Can a Level 2-s function block output a transfer function?

I am working on a code whose output is a transfer function. I want to implement this code in Simulink and I am using the Level 2-sfunction block in order to implement it. The main issue is that once the code runs in Simulink. It gives me the following error.

" An error occurred while running the simulation and the simulation was terminated Caused by: Error evaluating registered method 'Outputs' of MATLAB S-Function 'run_1' in 'test/Level-2 MATLAB S-Function'. The following is the MATLAB call stack (file names and line numbers) that produced this error: ['C:\Previous computer\dani usb 2 backup\AUS University\Master\4th semester\MTR 690\MTR projects\Level-2 S function\ninteger\run_1.m'] [219] Invalid assignment in 'test/Level-2 MATLAB S-Function'. Data must be a numeric or logical array Component:Simulink | Category:Block error "

I would like to know if there is a way to output a transfer function using the Level 2-s function block. The reason I need it is because I need to keep on updating variables that need to be fed into the function.

[Birdman]

Can you share your code?

[Danial Waleed]

The code requires other dependent functions in order to work properly. I am sending you the files just extract them and run the test.slx file in order to see the simulink file. The code which the level-2 s function block uses is called run_1.m. thanks for your prompt feedback.

Answer 1

[Birdman]

The problem seems to be with your output. You tried to output a datatype of tf, which is not supported by Simulink. Simulink works only with numerical values, therefore it is possible for you to work with them. In your run_1.m file, I changed the output accordingly. Please check that. I also set the Save output format to Array, in which you can easily see the coefficients being logged at every sample. You can change the formats according to your desire. The key change was this:

 block.OutputPort(1).Data=[y.Numerator{1};y.Denominator{1}];

Hope this helps. Let me know if it works for you.

[Danial Waleed]

The issue with the above approach is that when the inputs value change the size of the transfer function will change as well. Which will create issues in the long run. This is something I would like to avoid. Can you look into the nipid block and see how it is able to produce a transfer function as an output and how I can replicate it with changing inputs.

[Birdman]

What can be the maximum size of inputs?

[Danial Waleed]

In total I need 7 inputs some of the values will change with time namely kp,ki,kd,vi and vd . Honestly I am not sure as to what the maximum expected order will be for the output transfer function. Unless I try all the possible outcomes which is not easy.

[Birdman]

Simulink does not want to work with variable size inputs/outputs. Even if you have a variable sized output, you need to specify an upper limit for it. Therefore, I suggest you to specify an upper limit and work according to that.

[Danial Waleed]

I will see what I can do.

[Birdman]

Ok, looking forward for your further questions.

Answer 2

[Walter Roberson]

No, Level 2 S function must output signals, and tf are not signals. There is provision for creating custom data types for signals but the components are limited to double, int32, logical, char, and char with restricted values

https://www.mathworks.com/help/simulink/ug/simulink-data-class-extension-using-matlab-class-syntax.html

You could potentially create vectors of coefficients and current state and output those to be processed by a later S function or MATLAB Function Block, but you cannot output a tf and you cannot output a Simulink Block as a signal.

In some cases you might be able to use the S function to do the equivalent of set_param or to tune parameters of an existing transfer function block.

[Danial Waleed]

Understood, I think I will look into alternative than using Level-2 s function because there are so many limitations that I believe other alternatives could be better.