Vdc Control - Siemens SINAMICS S120 Function Manual

3.1.14

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_min 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 in-
dividual drives if there is a problem with the DC link.
© Siemens AG 2006 All Rights Reserved
SINAMICS S120 Function Manual, 03/2006 Edition
Operating Modes
Servo control
3-113