Siemens SINAMICS S120 Function Manual page 144

Operating Modes
Vector control
Description of Vdc_min control
V
controller
dc
active
Fig. 3-38
In the event of a power failure, Vdc_min control is activated when the Vdc_min
switch-in level is undershot. This controls the DC link voltage and maintains it at a
constant level. The motor speed is reduced.
When the power supply is restored, the DC link voltage increases again and
Vdc_min control is deactivated at 5 % above the Vdc_min switch-on level. The mo-
tor continues operating normally.
If the power supply is not reestablished, the motor speed continues to drop. When
the threshold in p1257 is reached, this results in a response in accordance with
p1256.
Once the time threshold (p1255) has elapsed without the line voltage being reesta-
blished, a fault is triggered (F07406), which can be parameterized as required (fac-
tory setting: OFF3).
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.
3-144
Power failure
r1286
without KIB fault
F30003
0.00V
1
0
n
setp
RPM
I
qsetp
Motor
0 A
Switching Vdc_min control on/off (kinetic buffering)
Power restore
without power restore fault F7405
T
Power failure
regenerative
© Siemens AG 2006 All Rights Reserved
SINAMICS S120 Function Manual, 03/2006 Edition
t
t
t
t