Rockwell Automation 20B PowerFlex 70, PowerFlex 700 Reference Manual - Manual (Page 99)

Drive Ratings (kW, Amps, Volts)
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013 99
torque load reducing the output frequency does not lower the current (load).
Lowering current limit on a CT load will push the drive down to a region where
the thermal issue becomes worse. In this situation the thermal manager will
increase the calculated losses in the power module to track the worst case IGBT.
For example, if the thermal manager normally provides 150% for 3 seconds at
high speeds, it may only provide 150% for one second before generating a fault at
low speeds.
If operating at 60Hz 120%, lowering the current limit may cause a fault sooner
than allowing the drive to continue to operate. In this case the user may want to
disable current limit fold back.
Drive Ratings (kW, Amps,
Volts)
Refer to Fuses and Circuit Breakers on page 106 .
Droop
Droop is used to “shed” load and is usually used when a soft coupling
of two motors is present in an application. The master drive speed regulates and
the follower uses droop so it does not “fight” the master. The input to the droop
block is the commanded motor torque. The output of the droop block reduces
the speed reference. [Droop RPM @ FLA] sets the amount of speed, in RPM,
that the speed reference is reduced when at full load torque. For example, when
[Droop RPM @ FLA] is set to 50 RPM and the drive is running at 100% rated
motor torque, the droop block would subtract 50 RPM from the speed reference.
Economizer
(Auto-Economizer)
Refer to Torque Performance Modes on page 201 .
Economizer mode consists of the sensorless vector control with an additional
energy savings function.
When steady state speed is achieved, the economizer becomes active and
automatically adjusts the drive output voltage based on applied load. By matching
output voltage to applied load, the motor efficiency is optimized. Reduced load
commands a reduction in motor flux current. The flux current is reduced as long
as the total drive output current does not exceed 75% of motor rated current as
programmed in [Motor NP FLA], parameter 42. The flux current is not allowed
to be less than 50% of the motor flux current as programmed in [Flux Current
Ref ], parameter 63. During acceleration and deceleration, the economizer is
inactive and sensorless vector motor control performs normally.
Vector
Maximum Voltage
Maximum
Frequency Frequency
V
total
Motor Nameplate Voltage
Motor Nameplate
Frequency
Ir Voltage
0
0
Rated Flux Current
Reduced Flux Current,
minimum of 50% of Rated Flux Current
Increasing
Load