Environmental Engineering Reference
In-Depth Information
Another recent variant on the IPM has been a novel rearrangement of the
permanent magnets to reside in cavities that closely resemble the pattern of a
wound field synchronous machine. The rotor continues to have magnet cavities and
iron bridges to support the structure. Figure 5.28 illustrates this unique design
referred to as a permanent magnet reluctance machine (PRM). Magnet flux in the
PRM follows a high reluctance path as it does in the normal IPM, but
q
-axis flux
from the stator follows an iron path through the rotor so that there is a cross-field in
the rotor laminations.
S
N
N
S
S
N
N
S
S
N
N
S
N
N
S
S
Figure 5.28 Permanent magnet reluctance machine
In the PRM, the combination of permanent magnet torque and reluctance tor-
que are suitable for hybrid propulsion systems. This can be seen from the fact that
conventional IPM machines require substantial
d
-axis current to realize field
weakening, but the PRM realizes flux control with an inverse relationship of stator
current to achieve the same results. This rather obscure behaviour can be seen by
comparison of
d
-axis currents in the plot of voltage versus speed for both no load
and full load conditions shown in Figure 5.29.
PRM
IPM
U
oc
U
load
U
load
I
d
U
oc
I
d
Speed
Speed
Figure 5.29 Illustration of
d
-axis current behaviour in PRM versus IPM
