By Thomas Jahns Getting rare-earth magnets Out of eV Traction machines A review of the many approaches being pursued to minimize or eliminate rare-earth magnets from future EV drivetrains. HERE ARE NOW MORE THAN 1.5 million plug-in hybrid electric vehi- cles (HEVs) and battery electric vehicles (BEVs) that have been commercially pro- duced in the world during the past 11 years, and it is likely that the number produced during 2016 exceeded 700,000, a new record. A large percentage of those electrified vehi- cles use ac permanent magnet (PM) synchronous machines for the traction machines used in their drivetrains. Even more specifically, nearly all of these PM synchronous machines fall into the class of inte- rior PM (IPM) synchronous machines. The origin of this name becomes apparent by inspecting the cross section of a typical IPM machine in Figure 1 that has been simplified to highlight the key features. This figure shows that the magnets are buried in cavities inside the rotor, and the cavities are carefully shaped, often in V configura- tions, to concentrate more of the PM magnetic flux into the machine's air gap. So what accounts for the popularity of the IPM synchronous machine in EVs? The major fea- tures that make it appealing include those in the following list. T Digital Object Identifier 10.1109/MELE.2016.2644280 Date of publication: 7 March 2017 6 I E E E E l e c t r i f i cati o n M agaz ine / march 2017 IMAGE LICENSED BY INGRAM PUBLISHING 2325-5987/17©2017IEEE