Estimation of Transfer Function of a Setup

Dear Experts,

I have an setup with 2416 eurotherm pid controller with thermocouple in feedback, attached to a system. After putting the pid to auto tune mode, am getting the closed loop output graph.

How can i estimate the transfer function of the system.

The Setpoint of PID is known, PID parameters are known, Output response is known. How can i determine the transfer function of the system.

Thanks Nitish

Answer 1

[Arkadiy Turevskiy]

You can use System Identification Toolbox to estimate closed-loop transfer function T from setpoint to output. That transfer function is T=GC/(1+GC), where G is plant transfer function and C is controller transfer function.

So if you know T (estimated with System Identification Toolbox) and C (your PID controller), you can calculate G as G=T/(C-TC).

For estimating T, you can use a new algorithm ssarx that we added in R2013b which works well for estimation from closed-loop data. Details are in the release notes.

HTH.

Arkadiy