IEEE Electrification Magazine - March 2017 - 19

By Margarita P. Thompson,
Edwin Chang, Aldo Foto,
Jorge G. Citron-Rivera,
Daad Haddad, Richard Waldo,
and Frederick E. Pinkerton

Grain-boundaryDiffused magnets
The challenges in obtaining reliable and representative
BH curves for electromagnetic motor design.

YBRID ELECTRIC VEHICLES (HEVs) AND ELECTRIC VEHICLES (EVs)
frequently have interior permanent magnet-type motors where
the permanent magnets are embedded inside the rotor in one or
more layers with V-shaped poles. In general, the permanent magnets in an EV motor are subjected to high levels of a demagnetizing field (large motor current with high control angle). To protect the magnets
from being permanently demagnetized due to this high demagnetizing field, it is
essential that they exhibit high coercivity. Thus, the permanent magnets most
commonly used in these cases are neodymium iron boron (main phase:
Nd2Fe14B), as these provide a superior combination of high remanence (Br) and
high coercivity (Hcj) under typical motor operating conditions. However, to
ensure high magnetic properties at high temperatures, these magnets traditionally need to be heavily alloyed with heavy rare-earth (HRE) elements such as
dysprosium (Dy) or terbium (Tb). Depending on the application, as much as 10%
of Dy and Tb by weight can be required to ensure high magnetic properties at
the desired temperature. It is desirable to reduce and even eliminate the use of
HRE elements in NdFeB magnets to decrease cost and avoid price fluctuations or
supply uncertainties, which are of major concern to the automotive industry.

H

Digital Object Identifier 10.1109/MELE.2016.2644561
Date of publication: 7 March 2017

2325-5987/17©2017IEEE

IEEE Electrific ation Magazine / march 2 0 1 7

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