## understanding the system modeling

## understanding the system modeling

(OP)

Hello,

This is sundaram, I'm working on a speed control of belt driven drum project and I'm new to control system concepts.

I'm trying to find the transfer function of the system so that I can model it in simulink and tune the PID and look in to other aspects of the system.

The blocks and variable i'm outputting is in the attached Image (picture 2)

http://files.engineering.com/getfile.aspx?folder=a...

The speed loop control (PID) is in the control block and it has a microcontroller in it (where I tuned the system partially).

Now the variable I'm out putting on to the scope is the internal speed var which gets calculated at a rate of 18KHz .

From the over shoots and rise time I could calculate damping ratio and natural frequency in rad/sec

and substitute in the standard 2nd order system transfer function.

But the 2nd order transfer function which I got above includes the PID control which is in the microcontroller.

But to the best of my knowledge it should not be included and it should be separated,then only I can use it in MATLAB.

From the diagram (picture 3) H(s) is the transfer function I have, D(s) is the PID loop and G(s) is the plant model.

http://files.engineering.com/getfile.aspx?folder=7...

Can anyone help me, I'm I right in my approach ?, if so how can I separate both transfer function

is this the way to do it..?

Now I have H(s)=D(s)*G(S) ( from picture 3)

And I know the PID gains => I know the 2nd order transfer function of the PID controller ie, D(s)

to get the G(s) I need to divide the H(s) with D(s)

G(s)=[H(s)/D(s)]

Is it right or am i missing something?

Thanks for your help in advance.

This is sundaram, I'm working on a speed control of belt driven drum project and I'm new to control system concepts.

I'm trying to find the transfer function of the system so that I can model it in simulink and tune the PID and look in to other aspects of the system.

The blocks and variable i'm outputting is in the attached Image (picture 2)

http://files.engineering.com/getfile.aspx?folder=a...

The speed loop control (PID) is in the control block and it has a microcontroller in it (where I tuned the system partially).

Now the variable I'm out putting on to the scope is the internal speed var which gets calculated at a rate of 18KHz .

From the over shoots and rise time I could calculate damping ratio and natural frequency in rad/sec

and substitute in the standard 2nd order system transfer function.

But the 2nd order transfer function which I got above includes the PID control which is in the microcontroller.

But to the best of my knowledge it should not be included and it should be separated,then only I can use it in MATLAB.

From the diagram (picture 3) H(s) is the transfer function I have, D(s) is the PID loop and G(s) is the plant model.

http://files.engineering.com/getfile.aspx?folder=7...

Can anyone help me, I'm I right in my approach ?, if so how can I separate both transfer function

is this the way to do it..?

Now I have H(s)=D(s)*G(S) ( from picture 3)

And I know the PID gains => I know the 2nd order transfer function of the PID controller ie, D(s)

to get the G(s) I need to divide the H(s) with D(s)

G(s)=[H(s)/D(s)]

Is it right or am i missing something?

Thanks for your help in advance.

## RE: understanding the system modeling

Search the internet for "closed-loop system identification", as that's what you're trying to do. There are many available resources.

xnuke

"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand,

Atlas Shrugged.Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

## RE: understanding the system modeling

I'm understanding what ur trying to explain, you are right R is step input and y is the output

from picture 4 which I have the transfer function F(S) and need to get G(S)by understanding the concept of "closed-loop system identification" for me to model in Simulink and I know the D(s) as it is the PID loop I use..

I'm I right..?

http://files.engineering.com/getfile.aspx?folder=3...

## RE: understanding the system modeling

xnuke

"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand,

Atlas Shrugged.Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

## RE: understanding the system modeling

1) http://www.ualberta.ca/~slshah/public_share/IDfrom...

2) http://arrow.dit.ie/cgi/viewcontent.cgi?article=11...

3) http://www.mii.lt/informatica/pdf/INFO282.pdf

I feel the paper 1 and 2 have some relevance with what I'm trying to look for

Pl suggest are this ok or you have some thing more simple and I can understand as I'm very new to this field.

Thanks for your inputs.

## RE: understanding the system modeling

## RE: understanding the system modeling

## RE: understanding the system modeling

http://files.engineering.com/getfile.aspx?folder=3...

and as D(s) in the above system to unity or say 1 the F(s) has only G(s) and so the Y(s)/r(s) =G(s).

Sorry if it sounds as a bad idea, but I'm trying to make systems D(s) insignificant so the I can find G(s)... My goal is to get G(s)...

Pl add your thoughts and comments.

Thanks..!

## RE: understanding the system modeling

## RE: understanding the system modeling

## RE: understanding the system modeling

acc = Torque/Inertia and the acceleration integrates to velocity.

## RE: understanding the system modeling