Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 84)

84 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 1 Drive Configuration
PI Reset
This feature holds the output of the integral function at zero. The term “anti
windup” is often applied to similar features. It can be used for integrator
preloading during transfer and can be used to hold the integrator at zero during
“manual mode.”
For example a process whose feedback signal is below the reference point,
creating error. The drive increases its output frequency in an attempt to bring the
process into control. If, however, the increase in drive output does not zero the
error, additional increases in output is commanded. When the drive reaches
programmed Maximum Frequency, it is possible that a significant amount of
integral value has been “built up” (windup). This can cause undesirable and
sudden operation if the system were switched to manual operation and back.
Resetting the integrator eliminates this windup.
Invert Error
This feature changes the “sign” of the error, creating a decrease in output for
increasing error and an increase in output for decreasing error. An example of this
is an HVAC system with thermostat control. In Summer, a rising thermostat
reading commands an increase in drive output because cold air is being blown. In
Winter, a falling thermostat commands an increase in drive output because warm
air is being blown. The PID has the option to change the sign of PID Error. This
is used when an increase in feedback needs to cause an increase in output. The
option to invert the sign of PID Error is selected in the PID Configuration
parameter.