IEEE Electrification Magazine - March 2017 - 7

xx
Like all types of PM synchronous machines, the

magnets, once magnetized, continually deliver mag-
netic flux into the machine's air gap without ex-
ternal excitation. This fulfills one of the key
prerequisites for torque production in any type of
electric machine by providing a magnetic field that
couples with the stator coils. The fact that this field
is created without the need for field excitation cur-
rent delivered by an external electrical power source
(e.g., batteries) saves energy as well as reduces heat
production inside the machine that would other-
wise be produced by resistive power dissipation in
the stator windings. This gives PM machines a
potent built-in advantage that can be used by
machine designers to achieve an adjustable combi-
nation of the key desired performance attributes for
EV traction machines: higher efficiency, smaller
mass and volume, and lower rotor inertia.
xx
By burying the magnets inside the rotor, as shown in
Figure 1, the IPM machine provides mechanical pro-
tection for the magnets, which is more important
than it might first appear because magnet materials
are typically brittle with tensile strengths that are far
lower than that of the lamination steel that sur-
rounds them.
xx
Less obvious from Figure 1 is the fact that IPM
machines provide highly valuable performance
advantages in the hands of a skilled machine designer
that make it much easier to shape the machine's
torque versus speed characteristics to match the
requirements of modern EV traction drives. In addi-
tion, IPM machines provide valuable opportunities
for reducing the amount of required magnet mate-
rial, which will be discussed in more detail later in
this article.
One of the key factors that gives rise to the last of
these advantages is that there is nearly an endless
number of IPM machine designs. These IPM machine

(a)

(b)

A-
C+

B+
C-

N

A+

B-
S

S

A+

B-

N

C-
B+

C+
A-

Figure 1. A basic IPM machine cross section.

designs are distinguished by key attributes that include
the orientation of the embedded magnets, the number
of layers of magnet cavities in each rotor pole, and the
placement of the magnets inside the cavities, which are
not necessarily filled completely with magnet material.
Some examples of IPM machine rotor cross sections
used in production EVs during the ten-year period from
2003 to 2013 are provided in Figure 2. In addition to
these variations in the IPM machine rotor design, the
choice of the stator winding configuration has a
dramatic impact on the machine's performance charac-
teristics as well.

The Problem with magnets
In general, the magnitude of the advantages enjoyed by
IPM machines increases monotonically with the strength

(c)

Figure 2. Examples of IPM machine rotors with sintered neo magnets used in production EVs: (a) the 2002 Toyota Prius (courtesy of ORNL
report by Hsu et al.), (b) the 2007 Toyota Camry (left) and 2008 Lexus LS 600h (right) (courtesy of ORNL report by Burress et al.), and (c) the
2013 Chevrolet Spark (photo courtesy of General Motors Company).

