PID Tuning tells me the system has closed loop stability even though it doesn't

Hello everyone,

I am using the PID Tuning App to design a PID controler for my plant. It works pretty good, the systems reaction is pretty solid and the PID Tuning tells me that I have closed loop stability.

The problem is, when I check the root locus, it has some poles with positive real values, indicating my system is unstable. There is even a branch that is not reaching into the negative pane, so it would seem impossible to stabilize the system.

Also, if I design the controler with the "sisotool", I get the same result.

Is there something I might be missing?

Thank you in advance for any help!

Is it sometimes acceptable to work with a system even though it is not stable?

Answer 1

[Arkadiy Turevskiy]

Could it be the same issue as in this question ?

If not, then please attach your models/files- hard to troubleshoot otherwise.