Siemens CU240B-2 - Kinetic Buffering (VDC Min Control)

Advanced commissioning
6.7 Application-specific functions
Converter with the CU240B-2 and CU240E-2 Control Units
304 Operating Instructions, 01/2016, FW V4.7 SP6, A5E34259001B AC
6.7.7
Kinetic buffering (Vdc min control)
Kinetic buffering increases the drive availability. The kinetic buffering utilizes the kinetic
energy of the load to buffer line dips and failures. During a line dip, the inverter keeps the
motor in the switched-on state for as long as possible. One second is a typical, maximum
buffer time.
Preconditions
The following prerequisites must be fulfilled to practically use the "kinetic buffering" function:
● The driven load has a sufficiently high inertia.
● The application allows a motor to be braked during a power failure.
Function
When the line supply dips or is interrupted, the DC link voltage in the inverter decreases. At
an adjustable threshold, kinetic buffering intervenes (V
DC min
control). The V
DC min
control
forces the load to go into slightly regenerative operation. As a consequence, the inverter
covers its power loss and the losses in the motor with the kinetic energy of the load. The
load speed decreases; however, during kinetic buffering, the DC voltage remains constant.
After the line supply returns, the inverter immediately resumes normal operation.
Image 6-52 Principle mode of operation of kinetic buffering