Vdc Control - Siemens SINAMICS S120 Function Manual

Servo control

3.14 Vdc control

3.14 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
P
mot
Correspondingly, a maximum regenerative feedback power Pgen of the Motor Module into
the DC link of
P
gen
The Vdc 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 x 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
capability (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.
The voltage limit values for Vdc control also have an impact on V/f control, although the
dynamic response of Vdc control is slower in this case.
134
= V x (V
DC, actual value DC, actual value
= V x (p1244 - V
DC, actual value
of the Motor Module from the DC link is given by
mot
- p1248) x p1250
) x p1250 is obtained
DC, actual value
Function Manual, (FH1), 01/2013, 6SL3097-4AB00-0BP3
Drive functions