Transfer Function of a simple Circuit using Simulink

I have a simple circuit for which I just need to obtain transfer function using Simulink. I have attached the image below. Any help would be appreciated. Thanks

http://obrazki.elektroda.pl/7608514200_1400978484.jpg

Answer 1

[Arkadiy Turevskiy]

You did not specify which transfer function you want. Let's assume you want a transfer function from input voltage to output voltage.

1. Start a new Simulink model and add Capacitor, Inductor and Resistor blocks from Simscape, Foundation Library, Electrical, Electrical Elements:

2. Add Controlled Voltage Source block (from Electrical Sources sublibrary) for providing input voltage, Voltage Sensor (Electrical Sensors sublibrary) for measuring output voltage, also add Electrical Reference (ground) (Electrical Elements sublibrary) and Solver Configuration block (Utilities sublibrary in Simscape). Connect the blocks as shown in your image, and specify all the values as shown in the image.

3. Add Simulink-PS Converter and PS -Simulink Converter blocks (also from Utilities sublibrary) for converting Simulink signal to physical signal and back. Use Step block as an input to the model, and Scope as the output.

4. Now right click on the line coming from Step block, and select Linear Analysis Points - Input Perturbation. Right click on the line coming from PS-Simulink Converter block and select Linear Analysis Points - Output Measurement. Note that this requires a license of Simulink Control Design .

5. In the menu select Analysis - Control Design - Linear Analysis

6. In the Linear Analysis Tool click on Linearize:

This linearizes the model, plots the step response (or some other graph if you selected something else, Bode plot, for example) and adds a computed linear system to Linear Analysis Tool workspace:

8. Copy linsys1 to MATLAB workspace (drag and drop in Linear Analysis Tool).Now you can look at the formula and use the linear system for further analysis and design

[Adnan]

 I will test this out. Thanks a lot for your effort and patience.

[Adnan]

Also could you tell me how I would be able to find the Voltage across Individual components, such as inductor if the input voltage is (s+1)/s ? It would be amazing if you could let me know. Thanks again for the effort

[Arkadiy Turevskiy]

I am not sure what you mean when you say the input voltage is (s+1)/s - that expression seems like a transfer function, not a voltage input.

In general to find any voltage for any components, you would construct your circuit like shown above using only the needed components. You can modify the inout signal to the model to be any arbitrary signal. In the example above I used the Step block, but you can use any other blocks from Simulink Sources library to create arbitrary input signals.

[Robert Payne]

I did everything you did and it will not come up with a transfer function. I can't figure out what I did wrong. Any help would be greatly appreciated now. Thank you

[Rajan Kumar]

Dear Sir, Really a nice solution. Can we derive the transfer function of a practical transformer (V_out/V_in), following the given solution? I tried but failed. Please reply.

[Arkadiy Turevskiy]

@ Robert Payne.

I downloaded your model, open Linear Analysis Tool, and linearized the model just fine.

I get this:

[Arkadiy Turevskiy]

@ Rajan Kumar:

If the transformer only has passive elements - yes. If it has power semiconductors, then this approach will not work, as power semiconductors are essentially swithces with discontinuities and cannot be linearized. In that case you will need to use ac sweep approach - see my other comment below.

[Kashif Mehmood]

@Arkadiy Turevskiy

Dear sir i have succesfully simulated your example.its really a nice example to understand.

i want to find out the transfer function of this circuit can you help me please .i have followed the steps but getting errors

[Kashif Mehmood]

@ Rajan Kumar

did you get transfer function of the transformer

[karan kedia]

thank you for the step by step instructions.

Answer 2

[Luigi Dilan Gervasio]

Sorry, I can obtain a symbolic transfer function without specific value of my component?

[Luke Rucker]

This is the real question.

[fima v]

yes i will be happy to have a parametric transfer function

[Arkadiy Turevskiy]

No, creation of a symbolic transfer function from a Simscape model is not supported.

Answer 3

[Azzi Abdelmalek]

Do you want to simulate this circuit with Simulink? If yes , you will need a simscape toolbox

[Adnan]

I already have the Simscape toolbox just need step by step advice as I'm new to this

Answer 4

[Nguyen Dinh Thuc]

From input "Step" to output "PS-Simulink Converter":
    1000 s + 5e06
---------------------
s^2 + 6000 s + 2.5e07

Name: Linearization at model initial condition Continuous-time transfer function.

That is my result, I don't know why, please help me

[Arkadiy Turevskiy]

you got a transfer function, what's the problem?

Answer 5

[Harshit Derasari]

can u give any suggestion how to get transfer function of this circuit???? which i attached here... as per the above steps i not able to attach PS-simulink converter... here DC input voltage is 12v and output of buck converter is around 6v with 50% duty cycle.. inductor of 1mH capacitor of 220uF and R is 10 ohm and i want transfer function from output to input

[Dan Herbison]

Switching circuits do not have "small signal transfer functions", as they are depend fundamentally on large signal circuit behavior. There are several ways of doing what you want, from using an "average model" of the power stage, to using a simulator like Simplis or Saber that handle switching circuit analysis well.

[Arkadiy Turevskiy]

Simscape Electrical handles switching circuits just fine. For a power electronics model with switching from power semiconductors, you will need to use an ac sweep. As switches like diodes are discontinuous, you cannot linearize them. To approximate your model with a transfer function, you inject a small signal (ac sweep) into your system, and compute frequency response from the input to the output. Once you have the frequency response, you can fit a transfer function to it.

This workflow is shown in this example.

[Preeti Warrier]

@Arkadiy Turevskiy

Sir I opened your example iddemo_boost_converter and tried to do what is explained. The figure in your explanation has a voltage sensor and PS-SIMULINK converter, but when I open the model, it is slightly different. It does not have a ground connection, and there is voltage measurement which is connected to the scope. When I run your code to compute discrete points on the frequency response,([sysData,simlog] = frestimate(mdl,ios,in)...,I get these errors.. Index exceeds matrix dimensions.

Error in frestimate>LocalConstructIOTable (line 875)

table{ct,2} = ph.Outport(io(ct).PortNumber);

Error in frestimate>LocalSetupForSimulation (line 435)

table = LocalConstructIOTable(io,ModelParameterMgr,opts)

I changed the outpot port to Uout instead of PS-SIMULINK converter, as the model which opens has only Uout.But still error is there.Please could you guide?

Thanks.

Answer 6

[Kashif Mehmood]

is this possible to find the transfer function of this circuit i have tried alot to find it .please help i want to find i2/i1 . m is the switching function alpha is the thyristor angle

Answer 7

[Adilson Batista]

Help me please. I don't understand step 4. And, I can see the Simulink Menu showed in step 5.