Rockwell Automation 1336T FORCE Series B - Manual (Page 227)

Chapter 6
Troubleshooting
6–15
Forcing the Drive to Complete a Precharge
In some cases, the precharge may not complete due to external bus
disturbances. Setting bit 11 in Bus/Brake Opts forces the precharge to
complete at the precharge interval (default 30 seconds). This may cause
precharge damage and should only be used when large inrush currents
cannot occur.
Precharge/Ridethrough Selection (parameter 223) also lets you select a
rate, called a slew rate, for the bus voltage tracker. The bus voltage
tracker slowly tracks changes in the actual bus voltage. If the actual bus
voltage drops 150 volts or greater below the current value of the bus
voltage tracker, the drive automatically disables modulation and enters
precharge.
Important: You should only use the bus voltage tracker if you are
having ridethrough problems. The bus voltage tracker
adjusts the bus sensitivity to ridethrough for cases where
there is an unstable bus.
By changing the rate used for the bus voltage tracker, you can make your
system more or less sensitive to changes in the actual bus voltage. For
example, if your drive currently enters precharge after the motor exits
regeneration, you may need to change your slew rate.
Figure 6.4 shows an example of the filtered bus voltage reference.
Figure 6.4
Example Bus Voltage Line
Volts
Time
150V
Bus voltage tracker
A
B
C
Actual bus voltage
At point A, the motor was in regeneration, so the value of the bus voltage
tracker slowly increased.
Understanding the Bus
Voltage Tracker