Vdc Control - Siemens SINAMICS S120 Function Manual

Servo control

3.14 Vdc control

3.14 Vdc control
Description
Vdc control can be activated if overvoltage or undervoltage is present in the DC link line-up.
In the line-up, one or more drives can be used to relieve the DC link. This prevents a fault
from occurring due to the DC link voltage and ensures that the drives are always ready to
use
This function is activated by means of the configuration parameter (p1240). It can be
activated if an overvoltage or undervoltage is present. The torque limits of the motors at
which the Vdc controller is active can be affected if discrepancies in the DC link voltage are
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.
106
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
Drive functions