Why do Transfer Blocks sometimes generate noise ?

Hello,

I often use transfer functions or transport delays to break up algebraic loops in my models. I pay attention to choose time constants and delays which are are multiple of the fastest rate in my simulation.

But sometimes those blocks add peaks to the signals as shown below.

The green signal is the output and the black signal the input of the block depicted on the right side.

Does anybody know why those peaks occur or are there better ways to break up the loops instead of transport delay and transfer functions ?

EDIT:

As requested I added an Example Model. Unfortunatly I only had an example at hand which also uses Simscape electrical Blocks.

I hope this helps never the less.

[Benjamin Thompson]

Please post an example model demonstrating your problem or question.

[Mathieu NOE]

hello

what are your solver options ?

I personnaly prefer to force / use discrete filters and solver is fixed steps. if you use variable step solver options that can sometimes cause trouble. I don't even use variable step option when it comes to signal processing or process simulations

[Matthias Menge]

Hello Mathieu and Benjamin,

than you very much for your quick answers. I added an Example. As mentioned in the Edit it unfortunately uses Simscape Electrical Blocks.

I use the standard solver configuration, but will gladly look into using fixed step solver.

[Mathieu NOE]

hello

sorry but I am not a simscape user... I will not be able to do anything on your model

Answer 1

[Pratik]

Hi Matthias,

As per my understanding, you want to break up algebraic loops in your Simulink model and for that you are using a Transfer function block. However, this block seems to be creating noise in the signal.

If you're observing spikes in the simulation after introducing a transfer function to break an algebraic loop, it's possible that the dynamics introduced by the transfer function are not negligible.

As a workaround, “Transport Delay” block can be used with a very small delay time. For the example model provided a “Transport Delay” block with time delay of 1e-4 works fine.

Please refer to the documentation of “Transport Delay” Block for more information:

www.mathworks.com/help/simulink/slref/transportdelay.html

Please refer to this MATLAB Answers post for more information about algebraic loops and how to solve them:

www.mathworks.com/matlabcentral/answers/95310-what-are-algebraic-loops-in-simulink-and-how-do-i-solve-them

I Hope this helps!