National Instruments Xmath Interactive Control Design Module ICDM Instrukcja Użytkownika Pobierz pdf (Strona 46)

Chapter 4 PID Synthesis

Xmath Interactive Control Design Module 4-6 ni.com

Derivative Term Normalization

The derivative term is low-frequency normalized, which means that at low

frequencies (below 1/T

diff

) 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 T

diff

term small and then

gradually increasing it until you get a good balance between better stability

margins and excessive actuator effort.

Rolloff Term Normalization

The two HF rolloff terms are low-frequency normalized, so they have little

effect at frequencies below T

. You can start with small values for these

parameters, and then gradually increase them until you start to notice a

degradation in stability.

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National Instruments Xmath Interactive Control Design Module ICDM Instrukcja Użytkownika Strona 46