Functions
8.24 Open-loop and closed-loop control
Control Units CU240S
Operating Instructions, 11/2006, A5E00766042B AA
8-161
Φ ~ Iμ ~ V/f
The torque M, developed by induction motors, is proportional to the product (precisely the
Vectorial product Φ x I) of flux and current.
M ~ Φ * I
In order to generate the highest possible torque from a given current, the motor must operate
with a constant flux which is as high as possible. In order to keep the flux Φ constant, when
frequency f changes, the voltage V must be changed in proportion so that a constant
magnetizing current Iμ flows. The V/f characteristic control is derived from these basic
principles.
I
803˓
83
0
Q
˓
Q
0˓
I
Q
I
PD[
83
5DWHGPRWRU
RSHUDWLQJSRLQW
Figure 8-84 Operating ranges and characteristics of an induction motor when fed from an inverter
There are several versions of the V/f characteristic as shown in the table below.
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