GPS-X Technical Reference

353 Tools Object
When both the process and disturbance dynamics are represented by first-order plus dead time
models, perfect feedforward control can in principle be achieved if one:
Sets the feedforward gain K FF to the disturbance-to-process gain ratio;
The dead time to the difference between disturbance and process dead times (possible
only when the process dead time is less than the disturbance dead time);
ld the lead time to the process time constant; and,
The lag time lg to the disturbance time constant.
Implementation in GPS-X
The feedback control action is calculated from a PID control algorithm as described
above, and the feedforward control action is added to it as follows:
Feedforward/Feedback (PID in velocity form):
Equation 12.24
Feedforward/Feedback (PID in position form):
Equation 12.25
where:
ΔMV N
FF
= the change in feedforward control action obtained from discretizing the
lead/lag algorithm and the superscript FF refers to the feedback
controller.
GPS-X Technical Reference