Siemens SINAMICS S120 Function Manual page 103

significant enough. The motors may no longer be able to maintain their setpoint speed or the
acceleration/braking phases are prolonged.
The Vdc controller is an automatic 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 via the configuration
parameter (p1240).
The recommended setting for the P gain is
p1250 = 0.5*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
(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.
Description of Vdc_min control (p1240 = 2, 3)
Figure 3-21
In the event of a power failure, the Line Module can no longer supply the DC link voltage,
particularly if the Motor Modules in the DC link line-up are drawing active power. To maintain
the DC link voltage in the event of a power failure (e.g. for a controlled emergency
retraction), the Vdc_min controller can be activated for one or more drives. If the voltage
threshold set in p1248 is undershot, these drives are decelerated so that their kinetic energy
Drive Functions
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
Switching Vdc_min control on/off (kinetic buffering)
Servo control
3.14 Vdc control
103