LQR Error about controllability

조회 수: 28(최근 30일)
Usman Shahzad
Usman Shahzad 2012년 12월 2일
댓글: 嘉俊 黄 2022년 3월 21일
Hi everyone,
I am doing some work on LQR controller for time variant system. My problem is that by choosing the weights Q and R some of my states get worked but some does not. MATLAB gives the error that:
The "lqr" command failed to stabilize the plant or find an optimal feedback gain. To remedy this problem:
1. Make sure that all unstable poles of A are controllable through B (use MINREAL to check)
2. Modify the weights Q and R to make [Q N;N' R] positive definite (use EIG to check positivity).
My question is how i can remove this problem as [Q N;N' R] is sure positive definite and my system is controllable as well.
  댓글 수: 1
Muhammad Ali
Muhammad Ali 2014년 11월 2일
I am facing the same problem as Usman suggested. Please someone answer the queries. Thnx

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Ursula 2013년 5월 24일
편집: Ursula 2013년 5월 24일
I have the same problem. The error message appears, although my system is controllable, and my [Q N;N' R] is positive definite. If I want to get the controller with pole placement, Matlab says:
The "place" command could not place the poles at the specified locations.
Probable causes include:
* (A,B) is nearly uncontrollable
* The specified locations are too close to each other.
The specified locations are at -1, -2, -3, ... -59, and there is no other result, if I increase the space between the desired poles.
My System is of 59th order. The maximum value of Matrix A is 3e+006 and the Controllability Matrix of (A,B) has maximum value of 3e+120. Is this maybe a numerical problem, and how can I solve it?
  댓글 수: 3
嘉俊 黄
嘉俊 黄 2022년 3월 21일
OK,Thank you!

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Leonardo Costa
Leonardo Costa 2021년 1월 31일
Hi, I'm facing the same problem! Did you solve it?

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