Rockwell Automation 20G PowerFlex 750-Series AC Drives User Manual
Page 203
Rockwell Automation Publication 750-RM002B-EN-P - September 2013
203
Motor Control
Chapter 4
negative when deceleration starts. (this point called -Pb is the first value that
needs to be calculated). The cycle is then repeated.
Dynamic Braking Module (no longer a Rockwell Automation product)
shows a simplified schematic of a Chopper Module with Dynamic
Brake Resistor. The Chopper Module is shown connected to the positive and
negative DC bus conductors of an AC PWM Drive. The two series connected
Bus Caps are part of the DC bus filter of the AC Drive. The significant power
components of the Chopper Module are the protective fusing, the Crowbar
SCR, the Chopper Transistor (an IGBT), the Chopper Transistor Voltage
Control (hysteretic voltage comparator), and a freewheel diode for the Dynamic
Brake Resistor.
The protective fuse is sized to work in conjunction with the Crowbar SCR.
Sensing circuitry within the Chopper Transistor Voltage Control determines if
abnormal conditions exist within the Chopper Module. One of these abnormal
conditions is a shorted Chopper Transistor. If this condition is sensed, the
Chopper Transistor Voltage Control fires the Crowbar SCR, shorting the DC
0
t1
t2 t3
t4
t1 + t4
t
0
t1
t2 t3
t4
t1 + t4
t
0
t1
t2 t3
t4
t1 + t4
t
ω(t)
T(t)
P(t)
-Pb