Comparative study between interior and surface permanent magnet traction machine designs

Interior permanent magnet (IPM) brushless (sychronous) machines are a popular technology choice in commercial hybrid- or all-electric vehicles (HEVs/EVs), such as the Toyota Prius, GM Chevy Volt, Lexus LS, Nissan Leaf, for example. Much is claimed of IPM topologies in terms of their saliency torque contribution, minimum magnet mass, demagnetisation withstand, wide flux-weakening capability and high operational efficiencies when compared to brushless machines having surface mounted permanent magnets. This paper presents the findings of a comparative study assessing the design and performance attributes of an example IPM machine implemented in the Nissan Leaf EV, when compared to a surface permanent magnet (SPM) machine designed within the main Nissan Leaf machine dimensional constraints. The Nissan Leaf IPM traction machine has been widely analysed and there is much public domain data available for the machine. Hence, this machine is chosen as a representative benchmark design against which the SPM machine is assessed. The Nissan Leaf machine is analysed via finite element analysis (FEA) and the results confirmed via published experimental test data. The procedure is then applied to a SPM design and results compared. The study illustrates and concludes that both the IPM and SPM topologies have very similar capabilities with only subtle differences between the design options. The results highlight interesting manufacturing options and materials usage.