Siemens SINAMICS S120 Function Manual page 142

Vector control
4.9 Vdc control
The "Vdc control" function can be activated using the appropriate measures if an overvoltage
or undervoltage is present in the DC link.
● Overvoltage in the DC link
● Undervoltage in the DC link
Properties
● Vdc control
● Vdc_max control
● Vdc_min control (kinetic buffering)
142
– Typical cause
The drive is operating in regenerative mode and is supplying too much energy to the
DC link.
– Remedy
Reduce the regenerative torque to maintain the DC link voltage within permissible
limits. With the Vdc controller activated, the converter may automatically extend the
ramp down time of a drive if the shutdown supplies too much energy to the DC link.
– Typical cause
Failure of the supply voltage or supply for the DC link.
– Remedy
Specify a regenerative torque for the rotating drive to compensate the existing losses,
thereby stabilizing the voltage in the DC link (kinetic buffering).
– This comprises Vdc_max control and Vdc_min control (kinetic buffering), which are
independent of each other.
– Joint PI controller. The dynamic factor is used to set Vdc_min and Vdc_max control
independently of each other.
– This function can be used to control momentary regenerative load without shutdown
using "overvoltage in the DC link".
– Vdc_max control is only recommended with a supply without active closed-loop control
for the DC link and without feedback.
– With this function, the kinetic energy of the motor is used for buffering the DC link
voltage in the event of a momentary power failure, thereby delaying the drive.
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
Drive functions