Siemens SINAMICS S120, Function Manual

Page: 165 / 1094

Servo control
4.15 Vdc control
Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
165
4.15 Vdc control
Principle
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
mot
of the Motor Module from the DC link is given by
P
mot
= V
DC, actual value
· (V
DC, actual value
- p1248) · p1250
Correspondingly, a maximum regenerative feedback power P
gen
of the Motor Module into the
DC link of
P
gen
= V
DC, actual value
· (p1244 - V
DC, actual value
) · p1250
The V
dc
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 · 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
dc
controller can be used, for example, when a Line Module without energy feedback
capability (V
dc_max
controller) is used and as a safety measure in the event of a power failure
(V
dc_min
and V
dc_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 V
dc
control also have an impact on V/f control, although the
dynamic response of V
dc
control is slower in this case.