Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 247)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 247
Motor Control Chapter 4
Regen Power Limit The P426 [Regen Power Lmt] is programmed as a percentage of the rated power.
The mechanical energy that is transformed into electrical power during a
deceleration or overhauling load condition is clamped at this level. Without the
proper limit, a bus overvoltage can occur. When using the bus regulator [Regen
Power Lmt] can be left at factory default, -50%.
When using dynamic braking or a regenerative supply, [Regen Power Lmt] can be
set to the most negative limit possible (–800%). When you have dynamic braking
or regenerative supply, but want to limit the power to the dynamic brake or
regenerative supply, [Regen Power Lmt] you can set a specific level. Values in this
parameter are valid only in a Flux Vector mode.
The following series of plots describes the difference between changing Regen
Power Limit versus changing the Negative Torque Limit. The beginning part of
every plot is identical, this is the acceleration of the motor. Once the stop is
commanded and deceleration begins, note the red trace in each. This represents
torque current. Because power is proportional to speed, as the speed decreases,
the torque current increases allowing more power to be dissipated.
Note the speed feedback in the RPL = -20%, the slower the motor gets the faster
it’s brought to zero speed and the torque current increases. The higher the value
in Regen Power Limit the more power is allow to pass through.
Focus on the torque current (red) trace as you scroll through the plots and note
the change in the shape as the regen power limit was increase. Then see how it is
clamped at a particular level when Negative Torque Limit is changed.
RPL = -20%
DC Bus Voltage Iq TrqRef P685 Motor Speed
DB Active