Siemens SINAMICS S120 - Page 308

V/f control (vector control)
6.5 Vdc control
Drive functions
308 Function Manual, 11/2017, 6SL3097-4AB00-0BP5
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.
Properties
● V
dc
control
– This comprises V
dc_max
control and V
dc_min
control (kinetic buffering). These two
functions can be parameterized independently of one another and activated.
– There is a common PID controller. The dynamic factor is used to set V
dc_min
and V
dc_max
control to a smoother or harder setting independently of each other.
● V
dc_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.
● V
dc_max
control
– This function can be used to control momentary regenerative load without shutdown
using "overvoltage in the DC link".
– V
dc_max
control is only recommended with a supply without active closed-loop control
for the DC link and without feedback.
Vdc_min control
Figure 6-8 Switching V
dc_min
control on/off (kinetic buffering)
In the event of a power failure, V
dc_min
is activated when the V
dc_min
switch-on level is
undershot. This controls the DC link voltage and maintains it at a constant level. The motor
speed is reduced.