Siemens SINAMICS S120 Function Manual page 170

Servo control
5.17 Vdc control
V control
dc_min
Figure 5-26
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 V
voltage threshold of p1248 is fallen below, these drives are switched into the generator mode
so that they can buffer the DC link voltage with their kinetic energy. The threshold should be set
considerably higher than the shutdown threshold of the Motor Modules (recommendation: 50
V below the DC link voltage). When the line supply returns, the V
inactive. The drives approach the speed setpoint again. If the line supply does not return, then
the DC link voltage collapses as soon as the kinetic energy of the drives is exhausted with an
active V
Note
If it is expected that the line supply will return, you must make sure that the drive lineup is not
disconnected from the line supply. It could become disconnected, for example, if the line
contactor drops out. The line contactor must be supplied, e.g. from an uninterruptible power
supply (UPS).
V control without braking
dc_min
As for V
the DC link voltage (p1240 = 8, 9). The effective upper torque limit must not be less than the
torque limit offset (p1532). The motor does not go into the generator mode and does not draw
any active power from the DC link.
168
Switching V
dc_min
controller can be activated for one or more drives (p1240 = 2, 3). When the set
dc_min
controller.
dc_min
control with braking, however, active motor braking can be prevented by reducing
dc_min
control on/off (kinetic buffering)
controller is automatically
dc
Function Manual, 06/2019, 6SL3097-5AB00-0BP2
Drive functions