Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
297
V/f control (vector control)
The V/f control characteristic is the simplest way to control an induction motor. When
configuring the drive using the STARTER commissioning tool, V/f control is activated in the
"Closed-loop control structure" screen (also see p1300).
Note
For V/f control, the permissible range of the ratio between the rated motor current (p0305)
and rated Motor Module current (r0207) is 1:1 to 1:12.
The stator voltage of the induction motor is set proportional to the stator frequency. This
procedure is used for many standard applications where the dynamic performance
requirements are low, for example:
● Pumps
● Fans
● Belt drives
V/f control aims to maintain a constant flux Φ in the motor whereby the flux is proportional to
the magnetizing current (Iµ) or the ratio of voltage (V) to frequency (f).
Φ ∼ Iµ ∼ V/f
The torque M generated by an induction motor is proportional to the product of the flux and
current (the vector product Φ · I).
M ∼ Φ · I
To generate as much torque as possible with a given current, the motor must function using
the greatest possible constant flux. To maintain a constant flux (Φ), therefore, the voltage (V)
must be changed in proportion to the frequency (f) to ensure a constant magnetizing current
(Iµ). V/f characteristic control is derived from these basic premises.
Figure 6-1 Operating areas and characteristic curves for the induction motor with converter supply
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