Siemens Sinamics S120 Function Manual page 117

The Vdc controller is a P controller that influences the torque limits. It only intervenes when
the DC link voltage approaches the "upper threshold" (p1244) or "lower threshold" (p1248)
and the corresponding controller is activated with p1240.
The recommended setting for the P gain is
p1250 = 0.5 x DC link capacitance [mF].
Once the DC link has been identified (p3410), the DC link capacitance can be read in
parameter p3422 in the Infeed Module.
Note
To ensure that the drives remain active if the Line Module has failed, the response to fault
F07841 must be changed to "none" or the operation message from the Infeed Module must
be permanently set to "1" with p0864.
The Vdc controller can be used, for example, when a Line Module without energy feedback
capability (Vdc_max controller) is used and as a safety measure in the event of a power
failure (Vdc_min and Vdc_max controller). To ensure that critical drives can be operated for
as long as possible, parameterizable faults exist that switch off individual drives if there is a
problem with the DC link.
The voltage limit values for Vdc control also have an impact on V/f control, although the
dynamic response of Vdc control is slower in this case.
Description of Vdc_min control (p1240 = 2, 3)
Figure 3-23
Drive functions
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Switching Vdc_min control on/off (kinetic buffering)
Servo control
3.14 Vdc control
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