Finding Transfer Function from Step Response
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Max Mai Tobon
on 23 Oct 2020
Commented: Ameer Hamza
on 30 Oct 2020
A bit of context:
I'm in a stundent project at my universtiy. We're desingning and building an Mechanical ventilator for Corona-Patients. I'm having some trouble with the control loop of the system.
The ouput of the control loop is controlling a proportional valve. The purpose of this is to reach the desired pressure (Setpoint) in less than 3 seconds. I'm using a PID control, yet it's not tuned correctly. That's why I decided to go to basics, and get the transfer function from a step response, to then simulate the different constants in MATLAB.
The following step response was achieved by opening the proportional valve fully, and waited till the Setpoint was achieved. There's a 1 bar relative pressure in the system. Any pressure above 25mbar flows out, through a PEEP valve. The proplem with the system is that we can't overshot, because we cannot get rid of this pressure as the patient is inhaling.
If someone could help me, calculate the transfer function of the following step response, I would be really gratefull.
Thanks in advance.
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Accepted Answer
Ameer Hamza
on 23 Oct 2020
Edited: Ameer Hamza
on 23 Oct 2020
You can do it using the system identification app: https://www.mathworks.com/help/ident/ref/systemidentification-app.html. For this, you also need the toolbox: https://www.mathworks.com/help/ident/index.html
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Ameer Hamza
on 23 Oct 2020
I am glad to be of help! You can find many examples in the documentation.
More Answers (1)
Ameer Hamza
on 23 Oct 2020
Edited: Ameer Hamza
on 23 Oct 2020
Another approach can be something like this. Consider the transfer function of the system is
and the transfer function of input step function is
The transfer function of output will be
which in time-domain become
Here you have y(t). You can use fmincon() to estimate a and b.
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