Error using transfer functions
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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.
采纳的回答
Birdman
2017-11-7
0 个投票
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 个评论
Shyam
2017-11-7
Birdman
2017-11-7
Ok, let me know the results.
Shyam
2017-11-7
Birdman
2017-11-7
What are your controller parameters, J, B, Jem and Bem?
Shyam
2017-11-8
Birdman
2017-11-8
Firstly, how did you select your Kp and Ki parameters? They were not realistic and eventually I had to decrease them. The reason that it gives error for their initial values is that your control signal rises so quickly that the solver step size can not adapt to its quickness no matter how it tightens the step size. Therefore, one solution would be to decrease the controller parameters. I dropped Ki to 70 and Kp to 5. Still, there is an unstable response, which you need to check out. You may resdesign your controller. Please do not pick the controller parameters randomly. Hope this helps.
Shyam
2017-11-8
Birdman
2017-11-8
Ok, let me know the results.
Shyam
2017-11-11
Birdman
2017-11-11
I was about to solve it, too. Glad you figured that out.
更多回答（1 个）
Shyam
2017-11-30
0 个投票
14 个评论
Birdman
2017-11-30
I solved it by changing your solver to Fixed-Step and adding some delays to prevent algebraic loop. But please make sure that your model is reasonably defined.
Birdman
2017-11-30
Values that will not cause algebraic loop. You do not need to change to slx.
Shyam
2017-11-30
Birdman
2017-11-30
No, you have to download it first to your computer. Then open it at Simulink :)
Shyam
2017-11-30
Shyam
2017-11-30
Birdman
2017-11-30
What is your MATLAB version?
Shyam
2017-11-30
Birdman
2017-11-30
Then you can easily open this one in the latest version. Therefore I am not sending the exported version to R2016b.
Shyam
2017-11-30
Ramu Nair R
2017-11-30
编辑：Ramu Nair R
2017-12-1
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
2017-12-1
编辑：Ramu Nair R
2017-12-1
It worked. The problem was with initial condition. Thank you very much for your time and effort.
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