via a so-called fir tree structure, or a single section that may accommodate flux barriers with a certain topology. In this paper, a magneto-structurally optimized single piece rotor design for a high speed-high power density EV application is disclosed and compared against an existing fir tree based rotor solution. It is shown that an optimally designed single piece rotor design can meet about 80% of the power density of a fir tree rotor design at the cost of ∼3 percent lower efficiency. Furthermore, the single piece rotor design may have better demagnetization resistance during severe faults. The theoretical findings have been supported by the static torque and demagnetization testing of a custom built prototype with the disclosed single piece rotor topology.