Siemens SINAMICS S120 Function Manual page 197

Vdc_min control
Figure 4-15
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 power supply is restored, the DC-link voltage increases again and Vdc_min control
is deactivated again at 5% above the Vdc_min switch-on level. The motor continues
operating normally.
If the power supply is not re-established, the motor speed continues to drop. When the
threshold in p1257 is reached, this results in a response in accordance with p1256.
Once the time threshold (p1255) 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 drive line-up 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).
Drive functions
Function Manual, (FH1), 01/2013, 6SL3097-4AB00-0BP3
Switching Vdc_min control on/off (kinetic buffering)
Vector control
4.10 Vdc control
195