Siemens SINAMICS S120 Function Manual page 143

The "Vdc control" function can be activated using the appropriate measures if an
overvoltage or undervoltage is present in the DC link.
S Overvoltage in the DC link
– 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.
S Undervoltage in 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).
Properties
S Vdc control
– 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.
S Vdc_max control
– This function can be used to control momentary regenerative load without
shutdown with "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.
S Vdc_min control (kinetic buffering)
– 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.
© Siemens AG 2006 All Rights Reserved
SINAMICS S120 Function Manual, 03/2006 Edition
Operating Modes
Vector control
3-143