6.8.3 Kinetic buffering (Vdc min control)
Overview
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 converter keeps the motor in the
switched-on state for as long as possible. One second is a typical maximum buffer time.
Precondition
The following conditions have to be fulfilled to use the "kinetic buffering" function
advantageously:
● The driven machine has a sufficiently high inertia.
● The application allows a motor to be braked during a power failure.
Function description
When the line supply dips, the DC-link voltage in the converter decreases. The kinetic buffering
(V
DC min
control) intervenes at an adjustable threshold. The V
DC min
control forces the load to go
into slightly regenerative operation. As a consequence, the converter covers its power loss and
the losses in the motor with the kinetic energy of the load. The load speed decreases, but the
DC-link voltage remains constant during the kinetic buffering. After the line supply returns, the
converter immediately resumes normal operation.
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Figure 6-77 Principle mode of operation of kinetic buffering
Parameters
Number Name Factory setting
r0056[0…15] CO/BO: Status word, closed-loop control -
p0210 Device supply voltage 400 V
p1240[D] Vdc controller configuration (vector control) 1
Advanced commissioning
6.8 Drive availability
SINAMICS G120XA converter
Operating Instructions, 03/2019, FW V1.0, A5E44751205B AB 323
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