(Control) Derivative filter and discrete model

  • #1
Leo Liu
353
156
Hi I am back :).

I have been doing some Simulink modeling for a project. I modeled it with a discrete system due to the controller rate. I have noticed that for all the discrete system I have tried, adding a derivative filter not only improves the performance (smaller settling time), but it is sometimes also necessary.

The following example involving a discrete PID and a 2nd order discrete transfer function illustrates the behaviour:
1700043797637.png

Autotune with no derivative filter N:
1700043894118.png

Autotune with derivative filter N:
1700044075414.png


I was wondering why such a behaviour would occur. Also, should I model the transfer function as discrete or continuous system for a physical system like F=ma? Any input will be appreciated.
 

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