Allen-Bradley PowerFlex 70 Reference Manual page 136

Process PI Loop
136
The PI function can perform a combination of proportional and integral control.
It does not perform derivative control, however, the accel / decel control of the
drive can be considered as providing derivative control.
There are two ways the PI Controller can be configured to modify the
commanded speed.
• Process Trim - The PI Output can be added to the master speed reference
• Process Control - PI can have exclusive control of the commanded speed.
The selection between these two modes of operation is done in the [PI
Configuration] parameter.
Process Trim
Process Trim takes the output of PI regulator and sums it with a master speed
reference to control the process. In the following example, the master speed
reference sets the wind/unwind speed and the dancer pot signal is used as a PI
Feedback to control the tension in the system. An equilibrium point is
programmed as PI Reference, and as the tension increases or decreases during
winding, the master speed is trimmed to compensate and maintain tension near
the equilibrium point.
Equilibrium Point
[PI Reference Sel]
When the PI is disabled the commanded speed is the ramped speed reference.
Slip Adder
Spd Ref
PI Ref
Process PI
Controller
PI Fbk
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
0 Volts
Dancer Pot
[PI Feedback Sel]
10 Volts
Master Speed Reference
+
+
Linear Ramp
& S-Curve
+
+
PI Disabled
Slip
Comp
Open
Loop
Spd Cmd
Process
PI
Speed Control