Siemens SINAMICS S120 Function Manual page 266

U/f control (vector control)
5.4 Vdc control
Vdc_min control
Figure 5-8
In the event of a power failure, Vdc_min control is activated when the Vdc_min switch-on
level is undershot. This controls the DC-link voltage and maintains it at a constant level. The
motor speed is reduced.
When the line supply returns, the DC-link voltage increases again. 5% above the Vdc_min
switch-on level, the Vdc_min control is switched off again. The motor continues operating
normally.
If the power supply is not re-established, the motor speed continues to drop. When the
threshold in p1297 is reached, this results in a response in accordance with p1296.
Once the time threshold (p1295) has elapsed without the line voltage being re-established, a
fault is triggered (F07406), which can be parameterized as required (factory setting: OFF3).
The Vdc_min controller can be activated for a drive. Other drives can participate in
supporting the DC link, by transferring to them a scaling of their speed setpoint from the
controlling drive via BICO interconnection.
Note
If a voltage recovery is expected, you must make sure that the converter is not disconnected
from the line supply. It could become disconnected, for example, if the line contactor drops
out. The line contactor must be supplied, e.g. from an uninterruptible power supply (UPS).
264
Switching Vdc_min control on/off (kinetic buffering)
Function Manual, (FH1), 01/2013, 6SL3097-4AB00-0BP3
Drive functions