Automotive Engineering - December 2023 - BET-10

Battery Modeling
Permanent
magnets
Stator iron
Stator coils
Rotor iron
Stainless steel
Continuity
boundary
Figure 2. Example model of a 10-pole PM motor with 12 slots. (Image: COMSOL)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
05 10
15
20
Rotor angle (°)
Figure 3. A plot showing variations of the example motor's rotor torque and iron thickness.
(Image: COMSOL)
mm
degC
20
15
10
5
108.35
-5
-10
-15
-20
-30-20
-100 10
20
mm
Figure 4. The temperature results when forced air convection with 1 m/s flow velocity is
applied. (Image: COMSOL)
10
25
Iron thickness = 1 mm
Iron thickness = 2 mm
Iron thickness = 3 mm
30
35
net torque that converts the stator winding
currents into mechanical power. A
maximum amount of mechanical torque
needs to be exerted on the rotor so that
it will rotate with as much force as the
engineer wants, and in the direction they
want. All of this considered, the engineer
will want to determine whether the current
loading is maintainable or too high,
as having a too-high current loading will
cause the core material to go into heavy
saturation, which will result in a decline
of mechanical power.
The best way to examine the current
loading and torque is by testing the
model setup. To better visualize the topics
discussed here, consider a 10-pole PM
machine with 12 slots (Figure 2).
Because the torque relies on the synchronization
of the magnetic fields produced
by the rotor and the stator, the
optimum angle offset between the rotor
and stator fields must be determined. The
offset angle can be found by either rotating
the rotor with an angular span corresponding
to an electrical period or by
cycling the stator current through an
electrical period, with the rotor at rest.
Once the optimum angle offset is determined,
the engineer can begin investigating
ways to improve efficiency and save
material use. There are of course many
ways one can do this, but here, we will discuss
one method: examining the dependency
between the stator iron material,
current loading, and torque output. This
can be found by analyzing the thickness of
the iron core and its impact on efficiency.
The engineer should simulate different
variants of iron thickness, focusing on the
effects that each level of thickness has
on the rotor torque. By doing this, an iron
thickness value that maintains optimal
torque and stays within size (compactness),
weight, and pricing restrictions or
goals can be determined.
For the example motor seen in Figure
2, it is found that the optimal iron thickness
is 2 mm; using a thickness under
this value will negatively impact the
torque. For example, as seen in Figure 3,
a thickness of 1 mm resulted in lower
torque. Going thicker than 2 mm, however,
is not the optimal solution, as it requires
an increase in material and therefore
increases in weight and cost without
a substantial increase in torque.
Battery & Electrification Technology, December 2023
Rotor torque (N.m)

Automotive Engineering - December 2023

Table of Contents for the Digital Edition of Automotive Engineering - December 2023