Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017 9
Understanding How Dynamic Braking Works Chapter 1
Chopper Transistor Voltage Control regulates the voltage of the DC bus during
regeneration. The average values of DC bus voltages are:
Voltage dividers reduce the DC bus voltage to a value that is usable in signal
circuit isolation and control. The DC bus feedback voltage from the voltage
dividers is compared to a reference voltage to actuate the Chopper Transistor.
The Freewheel Diode (FWD), in parallel with the Dynamic Brake Resistor,
allows any magnetic energy stored in the parasitic inductance of that circuit to be
safely dissipated during turn off of the Chopper Transistor.
Resistor
The Resistor dissipates the regenerated energy in the form of heat. The
PowerFlex Family of Drives can use either the internal dynamic brake resistor
option or an externally mounted dynamic brake resistor wired to the drive.
Wiring
Frames 0…4
Wire to the DB resistor should be no longer than 10 feet from the drive
terminals. Wire should be twisted to minimize inductance.
Frames 5…6
Wire to the DB resistor should be no longer than 100 feet from the drive
terminals.
Drive Input Voltage Transistor Turn-On
Voltage
Maximum Power Calculation
Voltage
208 375V DC 395V DC
240 375V DC 395V DC
400 750V DC 790V DC
480 750V DC 790V DC
575 937.5V DC 987V DC
600 937.5V DC 987V DC
600 (Frame 5 and 6) 1076V DC 1135V DC
690 1076V DC 1135V DC
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