Efficient Networks Siemens Sinamics S120 - Manual (Page 169)

Drive Functions
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
169
Vector V/f control (r0108.2 = 0)
5
5.1 Introduction
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 applications with low
dynamic requirements, such as:
● Pumps and fans
● Belt drives
and other similar processes.
V/f control aims to maintain a constant flux Φ in the motor. whereby the flux is proportional to
the magnetization current (Iµ) or the ratio of voltage (U) to frequency (f).
Φ ∼ Iµ ∼ V/f
The torque (M) generated by the induction motors is, in turn, proportional 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 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 magnetization
current (Iµ). V/f characteristic control is derived from these basic premises.
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Figure 5-1 Operating areas and characteristic curves for the induction motor with converter supply
Several variations of the V/f characteristic exist, which are shown in the following table: