Siemens SINAMICS S120 Function Manual page 114

Operating Modes
Servo control
Description of Vdc_min control (p1240 = 2, 3)
0.9 * r0208
Fig. 3-22
In the event of a power failure, the Line Module can no longer supply the DC link
voltage, particularly if the Motor Modules in the DC link line-up are drawing active
power. To maintain the DC link voltage in the event of a power failure (e.g. for a
controlled emergency retraction), the Vdc_min controller can be activated for one
or more drives. If the voltage threshold set in p1248 is undershot, these drives are
decelerated so that their kinetic energy can be used to maintain the DC link vol-
tage. The threshold should be considerably higher than the shutdown threshold of
the Motor Modules (recommendation: 50 V below the DC link voltage). When the
power supply is reestablished, the Vdc controller is automatically deactivated and
the drives approach the speed setpoint again. If the power supply cannot be re-
established, the DC link voltage collapses if the kinetic energy of the drives is ex-
hausted with an active Vdc_min controller.
Note
You must make sure that the converter is not disconnected from the power supply.
It could become disconnected, for example, if the line contactor drops out. The line
contactor should have an uninterruptible power supply (UPS), for example.
3-114
Power failure
p1248
without Vdc_min control
Fault F30003
0.00V
n
setp
RPM
I
qsetp
motor
0 A
Switching Vdc_min control on/off (kinetic buffering)
Power restore
T
Power failure
regenerative
© Siemens AG 2006 All Rights Reserved
SINAMICS S120 Function Manual, 03/2006 Edition
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