Transport Delay of Zero

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Shane Cheshire
Shane Cheshire on 3 Mar 2020
Commented: Robert U on 4 Mar 2020
I have the following block diagram.
My step input is set to 1000 sec. By changing the TM value in the I'm attempting to get the following graph. One with tm=1000 and the second with tm= 0. This is the graph I'm supposed to get for the block without preditictive control.
Instead this is what I'm getting
I'm getting an error when I set the transport delay to zero, it says that there maybe an algrebraic loop. Any idea how I might fix this?
Jade O'Connor
Jade O'Connor on 4 Mar 2020
It should work if you move the time delay block into the feedback loop :)
Robert U
Robert U on 4 Mar 2020
Hi Jade,
Your suggestion probably does not work, either, when setting the time delay to Zero.
Kind regards,

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Answers (1)

Robert U
Robert U on 4 Mar 2020
Edited: Robert U on 4 Mar 2020
Hi Shane Cheshire,
There is plenty of hints in Matlab documentation on how to fix algebraic loops. Most conveniant is to introduce a unit-delay block that will delay the feedback signal by one time step. That usually does not have any significant impact on the simulation result.
Another option is to use very small signal delay times. But this option might increase simulation time dramatically.
Kind regards,

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