Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 101)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 101
Drive Configuration Chapter 1
Fast Brake
This method takes advantage of the characteristic of the induction motor
whereby frequencies greater than zero (DC braking) can be applied to a spinning
motor that provides more braking torque without causing the drive to regenerate:
• On Stop, the drive output decreases based on the motor speed, keeping the
motor out of the regen region. This is accomplished by lowering the
output frequency below the motor speed where regeneration does not
occur. This causes excess energy to be lost in the motor.
• The method uses a PI based bus regulator to regulate the bus voltage to a
reference (that is 750V) by automatically decreasing output frequency at
the proper rate.
• When the frequency is decreased to a point where the motor no longer
causes the bus voltage to increase, the frequency is forced to zero. DC
brake is used to complete the stop if the DC Braking Time is non-zero,
then the output is shut off.
• Use of the current regulator verifies that over current trips don’t occur and
allow for an easily adjustable and controllable level of braking torque.
• Use of the bus voltage regulator results in a smooth, continuous control of
the frequency and forces the maximum allowable braking torque to be
utilized at all times.
IMPORTANT For this feature to function properly the active [Bus Reg Mode A/B] must be
set to 1 “Adjust Freq” and not be 0 “Disabled.”
Bus Voltage
Output Voltage
Output Current
Motor Speed
Command Speed
Time
Stop Command