Siemens SINAMICS G120 Operating Instructions Manual page 357

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.
Figure 8-84
There are several versions of the V/f characteristic as shown in the table below.
Control Units CU240S
Operating Instructions, 11/2006, A5E00766042B AA
Operating ranges and characteristics of an induction motor when fed from an inverter
8.24 Open-loop and closed-loop control
Functions
8-161