Siemens SINAMICS S120 Function Manual page 115

Description of Vdc_max control (p1240 = 1, 3)
820 V
p1244
Fig. 3-23
With Infeed Modules without feedback or in the event of a power failure, the DC
link voltage can increase until it reaches the shutdown threshold when drives in the
DC link line-up are decelerated. To prevent the system from shutting down due to a
DC link overvoltage, the Vdc_max controller can be activated for one or more
drives. The Vdc_max controller is normally activated for drives that have to decele-
rate/accelerate high levels of kinetic energy themselves. When the overvoltage
threshold in p1244 is reached (recommended setting: 50 V higher than the DC link
voltage), the braking torque of the drives with an active Vdc_max controller is redu-
ced by shifting the torque limit. In this way, the drives feed back the same amount
of energy that is used as a result of losses or consumers in the DC link, thereby
minimizing the braking time. If other drives for which the Vdc_max controller is not
active feed energy back, the drives with an active Vdc_max controller can even be
accelerated to absorb the braking energy and, in turn, relieve the DC link.
Vdc controller monitoring functions
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 ensure that the DC link voltage is not burdened with uncritical drives in
the event of a power failure, these drives can be switched off by a fault with a para-
meterizable voltage threshold (p1248). This is carried out by activating the
Vdc_min monitoring function (p1240 = 5, 6).
In the event of a power failure, the DC link voltage can increase until it reaches the
shutdown threshold when drives are decelerated. To ensure that the DC link vol-
tage is not burdened with uncritical drives in the event of a power failure, these
drives can be switched off by a fault with a parameterizable voltage threshold
(p1244). This is carried out by activating the Vdc_max monitoring function (p1240
= 4, 6).
© Siemens AG 2006 All Rights Reserved
SINAMICS S120 Function Manual, 03/2006 Edition
[V]
without Vdc_max control
Fault F30002
V
DC link
|n|
I
qsetp
0 A
Switching-in/switching-out the Vdc_max control
Vdc_max
Vdc_thresh upper
n
act
n
setp
I
qsetp without Vdc_max control
Operating Modes
Servo control
t
3-115