Chapter 4 PID Synthesis
Xmath Interactive Control Design Module 4-6 ni.com
Derivative Term NormalizationThe derivative term is low-frequency normalized, which means that at low
frequencies (below 1/Tdiff) it is nearly one, and so has little effect on the
overall controller transfer function at low frequencies. In particular, the
loop transfer function at s= 0 is not affected by the derivative term at all,
so static tracking, static actuator effort, and so on are not affected by the
derivative term. You can start by making the Tdiff term small and then
gradually increasing it until you get a good balance between better stability
margins and excessive actuator effort.
Rolloff Term NormalizationThe two HF rolloff terms are low-frequency normalized, so they have little
effect at frequencies below Thf. You can start with small values for these
parameters, and then gradually increase them until you start to notice a
degradation in stability.