Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 98)

98 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 1 Drive Configuration
DC Brake
This method uses DC injection of the motor to Stop and/or hold the load. DC
Brake is selected by setting P370/371 [Stop Mode A/B] to 3 “DC Brake.” You
can also choose the amount of time the braking is applied and the magnitude of
the current used for braking with P395 [DC Brake Time] and P394 [DC Brake
Level]. This mode of braking generates up to 40% of rated motor torque for
braking and is typically used for low inertia loads with infrequent Stop cycles:
• On Stop, 3 phase drive output goes to zero (off ).
• Drive outputs DC voltage on the last used phase to provide the current
level programmed in P394 [DC Brake Level]. This voltage causes a
stopping brake torque. If the voltage is applied for a time that is longer
than the actual possible stopping time, the remaining time is used to
attempt to hold the motor at zero speed (decel profile “B” on the diagram
above).
• DC voltage to the motor continues for the amount of time programmed in
P395 [DC BrakeTime]. Braking ceases after this time expires.
• After the DC Braking ceases, no further power is supplied to the motor.
The motor/load may or may not be stopped. The drive has released
control of the motor/load (decel profile “A” on the diagram above).
• The motor, if rotating, coasts from its present speed for a time that is
dependent on the remaining kinetic energy and the mechanics of the
system (inertia, friction, and so forth).
• Excess motor current and/or applied duration, could cause motor damage.
Motor voltage can exist long after the Stop command is issued. The right
combination of Brake Level and Brake Time must be determined to
provide the safest, most efficient stop (decel profile “C” on the diagram
above).
Bus Voltage
Output Voltage
Output Current
Motor Speed
Command Speed
Time
DC Hold Time
Stop Command
(B) (C) (A)