Evaluation of efficiency optimized variable flux reluctance machine for EVs/HEVs by comparing with interior PM machine

As one of crucial components for electric vehicles (EVs) and hybrid electric vehicles (HEVs), the electrical machine has been widely evaluated from the prospective of machine topology, torque density, permanent magnet usage, and efficiency. In this paper, novel variable flux reluctance machines (VFRMs), which do not have either brush/slip-ring or rare-earth permanent magnet, is evaluated for EV/HEV application with emphasis on driving efficiency. Two VFRMs are designed to compare with the interior permanent magnet machine (IPMM) used in Toyota /Prius 2010. Both machines have the same outer diameter as that of IPMM. However, one is with the same core length as the IPMM; the other one is with the same machine axial length as IPMM accounting for the end-windings. Based on the quantity evaluations of average torque, torque/power-speed characteristic, efficiency map and energy consumption during the city and highway drive cycles, the VFRM shows it can be a prospective low cost candidate for the EV/HEV application by providing the comparative torque density, efficiency and small torque ripple similar to the IPMM.