Environmental Engineering Reference
In-Depth Information
Power electronics - 2nd group
(
V
f
,
I
f
)
2
6
4
2
V
b
5
2
Control electronics
Cmds
3
Controller, Comm.
gate drives, Pwr supply
1
4
6
1
3
5
(
V
f
,
I
f
)
1
Power electronics - 1st group
Figure 5.41 Electronic pole change technique for 2:1 speed range increase
2:1 pole change must be somewhat larger than a 4-pole rotor in order to remain
unsaturated under 2-pole operation.
Electronic pole changing of an existing IMdesign often leads to oversaturation of
the machine's stator yoke (back iron) or rotor yoke. This is the case because a high pole
number machine is often reconfigured electronically to a lower pole number machine -
in the case of the electronic pole changing scheme covered here, by a factor of 2:1. In
order to realize pole change of 3:1 or in fact arbitrary pole number changing, the
techniques of PPM must be employed as will be seen in the next section [32].
Before closing this topic on electronic pole changing by a factor of 2:1, con-
sider the impacts on the IM as illustrated in Figure 5.42. A 4-pole IM is electro-
nically changed to a 2-pole IM by redirecting the stator currents by appropriate
commands (Table 5.8).
Table 5.8 Electronic pole changing technique
Ref. current
4-pole
2-pole
Inverter group 1
i
1
i
a
i
a
i
3
i
b
i
c
i
5
i
c
i
b
Inverter group 2
i
2
i
a
i
a
i
4
i
b
i
c
i
6
i
c
i
b
