Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 54)

54 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 1 Drive Configuration
Feedback Devices There are three different feedback option modules available for PowerFlex 750-
Series AC Drives:
• Single Incremental Encoder (20-750-ENC-1)
• Dual Incremental Encoder (20-750-DENC-1)
• Universal Feedback (20-750-UFB-1)
The Dual Incremental Encoder and Universal Feedback modules each support
up to two encoders while the Single Incremental Encoder supports one encoder.
Multiple feedback option modules can be installed in the drive, however there is a
limit of two feedback modules if using Integrated Motion on EtherNet/IP.
For more information on the option modules, including specifications and wiring
information, see the PowerFlex 750-Series AC Drives Installation Instructions,
publication
750-IN001 .
For more information on encoder feedback options, including connections and
compatibility, see Appendix E of the PowerFlex 750-Series Programming
Manual, publication
750-PM001 .
Flying Start The Flying Start feature is used to start into a rotating motor, as quick as possible,
and resume normal operation with a minimal impact on load or speed.
When a drive is started in its normal mode it initially applies a frequency of 0 Hz
and ramps to the desired frequency. If the drive is started in this mode with the
motor already spinning, large currents are generated. An over current trip can
result if the current limiter cannot react quickly enough. The likelihood of an
over current trip is further increased if there is a residual flux (back emf ) on the
spinning motor when the drive starts. Even if the current limiter is fast enough to
prevent an over current trip, it can take an unacceptable amount of time for
synchronization to occur and for the motor to reach its desired frequency. In
addition, larger mechanical stress is placed on the application.
In Flying Start mode, the drive’s response to a start command is to synchronize
with the motors speed (frequency and phase) and voltage. The motor then
accelerates to the commanded frequency. This process prevents an over current
trip and significantly reduce the time for the motor to reach its commanded
frequency. Because the drive synchronizes with the motor at its rotating speed
and ramps to the proper speed, little or no mechanical stress is present.
The Sweep function is currently not in the PowerFlex 750-Series drives frame 8
and larger.