Why does this step response overshoot?

[215]

I have this transfer function which i don't know why it is overshooting due to an step input.

http://snag.gy/Vh1SM.jpg

Could someone explain why it does that.

It's it a close loop transfer function, where I've designed a controller for it, but for some reason, eventhoug all my poles are placed correctly, it is not possible to get the response i want to.

 

[rude man]

With the given transfer function there is no overshoot.
Wolfram alpha agrees!

 

[215]

but ... http://snag.gy/0eODb.jpg
how come??

 

[rude man]

Oops, there is too a small overshoot. I couldn't see it on wolfram. It's due to the zero at s = -1.513. Sorry!
You can cancel it by inserting a pole at the same point (s = - 1.513).

 

[215]

But how come does zeroes apply overshoot? I thought it was only poles which affected the system

 

[milesyoung]

With the given transfer function there is no overshoot.
Wolfram alpha agrees!

You should check your entry. It does have overshoot.

I have this transfer function which i don't know why it is overshooting due to an step input.

http://snag.gy/Vh1SM.jpg

Could someone explain why it does that.

The transient response of your system is not only determined by its poles. You have a LHP zero as well, which can have a significant impact on the overshoot of the step response of your system.

Quick Google search for 'poles zeros transient' turned up:
http://courses.engr.illinois.edu/ece486/documents/lecture_notes/effects_zero_pole.pdf

 

[215]

but what criteria should i apply for determining the zeroes, and how does it affect the system. I mean it is still a LHP zero? so bad can't it be

 

[215]

How should i using a PID controlle be able to adjust the Zero location, while i am adjusting the location of the pole.

 

[rude man]

You need to describe your problem more fully, not just talk about an isolated transfer function. What is your plant and what are the response criteria?

 

[215]

I tried to make a general problem, but seems to have forgotten where it began at.
I posted my problem on another forum.

http://snag.gy/OqhxH.jpg

I hope this helps.
My repsponse criterias is that I want an overshoot to be 0% and settling time be under 1 sec.
Using Matlab tuning application i managed to do with only the I part of the controller. The problem is though I've read a lot of places that it is not recomended to use just I or D regulators.