Error using transfer functions

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Shyam
Shyam on 7 Nov 2017
Edited: Ramu Nair R on 1 Dec 2017
Please help me sort out the issue. I am not understanding why the gain block dimension is shown as 2, where as i am expecting only 1. Please see the attached screenshot of simulink blocks.
  7 Comments
Shyam
Shyam on 7 Nov 2017
I get these errors, included in attached screenshot.
Shyam
Shyam on 7 Nov 2017
Edited: Shyam on 7 Nov 2017
Hi, errors are no longer there. I just closed and opened the model. But, as you said, it is running very slow. Any idea, why...? It runs normally if the compensator blocks are not there (2 transfer functions and 1 gain block), which adds to the summer

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Accepted Answer

Birdman
Birdman on 7 Nov 2017
It is normal for simulation to run faster if you substract Transfer functions from the model but the main reason it is slow is that there are too many mathematical calculations to be done and too many states coming up from transfer functions and integrators. The variable-step solver tries to automatically adjust the step size for solving the states but since this model is an electrical system and since naturally electrical systems tends to behave quickly, the solver reduces the step size to almost 1e-4 and this results in simulation to slow. I have some suggestions:
-First, try to find the most suitable sampling time for your model. This means discretizing the continuous blocks in a suitable manner(Transfer Functions and Integrators). Because the variable step solver automatically increases the step size(narrows) in order to give you a solution but this results in slow simulation. I suggest you to look for Bode Plots of Transfer functions and controllers in your model.
-Second, be careful with the potential algebraic loops while discretizing the system.
  11 Comments
Shyam
Shyam on 11 Nov 2017
Thanks, i figured out the issue.
Birdman
Birdman on 11 Nov 2017
I was about to solve it, too. Glad you figured that out.

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More Answers (1)

Shyam
Shyam on 30 Nov 2017
Another problem involving simple transfer function. I have attached the simulink model and init mfile. I am getting the error regarding singularity in the solution.
  14 Comments
Ramu Nair R
Ramu Nair R on 30 Nov 2017
Edited: Ramu Nair R on 1 Dec 2017
I installed latest version and opened the model. I am trying to use memory blocks instead of delay block. Also, is it necessary to use z domain for transfer function. The block is a part of a bigger system, which are in continuous time, fixed step and solver is Runge-kutta
Ramu Nair R
Ramu Nair R on 1 Dec 2017
Edited: Ramu Nair R on 1 Dec 2017
It worked. The problem was with initial condition. Thank you very much for your time and effort.

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