High Power Density Design of 6-Slot-8-Pole Hybrid Excitation Flux Switching Machine for Hybrid Electric Vehicles

Over the last decade, many automotive companies have been commercializing hybrid electric vehicles (HEVs) as one of candidates for sustainable human life. Some of the recent HEVs employ electric propulsion systems using a combination of reduction gear and interior permanent magnet synchronous motors (IPMSM) operated by relatively high-speed more than 12 000 r/min, resulting in achieving high torque and power densities simultaneously. In the combination, since all rare-earth permanent magnets are embedded in its rotor core, a machine design of high-speed IPMSM tends to be difficult. This is due to a design confliction between keeping enough mechanical strength of the rotor core and bringing out better electromagnetic performances. To cope with this problem, this paper deals with a 6-slot-8-pole hybrid excitation flux switching machine, in which both permanent magnets and wound field excitation are employed as magnetomotive force sources. This machine has all active parts on the stator body and a rugged rotor structure similar to that of switched reluctance motor suitable for high-speed operation. Some design parameter refinements are conducted to the machine in order to elevate maximum torque capability and maximum power density as much as possible under given design requirements and constraints. As a result, it is demonstrated that the machine designed becomes a good candidate for the target HEV drive application.