Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 80)

80 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 1 Drive Configuration
sooner, however if the step is too large the drive can go into current limit and
extend the acceleration.
Preload command can be used when the PID has exclusive control of the
commanded speed. With the integrator preset to the commanded speed there is
no disturbance in commanded speed when PID is enabled. After PID is enabled
the PID output is regulated to the required level.
When the PID is configured to have exclusive control of the commanded speed
and the drive is in current limit or voltage limit the integrator is preset to the
commanded speed so that it knows where to resume when no longer in limit.
Ramp Ref
The PID Ramp Reference feature is used to provide a smooth transition when
the PID is enabled and the PID output is used as a speed trim (not exclusive
control). When PID Ramp Reference is selected in the PID Configuration
parameter, and PID is disabled, the value used for the PID reference is the PID
feedback. This causes the PID error to be zero. Then when the PID is enabled the
value used for the PID reference ramps to the selected value for PID reference at
the selected acceleration or deceleration rate. After the PID reference reaches the
selected value the ramp is bypassed until the PID is disabled and enabled again. S-
curve is not available as part of the PID linear ramp.
Diagram A Diagram B
PID Enabled
PID Output
Speed Command
PID Preload Value = 0 PID Preload Value > 0
PID Preload Value
PID Enabled
PID Output
Speed Command
Preload to Command Speed
Start at Speed Command