Analysis and Reduction of Magnet Loss by Deepening Magnets in Interior Permanent-Magnet Machines With a Pole/Slot Ratio of 2/3

Interior permanent-magnet (IPM) machines are desirable for electrical vehicles due to high power density and good flux-weakening capability. This paper focuses on the approaches to reduction of magnet eddy-current loss in IPM machines with a pole/slot ratio of 2/3, taking a 16-pole/24-slot machine as an example. By comparing permanent-magnet losses between a surface-mounted magnet machine and an IPM machine, the spatial filter effect on even-order stator magnetomotive force space harmonics is highlighted. Thereafter, the effect of magnet depth on magnet eddy-current loss is investigated. Moreover, the constraints on reduction effect of magnet's depth, such as copper loss and torque ripple, are analyzed. A 16-pole/24-slot IPM machine prototype is manufactured after the tradeoff design. The experimental results validate the effect of magnet depth on reducing magnet losses.