Flux Up 2-97
Flux Up [Flux Up Mode]
AC induction motors require flux to be established before controlled torque
can be developed. To build flux in these motors, voltage is applied to them.
PowerFlex drives have two methods to flux the motor.
The first method is a normal start. During a normal start, flux is established
as the output voltage and frequency are applied to the motor. While the flux
is being built, the unpredictable nature of the developed torque may cause
the rotor to oscillate even though acceleration of the load may occur. In the
motor, the acceleration profile may not follow the commanded acceleration
profile due to the lack of developed torque.
Figure 2.21 Accel Profile during Normal Start - No Flux Up
The second method is Flux Up Mode. In this mode, DC current is applied to
the motor at a level equal to the lesser of the current limit setting, drive rated
current, and drive DC current rating. 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.
Figure 2.22 Flux Up Current versus Flux Up Time
[Flux Up Time]
Once rated flux is reached in the motor, normal operation begins and the
desired acceleration profile is achieved.
Time
0
Frequency
Reference
Frequency
Rated Flux
Rotor
Stator
Oscillation due
to flux being
established
Flux Up Time
Flux Up Current = Maximum DC Current
Rated Motor Flux
Motor Flux
Rated Flux
Current
T1
T2
T3
T4
Flux Up Current
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