Rockwell Automation Publication 22C-UM001J-EN-E - January 2017
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Application Notes
Appendix D
Figure 40 - Good Response – Critically Damped
Auxiliary Motor Control
Setup
The PowerFlex 400 has a built in Auxiliary Motor Control feature. This
feature allows operation of up to three (3) line-started motors in addition to
the motor controlled directly by the PowerFlex 400 drive. System output can
vary from 0% (auxiliary motors off and drive-controlled motor at zero speed)
to 400% (3 auxiliary motors and drive-controlled motor at full speed). To
enable the Auxiliary Motor Control, parameter
[Aux Motor Mode]
must be set to an option 1 “Enabled.” When enabled, the internal PID
controller in the PowerFlex 400 uses a reference and feedback signal to adjust
the speed of the drive controlled motor such that the feedback signal follows
the reference signal. When demand exceeds the first motors capacity, the
PowerFlex 400 Auxiliary Motor Control automatically starts an auxiliary
motor. The speed of the drive controlled motor is reduced to account for the
auxiliary motors additional output to the system. If demand continues to
increase, the PowerFlex Auxiliary Motor Control starts additional motors
using the same process. When demand decreases, an auxiliary motor is stopped
and the PowerFlex Auxiliary Motor Control increases the speed of the drive
controlled motor to account for lost system output. A Motor Interlock input
identifies motors that are out of service and causes them to skipped over to the
next available motor.
An AutoSwap function also can be used which allows equal wear to be placed
on each motor by periodically swapping the drive controlled and auxiliary
motors. Each motor in the system will over time be connected to the PowerFlex
400 drive and also directly to the AC line. During an AutoSwap, the motor
directly connected to the PowerFlex 400 drive is stopped and the contactor is
opened. The contactor of the next motor that will be controlled by the
PowerFlex 400 drive is opened if running across the AC line. A contactor is
closed connecting this motor directly to the PowerFlex 400 drive and is started.
An additional motor is line started if required.
PID Feedback
PID Reference
Time
