Allen-Bradley PowerFlex 70 Reference Manual page 139

Process PI Loop
PI_Config
.Invert
+
PI Ref Sel PI Error
–
PI_Config
.Sqrt -
PI Fdbk Sel PI Fbk
• Preload Integrator - This feature allows the PI Output to be stepped to a
preload value for better dynamic response when the PI Output is enabled.
Refer to diagram 2 below.
If PI is not enabled the PI Integrator may be initialized to the PI Pre-load
Value or the current value of the commanded speed. The operation of
Preload is selected in the PI Configuration parameter.
PI_Config PI_Status
.PreloadCmd .Enabled
Preload Value PI Integrator
Spd Cmd
By default, Pre-load Command is off and the PI Load Value is zero, causing
a zero to be loaded into the integrator when the PI is disabled. As below
shown on the left, when the PI is enabled the PI output will start from zero
and regulate to the required level. When PI is enabled with PI Load Value
is set to a non-zero value the output begins with a step as shown below on
the right. This may result in the PI reaching steady state sooner, however if
the step is too large the drive may go into current limit which will extend
the acceleration.
PI Enabled
PI Pre-load Value
PI Output
Spd Cmd
PI Pre-load Value = 0 PI Pre-load Value > 0
Pre-load command may be used when the PI has exclusive control of the
commanded speed. With the integrator preset to the commanded speed
there is no disturbance in commanded speed when PI is enabled. After PI
is enabled the PI output is regulated to the required level.
When the PI 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.
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013 139