Allen-Bradley PowerFlex 70 Reference Manual page 137

When the PI is enabled, the output of the PI Controller is added to the ramped
speed reference.
Slip Adder
Spd Ref
PI Ref
Process PI
Controller
PI Fbk
Exclusive Control
Process Control takes the output of PI regulator as the speed command. No
master speed reference exists and the PI Output directly controls the drive
output.
In the pumping application example below, the reference or setpoint is the
required pressure in the system. The input from the transducer is the PI feedback
and changes as the pressure changes. The drive output frequency is then increased
or decreased as needed to maintain system pressure regardless of flow changes.
With the drive turning the pump at the required speed, the pressure is
maintained in the system.
Motor
PI Feedback
However, when additional valves in the system are opened and the pressure in the
system drops, the PI error will alter its output frequency to bring the process back
into control.
When the PI is disabled the commanded speed is the ramped speed reference.
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
+
+
Linear Ramp
& S-Curve
+
+
PI Enabled
Pump
Desired Pressure
[PI Reference Sel]
Process PI Loop
Slip
Comp
Open
Loop
Spd Cmd
Process
PI
Speed Control
Pressure
Transducer
137