Process Pi For Standard Control - Allen-Bradley PowerFlex 70 User Manual
Adjustable frequency ac drives
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Process PI for Standard
Control
The internal PI function of the PowerFlex 70 provides closed loop process
control with proportional and integral control action. The function is designed
for use in applications that require simple control of a process without external
control devices. The PI function enables the microprocessor of the drive to
follow a single process control loop.
The PI function reads a process variable input to the drive and compares it to a
desired setpoint stored in the drive. The algorithm then adjusts the output of the
PI regulator, changing drive output frequency to try and make the process
variable equal the setpoint.
It can operate as trim mode by summing the PI loop output with a master speed
reference.
Slip Adder
Spd Ref
PI Ref
Process PI
Controller
PI Fbk
PI Enabled
Or, it can operate as control mode by supplying the entire speed reference. This
method is identified as Exclusive mode.
Slip Adder
Spd Ref
PI Ref
Process PI
Controller
PI Fbk
PI Enabled
PI Enable
The output of the PI loop can be turned on (enabled) or turned off (disabled).
This control enables the user to determine when the PI loop is providing part or
all of the commanded speed. The logic for enabling the PI loop is shown in
below.
Drive
Drive
Ramping
Drive
Running
to Stop
Jogging
A Digital Input
is Configured
to PI Enable
The drive must be running for the PI loop to be enabled. The loop is disabled
when the drive is ramping to a stop, jogging, or the signal loss protection for the
analog input or inputs is sensing a loss of signal.
Rockwell Automation Publication 20A-UM001N-EN-P - July 2013
Slip
Comp
+
+
Open
Loop
Linear Ramp
Spd Cmd
& S-Curve
Process
+
PI
+
Speed Control
Slip
Comp
+
+
Open
Loop
Linear Ramp
Spd Cmd
& S-Curve
Process
PI
Speed Control
Bit 0 of
The PI Loop
[PI Control] = 1
is Enabled
(enabled)
Signal Loss
"Enabled" Status
Digital Input
is Reflected
in [PI Status]
The Configured
Bit 0 = 1
Digital Input
is Closed
Application Notes
Appendix C
119
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