I was simulating 3 types of speed controller types for flying shears. P, PI and PD speed controller. And my question again is, what is the reason for not using PD control even if it can theoretically be the best option.
While P- and I-parts of controllers are relatively "unidirectional" to tune, the D-part is not. Without a reliable model for your plant, a D-part in the controller is likely to do more harm than good. Do you have a reliable transfer function of your "plant"? Or in other words, what do you mean by "theoretically the best option"?
P controller provide rapid initial response to drive system. I controller provide to system outputs to go reference input, without I controller system output can not equal reference input, D controller provide to maintain system reference value against sharp disturbance. Without I controller your system may not go reference input.
Norman Urs Baier as i said my application is rotary flying shears in material processing lines. And i was doing comparsion of speed drop during cut with use of P, PI and PD speed control. Simulations were done in matlab and when i looked into for example Siemens manuals for rotary shears, they are using PI speed control not PD so i was curious why