Automotive Engineering - December 2023 - BET-12

Battery Modeling
Motor Efficiency at 20 °C, Numerical
0.36
0.34
0.32
0.3
0.28
0.26
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
200
65
55
50
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400
Rotational speed (rpm)
Figure 5. An efficiency map from a parametric simulation. The numbers labeled in the map (65, 75,
and 85) refer to the color scale shown on the right. (Image: COMSOL)
Campbell Diagram, First Microphone
4000
3500
55
3000
2500
2000
45
1500
40
1000
35
500
55
1000
2000
3000
4000
5000
Revolutions (RPM)
Figure 6. A Campbell diagram for analyzing motor frequency. This plot focuses on a given microphone
position. Each line represents a harmonic, and on the color scale, red represents louder
noise. (Image: COMSOL)
Determining Losses,
Temperature Rise, and Cooling
Solutions
Once the optimal iron thickness is determined,
it is time to calculate the iron
and copper losses. An increase in speed
(and the consequent losses) can make it
difficult to keep a motor cool, which will
cause a motor to reach its thermal limit.
When this spike in motor temperature
occurs, the motor flux density can de12
crease,
having a domino effect on the
torque and overall efficiency. For these
reasons, one should look at iron and copper
losses first, and then at temperature
rise and cooling solutions.
Iron losses occur due to time-varying
magnetic flux density and they include
hysteresis and eddy current losses.
Copper losses, on the other hand, happen
because of conduction current flow,
and they include ohmic losses within
6000
7000
8000
9000
10000
30
-65.5
Analyzing an Efficiency Map
The data collected thus far can be
combined and accounted for in an
efficiency map (Figure 5), which
shows the efficiency as a function of
speed and torque. This makes it possible
to first estimate the overall
energy used by a motor during a
complete drive cycle and then to
deduce the range of the vehicle after
a single charge for a given battery
size. Given that an EV motor's marketability
depends on how well it
utilizes electrical power, it is safe to
say that taking the time to create an
efficiency map is worthwhile.
Efficiency maps use color and contour
to help visualize the efficiency. In Figure
5, the blue, yellow, and green regions
have low efficiency, and the vehicle altogether
consumes less power at the low
speed or low torque points as compared
to the red region, where both speed and
torque are high.
Battery & Electrification Technology, December 2023
50
56.9
60
90
85
80
75
85
70
65
75
60
55
the stator coil. Both types of losses
can be calculated in the COMSOL
Multiphysics® software. The software
offers a built-in feature for loss calculation
as well as features for creating
plots of the losses and their important
characteristics, such as how they
vary as functions of both speed and
current amplitude.
From there, it is useful to compute
the losses in combination with heat
transfer phenomena using simulation
software. This makes it possible
to visualize how much the motor
will rise in temperature and how
different forms of cooling, such as
forced or natural air convection or
forced water cooling, can help subdue
it. Obtaining a visualization of
these conditions will help in determining
the needed insulation class.
For example, assume that for the
model shown here, forced air convection
is the preferred method.
When forced convection with 1 m/s
flow velocity is applied to the model,
the results indicate that the most
beneficial insulation class in this
case would be 130 (B), which means
that 130 °C would be the maximum
hot spot temperature for the design
(Figure 4).
Frequency (Hz)
Average rotor torque (N.m)

Automotive Engineering - December 2023

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