Vector V/F Control (R0108.2 = 0) - Siemens SINAMICS S120 Function Manual

Operating Modes

Vector V/f control (r0108.2 = 0)

3.3 Vector V/f control (r0108.2 = 0)
The simplest solution for a control procedure is the V/f curve, whereby the stator
voltage for the induction motor or synchronous motor is controlled proportionately
to the stator frequency. This method has proved successful in a wide range of ap-
plications with low dynamic requirements, such as:
S Pumps and fans
S Belt drives
and other similar processes.
V/f control aims to maintain a constant flux φ in the motor, whereby the flux is
proportionate to the magnetization current Iµ or the ratio of voltage (U) to
frequency (f).
φ ∼ Iµ ∼ U/f
The torque (M) generated by the induction motors is, in turn, proportionate to the
product (or, more precisely, the vector product φ x I) of the flux and current.
M ∼ φ x I
To generate as much torque as possible with a given current, the motor must func-
tion using the greatest possible constant flux. To maintain a constant flux (φ),
therefore, the voltage (V) must also be changed in proportion to the frequency (f)
to ensure a constant magnetization current (Iµ). V/f characteristic control is derived
from these basic premises.
V, M,
M ,
- -{}- -n
Fig. 3-39
Several variations of the V/f characteristic exist, which are shown in the following
table.
3-142
Φ
Φ
- -{}- -n
U
Voltage range
Operating areas and characteristic curves for the induction motor with converter
supply
U
Point
of motor
M, Φ
Field range
f f
- -{}- -n
max
© Siemens AG, 2005. All rights reserved
SINAMICS S120 Function Manual, 06/05 Edition
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