Vdc Control - Siemens SINAMICS S120 Function Manual

5.17

Vdc control

Function description
The Vdc control monitors the DC voltage in the DC link for overvoltage and undervoltage. If an
overvoltage or undervoltage is identified in the DC link line-up, a subsequent response can be
set with the Vdc control via p1240.
The torque limits of the motors for 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.
In a drive line-up, one or more drives can be used to relieve or support the DC link. This allows
a fault due to an unfavorable DC link voltage to be avoided. The drives remain ready for
operation.
Generally, a maximum motoring power p
● P
Correspondingly, a maximum regenerative feedback power P
DC link of:
● P
The V
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 · 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 V
capability (V
(V
dc_min
possible, parameterizable faults exist that switch off individual drives if there is a problem with
the DC link.
The voltage limit values for V
response of V
Drive functions
Function Manual, 06/2019, 6SL3097-5AB00-0BP2
= V · (V
mot DC, actual value DC, actual value
= V · (p1244 - V
gen DC, actual value
controller is a P controller that influences the torque limits. It only intervenes when the
dc
controller can be used, for example, when a Line Module without energy feedback
dc
controller) is used and as a safety measure in the event of a power failure
dc_max
and V controller). To ensure that critical drives can be operated for as long as
dc_max
control is slower in this case.
dc
of the Motor Module from the DC link is given by:
mot
- p1248) · p1250
) · p1250
DC, actual value
control also have an impact on U/f control, merely the dynamic
dc
Servo control
5.17 Vdc control
of the Motor Module into the
gen
167