Test results for a high temperature non-permanent magnet traction motor

Commercially available hybrid and electric vehicles are generally using rare earth PM motors because of their compactness and very good efficiency. But the supply security and price volatility of rare-earth materials are still major concerns for the hybrid and electric vehicle industry. Hence, global efforts are underway in several countries on using reduced or non-rare earth materials, developing non-permanent magnet solutions and taking cost out by trading off between material properties and cost. Non-permanent magnet machines are generally known to be less power dense than permanent magnet counterparts. But the absence of permanent magnets in these machines makes them well suited for high temperature applications provided appropriate stator winding insulation materials are used. This offers a degree of freedom in improving their power density because they can operate at higher electrical loading while maintaining acceptable efficiency. This paper presents a high temperature DC biased reluctance machine which is structurally similar to a conventional switched reluctance machine. This non-permanent magnet machine has a DC field winding and an AC three phase armature winding. The machine is equipped with a high temperature 280°C rated insulation system. Test results showing machine performance under continuous operation against the FreedomCar 2020 specifications as well as at high temperature up to 280°C are presented. A 43% improvement in power density was achieved by going to high temperature.