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 example. By comparing PM losses between a surface mounted magnet (SPM) machine and an IPM machine, the spatial filter effect on even order stator magnetomotive force (MMF) space harmonics is highlighted. Thereafter, the effect of magnet depth on magnet eddy current loss is investigated. Moreover, the constraints on reduction effect of magnets depth, such as copper loss and torque ripple, are analyzed. A 16-pole/24-slot IPM machine prototype is manufactured after tradeoff design. The experimental results validate the effect of magnet depth on reducing magnet losses.Index Terms-IPM machines, magnet loss reduction, magnet depth, tradeoff design. 0018-9464 (c)