Alternative rotor designs for high performance brushless permanent magnet machines for hybrid electric vehicles

This paper investigates different rotor topologies based on the spoke design as an alternative to the internal permanent magnet design currently used in the Toyota Prius 2004 design. Reference is made to the 2010 model where the magnet material and maximum torque are reduced, but the speed is doubled. A rare-earth spoke design is shown to be a viable alternative. The paper then goes further and investigates a ferrite alternative. While the torque density is reduced, it illustrates that the spoke magnet arrangement may a viable solution and may open up ferrite magnet use. To offset the reduction in torque density then the speed may be increased; this is the solution Toyota used in the 2010 machine for rare-earth magnet material reduction.