Allen-Bradley PowerFlex 70 Reference Manual page 141

• Feedback Square Root - This feature uses the square root of the feedback
signal as the PI feedback. This is useful in processes that control pressure,
since centrifugal fans and pumps vary pressure with the square of speed.
The PI has the option to take the square root of the selected feedback
signal. This is used to linearize the feedback when the transducer produces
the process variable squared. The result of the square root is normalized
back to full scale to provide a consistent range of operation. The option to
take the square root is selected in the PI Configuration parameter.
100.0
75.0
50.0
25.0
0.0
-25.0
-50.0
-75.0
-100.0
-100.0 -75.0
• Stop Mode (PowerFlex 700 Only). When Stop Mode is set to "1" and a
Stop command is issued to the drive, the PI loop will continue to operate
during the decel ramp until the PI output becomes more than the master
reference. When set to "0, " the drive will disable PI and perform a normal
stop. This bit is active in Trim mode only.
• Anti-Wind Up (PowerFlex 700 Only). When Anti-Windup is set to "1"
the PI loop will automatically prevent the integrator from creating an
excessive error that could cause loop instability. The integrator will be
automatically controlled without the need for PI Reset or PI Hold inputs.
•
Torque Trim. When Torque Trim is set to "1" the output of
Vector FV
the process PI loop will be added to Torque Reference A and B, instead of
being added to the speed reference.
2. [PI Control] is a set of bits to dynamically enable and disable the operation of
the process PI controller. When this parameter is interactively written to from
a network it must be done through a data link so the values are not written to
EEprom.
• PI Enable - The PI loop can be enabled/disabled. The Enabled status of
the PI loop determines when the PI regulator output is part or all of the
commanded speed. The logic evaluated for the PI Enabled status is shown
in the following ladder diagram.
The drive must be in run before the PI Enabled status can turn on. The PI
will remain disabled when the drive is jogged. The PI is disabled when the
drive begins a ramp to stop, except in the PowerFlex 700 when it is in Trim
mode and the Stop mode bit in [PI Configuration] is on.
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
-50.0 -25.0 0.0 25.0
Normalized Feedback
Process PI Loop
50.0 75.0 100.0
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