how to choose LQR

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tesem - 2020-12-16T10:54:20+00:00
Question: how to choose LQR

 i am trying to use LQR controller i simulate my system and have my A and B matrix ,, used theme in m-file and use the lqr function to control this system,,, is there any way to know what is the right value for Q and R ?? i try a lot of values for them but the results give me 2 positive values and that is wrong, all values must be negative depending on the choice of the Q and R. so is there any way make me know what is the right values for them instead of try and error ? please help

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    • Expert Answer

    Profile picture of Prashant Kumar Prashant Kumar answered . 2025-11-20

    LQR always returns a stabilizing feedback gain.
    Are there 1 or 2 eigen values that are always show up positive?
    You most likely have an uncontrollable mode in your system. As Azzi mentioned you have to just try different weights, choosing Q and R is part art, part science.
    If you can provide the state space (A,B,C,D) for your plant, it would be useful.


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