Allen-Bradley PowerFlex 70 Reference Manual page 140

Process PI Loop
140
PI Enabled
PI Output
Spd Cmd
• Ramp Ref - The PI Ramp Reference feature is used to provide a smooth
transition when the PI is enabled and the PI output is used as a speed trim
(not exclusive control),.
When PI Ramp Reference is selected in the PI Configuration parameter,
and PI is disabled, the value used for the PI reference will be the PI
feedback. This will cause PI error to be zero. Then when the PI is enabled
the value used for the PI reference will ramp to the selected value for PI
reference at the selected acceleration or deceleration rate. After the PI
reference reaches the selected value the ramp is bypassed until the PI is
disabled and enabled again. S-curve is not available as part of the PI linear
ramp.
• Zero Clamp - This feature limits the possible drive action to one direction
only. Output from the drive will be from zero to maximum frequency
forward or zero to maximum frequency reverse. This removes the chance
of doing a "plugging" type operation as an attempt to bring the error to
zero.
The PI has the option to limit operation so that the output frequency will
always have the same sign as the master speed reference. The zero clamp
option is selected in the PI Configuration parameter. Zero clamp is
disabled when PI has exclusive control of speed command.
For example, if master speed reference is +10 Hz and the output of the PI
results in a speed adder of –15 Hz, zero clamp would limit the output
frequency to not become less than zero. Likewise, if master speed reference
is –10 Hz and the output of the PI results in a speed adder of +15 Hz, zero
clamp would limit the output frequency to not become greater than zero.
Linear
Spd Ref
Ramp
& S-Curve
PI Ref
Process PI
Controller
PI Fbk
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
Start at Spd Cmd
Pre-load to Command Speed
≥ 0
PI_Config
.ZeroClamp
+
Spd Ramp
+
PI Output
+32K
0
0
Spd Cmd
-32K
+32K
-32K