Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 218)

218 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 4 Motor Control
Flux Regulator The flux regulator is used to control and limit the overall (fundamental) voltage
applied to an induction motor when FOC is used. The flux regulator controls
field weakening above base speed and maintains voltage margin for a current
regulator. A variation of the induction motor flux regulator is used for PM
motors for operation above base speed.
As default the flux regulator is enabled. When disabled, the current regulator
becomes de-tuned.
Do not disable this regulator. If you feel you need to disable this function, consult
the factory for verification.
Flux Up AC induction motors require flux to be established before controlled torque can
be developed. To build flux, voltage is applied. There are two methods to flux the
motor.
The first method is Automatic during a normal start. Flux is established as the
output voltage and frequency are applied to the motor. While the flux is being
established, the unpredictable nature of the developed torque can cause the rotor
to oscillate even though acceleration of the load can occur. In the motor, the
acceleration profile may not follow the commanded acceleration profile due to
the lack of developed torque.
Figure 23 - Accel Profile during Normal Start - No Flux Up
The second method is Manual. In this mode, DC current is applied to the motor
so that the flux is established before rotation. The flux up time period is based on
the level of flux up current and the rotor time constant of the motor. The flux up
current is not user adjustable.
0
Stator
Rotor
Frequency
Reference
Rated Flux
Oscillation due to flux
being established.
Time
Fre
qu
en
cy