Rockwell Automation 21G PowerFlex 750-Series AC Drives Reference Manual - Manual (Page 22)

22 Rockwell Automation Publication 750-RM001F-EN-P - February 2012
Chapter 1 Safety Concept
Understanding Commutation
Permanent magnet (PM), brushless AC motors are a class of synchronous motor
that depends on electronic brushless commutation for their operation. In PM
brushless motors, an electromagnetic field is created by the permanent magnets
on the rotor. A rotating magnetic field is created by a number of electromagnets
commutated electronically with IGBT’s at the right speed, order, and times.
Movement of the electromagnetic field is achieved by switching the currents in
the coils of the stator winding. This process is called commutation. Interaction of
the two electromagnetic fields produces magnetic force or torque.
For example, with the PowerFlex 755 drive, follow these guidelines to make sure
that the incremental encoder or high-resolution feedback device is used for
commutation:
• Set P35 [Motor Cntl Mode] = 1 “Induction FV” or 6 “PM FV”
• Set P125 [Pri Vel Fdbk Sel] = any available feedback device
• Set P635 [Spd Options Ctrl] bit 7 “Auto Tach SW” = 0
Contact Information if Safety
Option Failure Occurs If you experience a failure with any safety-certified device, contact your local
Rockwell Automation distributor. With this contact, you can:
• return the device to Rockwell Automation so the failure is appropriately
logged for the catalog number affected and a record is made of the failure.
• request a failure analysis (if necessary) to determine the probable cause of
the failure.