IEEE Electrific ation Magazine / march 2 0 1 7

7



Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2017

IEEE Electrification Magazine - March 2017 - Cover1
IEEE Electrification Magazine - March 2017 - Cover2
IEEE Electrification Magazine - March 2017 - 1
IEEE Electrification Magazine - March 2017 - 2
IEEE Electrification Magazine - March 2017 - 3
IEEE Electrification Magazine - March 2017 - 4
IEEE Electrification Magazine - March 2017 - 5
IEEE Electrification Magazine - March 2017 - 6
IEEE Electrification Magazine - March 2017 - 7
IEEE Electrification Magazine - March 2017 - 8
IEEE Electrification Magazine - March 2017 - 9
IEEE Electrification Magazine - March 2017 - 10
IEEE Electrification Magazine - March 2017 - 11
IEEE Electrification Magazine - March 2017 - 12
IEEE Electrification Magazine - March 2017 - 13
IEEE Electrification Magazine - March 2017 - 14
IEEE Electrification Magazine - March 2017 - 15
IEEE Electrification Magazine - March 2017 - 16
IEEE Electrification Magazine - March 2017 - 17
IEEE Electrification Magazine - March 2017 - 18
IEEE Electrification Magazine - March 2017 - 19
IEEE Electrification Magazine - March 2017 - 20
IEEE Electrification Magazine - March 2017 - 21
IEEE Electrification Magazine - March 2017 - 22
IEEE Electrification Magazine - March 2017 - 23
IEEE Electrification Magazine - March 2017 - 24
IEEE Electrification Magazine - March 2017 - 25
IEEE Electrification Magazine - March 2017 - 26
IEEE Electrification Magazine - March 2017 - 27
IEEE Electrification Magazine - March 2017 - 28
IEEE Electrification Magazine - March 2017 - 29
IEEE Electrification Magazine - March 2017 - 30
IEEE Electrification Magazine - March 2017 - 31
IEEE Electrification Magazine - March 2017 - 32
IEEE Electrification Magazine - March 2017 - 33
IEEE Electrification Magazine - March 2017 - 34
IEEE Electrification Magazine - March 2017 - 35
IEEE Electrification Magazine - March 2017 - 36
IEEE Electrification Magazine - March 2017 - 37
IEEE Electrification Magazine - March 2017 - 38
IEEE Electrification Magazine - March 2017 - 39
IEEE Electrification Magazine - March 2017 - 40
IEEE Electrification Magazine - March 2017 - 41
IEEE Electrification Magazine - March 2017 - 42
IEEE Electrification Magazine - March 2017 - 43
IEEE Electrification Magazine - March 2017 - 44
IEEE Electrification Magazine - March 2017 - 45
IEEE Electrification Magazine - March 2017 - 46
IEEE Electrification Magazine - March 2017 - 47
IEEE Electrification Magazine - March 2017 - 48
IEEE Electrification Magazine - March 2017 - 49
IEEE Electrification Magazine - March 2017 - 50
IEEE Electrification Magazine - March 2017 - 51
IEEE Electrification Magazine - March 2017 - 52
IEEE Electrification Magazine - March 2017 - 53
IEEE Electrification Magazine - March 2017 - 54
IEEE Electrification Magazine - March 2017 - 55
IEEE Electrification Magazine - March 2017 - 56
IEEE Electrification Magazine - March 2017 - 57
IEEE Electrification Magazine - March 2017 - 58
IEEE Electrification Magazine - March 2017 - 59
IEEE Electrification Magazine - March 2017 - 60
IEEE Electrification Magazine - March 2017 - 61
IEEE Electrification Magazine - March 2017 - 62
IEEE Electrification Magazine - March 2017 - 63
IEEE Electrification Magazine - March 2017 - 64
IEEE Electrification Magazine - March 2017 - 65
IEEE Electrification Magazine - March 2017 - 66
IEEE Electrification Magazine - March 2017 - 67
IEEE Electrification Magazine - March 2017 - 68
IEEE Electrification Magazine - March 2017 - 69
IEEE Electrification Magazine - March 2017 - 70
IEEE Electrification Magazine - March 2017 - 71
IEEE Electrification Magazine - March 2017 - 72
IEEE Electrification Magazine - March 2017 - 73
IEEE Electrification Magazine - March 2017 - 74
IEEE Electrification Magazine - March 2017 - 75
IEEE Electrification Magazine - March 2017 - 76
IEEE Electrification Magazine - March 2017 - 77
IEEE Electrification Magazine - March 2017 - 78
IEEE Electrification Magazine - March 2017 - 79
IEEE Electrification Magazine - March 2017 - 80
IEEE Electrification Magazine - March 2017 - Cover3
IEEE Electrification Magazine - March 2017 - Cover4
https://www.nxtbook.com/nxtbooks/pes/electrification_december2022
https://www.nxtbook.com/nxtbooks/pes/electrification_september2022
https://www.nxtbook.com/nxtbooks/pes/electrification_june2022
https://www.nxtbook.com/nxtbooks/pes/electrification_march2022
https://www.nxtbook.com/nxtbooks/pes/electrification_december2021
https://www.nxtbook.com/nxtbooks/pes/electrification_september2021
https://www.nxtbook.com/nxtbooks/pes/electrification_june2021
https://www.nxtbook.com/nxtbooks/pes/electrification_march2021
https://www.nxtbook.com/nxtbooks/pes/electrification_december2020
https://www.nxtbook.com/nxtbooks/pes/electrification_september2020
https://www.nxtbook.com/nxtbooks/pes/electrification_june2020
https://www.nxtbook.com/nxtbooks/pes/electrification_march2020
https://www.nxtbook.com/nxtbooks/pes/electrification_december2019
https://www.nxtbook.com/nxtbooks/pes/electrification_september2019
https://www.nxtbook.com/nxtbooks/pes/electrification_june2019
https://www.nxtbook.com/nxtbooks/pes/electrification_march2019
https://www.nxtbook.com/nxtbooks/pes/electrification_december2018
https://www.nxtbook.com/nxtbooks/pes/electrification_september2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2018
https://www.nxtbook.com/nxtbooks/pes/electrification_december2017
https://www.nxtbook.com/nxtbooks/pes/electrification_september2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2017
https://www.nxtbook.com/nxtbooks/pes/electrification_june2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2016
https://www.nxtbook.com/nxtbooks/pes/electrification_september2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2016
https://www.nxtbook.com/nxtbooks/pes/electrification_march2015
https://www.nxtbook.com/nxtbooks/pes/electrification_june2015
https://www.nxtbook.com/nxtbooks/pes/electrification_september2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2014
https://www.nxtbook.com/nxtbooks/pes/electrification_june2014
https://www.nxtbook.com/nxtbooks/pes/electrification_september2014
https://www.nxtbook.com/nxtbooks/pes/electrification_december2014
https://www.nxtbook.com/nxtbooks/pes/electrification_december2013
https://www.nxtbook.com/nxtbooks/pes/electrification_september2013
https://www.nxtbookmedia.com