Rockwell Automation 20A PowerFlex 70EC/700VC - Manual (Page 116)

112 Stop Modes
Test Example for Fast Braking
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 will provide more braking torque without causing the drive to regenerate.
1. On Stop, the drive output will decrease 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 will not occur. This causes
excess energy to be lost in the motor.
2. The method uses a PI based bus regulator to regulate the bus voltage to a reference (e.g. 750V) by automatically
decreasing output frequency at the proper rate.
3. 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 will be used to complete the stop if the DC Braking Time is non-zero, then the
output is shut off.
4. Use of the current regulator ensures that over current trips don’t occur and allow for an easily adjustable and
controllable level of braking torque.
5. 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.
6. Important: For this feature to function properly the active Bus Reg Mode A or B must be set to Adjust “Freq” and NOT
be “Disabled”.
Mode Description
Stop
Command
Time
Output Voltage
Output Current
Motor Speed
Bus Voltage
Command Speed
Bus Voltage
Motor Speed
Feedback
Commanded
Frequency
DC Brake Current
(Near Zero Speed)
Motor Current