Environmental Engineering Reference
In-Depth Information
p
U
oc phase
w
e
p
ð
150
=
p
Þ
2,094
y
m
¼
¼
¼
0
:
058 Wb-t
(c) At
V
WOT
the line-to-line voltage of MG1 is
P
2
g
fd
k
E2
r
w
4
ð
3
:
542
Þð
2
:
478
Þ
0
:
355
w
MG2 WOT
¼
V
WOT
¼
ð
59
:
3
Þ
¼
5,863 rad
=
s
r
3
2
U
oc
WOT
¼ w
MG2 WOT
y
m
¼
5,863
ð
0
:
058
Þ
¼
416
:
5V
rms
(d) Recalling the relationship for B(H) from Exercise 1, and referring to figure 5.1,
then the B-H characteristics given the fact that this NdFeB magnet has
B
r
¼
1.19 T,
H
ci
¼
14.46 kO
e
at moderate operating temperature and for the specifics
of the magnet stated the static permeance coefficient,
P
c
, can be found, and
from this an approximation of airgap flux density,
B
g
¼
B
m
.
¼
A
g
A
m
L
m
g
6
:
6
0
:
733
ð<
1
Þ
5
P
c
P
c
P
c
þ m
rec
B
r
¼
5
6
:
05
1
:
19
¼
0.98
ð
T
Þ
B
g
¼
In part (d), there are approximations based on geometry and leakage factors
influencing the IPM magnet flux that are outside the scope of this text. Suffice to
say that leakage due to magnet end effects, flux shunting via magnet pocket bridges
and other non-ideal factors all act to decrease the permeance coefficient - the goal
of course being to realize as high an airgap flux density as possible.
More is discussed on this topic of IPM electric machines in the exercises at the
end of this chapter. The reader is advised to consider these reinforcements on the
topics discussed here.
5.3.2 Flux squeeze
It is somewhat misleading that the flux squeeze rotor geometry is believed by many
to be superior to the buried magnet design. This is true, but for some very restricted
applications to be discussed shortly. The flux squeeze design appears tailored to
ceramic magnets because the large magnet faces are available to force significant
levels of flux density in the machine airgap. Figure 5.24 illustrates the flux paths in
the flux squeeze geometry.
