Siemens SINAMICS S120 Function Manual page 177

In the event of a power failure, Vdc_min control is activated when the Vdc_min switch-in 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 at 5 % above the Vdc_min switch-on level. The motor continues operating
normally.
If the power supply is not reestablished, 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 reestablished, 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 a scaling of their speed setpoint from the controlling
drive via BICO interconnection.
Note
You must make sure that the converter is not disconnected from the power supply. It could
become disconnected, for example, if the line contactor drops out. The line contactor should
have an uninterruptible power supply (UPS), for example.
Description of Vdc_max control
Figure 5-8
The switch-in level for Vdc_max control (r1282) is calculated as follows:
● When the function for automatically detecting the switch-on level is switched off
● When the function for automatically detecting the switch-on level is switched on
Drive Functions
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
Switching Vdc_max control on/off
(p1294 = 0)
r1282 = 1.15 * p0210 (device connection voltage, DC link).
(p1294 = 1)
r1282 = Vdc_max - 50 V (Vdc_max: overvoltage threshold of the Motor Module)
Vector V/f control (r0108.2 = 0)
5.4 Vdc control
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