Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 47)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 47
Drive Configuration Chapter 1
Internal Resistor
If the drive is set up for an internal resistor, there is a protection scheme built into
the firmware such that if it is determined that too much power has been
dissipated into the resistor the firmware does not allow the DB transistor to fire
any longer. Thus the bus voltage rises and trips on over voltage.
Figure 4 - PowerFlex 750-Series Bus Regulation – Internal Dynamic Brake Resistor
External Resistor
If the drive is set up for an external resistor and the resistor has been sized
correctly and the regenerative power limit is set to a value that enables the
regenerative power to be fully dissipated, the DB transistor continues to fire
throughout the decel time.
Figure 5 - PowerFlex 750-Series Bus Regulation – External Dynamic Brake Resistor
900
800
700
600
500
400
300
200
100
0
12
10
8
6
4
2
0
-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
DC Bus Voltage DC Current
DC Bus
Seconds
DC B
us
V
olt
s
10
Vol
ts = Base
Speed
Speed Fdbk
Over Voltage Trip
Motor Speed
Brake Current
800
780
760
740
720
700
680
660
14
12
10
8
6
4
2
0
-2
-0.2 0 0.2 0.4 0.6 0.8 1 1.2
DC Bus Voltage DC Current
DC Bus
Seconds
DC B
us
V
olt
s
10
V
olt
s =
B
ase
Sp
ee
d
Speed Fdbk
Motor Speed
Brake Current