Review and Enhancements of Rotor Designs for High Speed Synchronous Reluctance Machines

Rare earth metals are particularly required as a basic component of permanent magnets in modern traction drives for electric vehicles. Due to the limited global resources of raw materials, the environmental impact of mining and the challenges of recycling, the development of resource-saving alternatives is an important research topic. One option is the use of a synchronous reluctance machine (SynRM), whose rotor does not require magnetic materials, aluminum or copper due to its operating principle. Besides the cost-effective manufacturing, the robust and resource-saving rotor design and high efficiency of SynRM, this machine type suffers from a low power factor, poor torque and power density and earlier power drop in the field weakening range in comparison to permanent-magnet synchronous motors. These disadvantages result from the fragile design of the rotor lamination stack and the resulting limited maximum permissible operating speed of current industrial motors, which are therefore not yet suitable for traction drive applications. This paper gives an overview of new rotor concepts and designs which aim to increase the maximum operation speed of SynRM by optimizing the structural design. Subsequently, a new rotor topology is discussed and evaluated, especially regarding its mechanic and electromagnetic properties as well as the suitability for series production.