Rockwell Automation 20B PowerFlex 700 AC Drives Vector Control (v4.001 and up) - Manual (Page 117)

Rockwell Automation Publication 20B-UM002G-EN-P - July 2014 117
Application Notes Appendix C
2. The drive will then provide the motor with flux as well as perform a check
for current flow through all three motor phases. This ensures that torque
will be delivered to the load when the mechanical brake is released. When
torque proving is enabled, open phase loss detection is performed
regardless of the setting of Bit 12 of [Fault Config 1], parameter 238.
3. If the drive passes all tests, the brake will be released and the drive will take
control of the load after the programmed time in [Brk Release Time],
parameter 604 which is the typical mechanical release time of the brake.
Brake Proving
When the drive receives a stop command to end a lifting operation, the following
actions occur:
1. The brake is commanded closed when the speed of the motor reaches zero.
2. After the time period programmed in [Brk Set Time], parameter 607, the
drive will verify if the brake is capable of holding torque. It will do this by
ramping the torque down at a rate set in [TorqLim SlewRate], parameter
608. Note that the drive can be started again at anytime without waiting
for either of the above timers to finish.
3. While the torque is ramping down, the drive will perform a brake slip test.
If movement exceeds the limit set in [BrkSlip Count], parameter 609, then
an alarm is set (32, Brake Slipped) and the drive will start a brake slip
procedure. The drive will allow the motor to travel the distance
programmed [Brk Alarm Travel], parameter 610. Another slip test will be
performed and will repeat continuously until; A) the load stops slipping,
or B) the load reaches the ground. This feature keeps control of the load
and returns it to the ground in a controlled manner in the event of a
mechanical brake failure.
Once a Brake Slipped alarm occurs, drive power must be cycled to clear the
alarm and re-start the drive.
Speed Monitoring / Speed Band Limit
This routine is intended to fault the drive if the difference between the speed
reference and the encoder feedback is larger than the value set in [Spd Dev Band],
parameter 602 and the drive is NOT making any progress toward the reference.
[SpdBand Integrat], parameter 603 sets the time that the speed difference can be
greater than the deviation band before causing a fault and setting the brake.
Float
Float is defined as the condition when the drive is holding the load at zero hertz
while holding off the mechanical brake. The float condition starts when the
frequency drops below the speed set in [Float Tolerance], parameter 606. Float
will stay active for a period of time set by [ZeroSpdFloatTime], parameter 605. If
a digital input (parameters 361…366) is set to “Micro Pos” (also Float) and it is
closed, the Float condition will stay active and will disregard the timer. This
signal is also available through a communication device, see [TorqProve Setup],
parameter 601.