Simulink error: Time-Varying State Space block

Question

John 2023-3-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1930930-simulink-error-time-varying-state-space-block

评论： John 2023-3-22

采纳的回答： Sam Chak

simulinkPost.m

在 MATLAB Online 中打开

I have a Simulink error I can't figure out, relating to the Time-Varying State Space block dimensions.

I'm using this block so that i can also get x : normal SS block doesn't output x.

This is a simple 2x2 system, and the system dimensions are correct, but I'm getting a port dims error -- it seems to be Output Port 2 (the length-2 "x" output). It could be any system, i happen to have a closed-loop state space, but anything triggers the same error.

Any thoughts why?

I've spent way too much time trying to figure out what's going on...

SL model attached, and Runnable code below.

Error:

Matrix multiply dimensions propagation error. Error occurred while setting output port of 'LQR_post/Varying State Space/Product1' to have the dimensions [1 x 2]. A possible cause for this error is that these dimensions do not agree with the partial dimensions information present on other ports

Component:Simulink | Category:Model error

Error in port widths or dimensions. 'Input Port 2' of 'LQR_post/Varying State Space/Sum' is a [1x2] matrix.

Component:Simulink | Category:Model error

Code:

J = 1e-5;
b = 0.0016;
k = 0.632;
A = [0, 1; -k / J, -b / J];
B = [0; 1 / J];
C = [1 0];
D = [0];
sys = ss(A, B, C, D, ...
    'StateName', {'x', 'x dot'}, ...
    'InputName', {'r(ref)'}, ...
    'OutputName', {'theta'});
Q = [1000 0 ; 0 0.001];
R = [ 0.01 ];
[K_lqr, S1, P1] = lqr(sys, Q, R);
sys_lqr = ss(sys.A - sys.B * K_lqr, sys.B * K_lqr * [1;0], sys.C, sys.D);
sys_lqr.StateName = {'theta', 'angVel'};
sys_lqr.InputName = {'r(ref)'};
sys_lqr.OutputName = {'theta'};
sys_lqr
sys_lqr =
 
  A = 
                theta      angVel
   theta            0           1
   angVel  -3.162e+07  -3.261e+04
 
  B = 
              r(ref)
   theta           0
   angVel  3.156e+07
 
  C = 
           theta  angVel
   theta       1       0
 
  D = 
          r(ref)
   theta       0
 
Continuous-time state-space model.

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Answer 1

Sam Chak 2023-3-18

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在 MATLAB Online 中打开

Hi @John

If you want to get the state vector x, then you can consider this approach because the output vector y can be constructed from the state vector info. In your case,

.

J = 1e-5;
b = 0.0016;
k = 0.632;
A = [0, 1; -k/J, -b/J];
B = [0; 1/J];
C = eye(2);     % Change the Output Matrix to an Identity Matrix
D = [0; 0];
Q = [1000 0; 0 0.001];
R = [0.01];
K = lqr(A, B, Q, R)
K = 1×2
  315.5964    0.3245

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Sam Chak 2023-3-22

Hi John,

The Varying State Space block is actually a Block Mask. If you look under mask, you will see the fundamental blocks of the State-Space. It is important to understand how the matrices work in the State-Space.

By default, the option "Interpret vector parameters as 1-D" in the Constant Block is checked. Because we want the Constant block to treat that specified vector as a matrix, this option must be unchecked.

John 2023-3-22

@Sam Chak, ah, thanks. That clarifies. So the output is x (assuming D = 0) as long as C = I. So fundamentally, the State Space block has x available for the output. Thanks :)

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Answer 2

Paul 2023-3-18

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Hi John,

In the Constant blocks for sys_lqr.B and sys_lqr.C try clearing the block parameter "Interpret vector parameters as 1-D — Treat vectors as 1-D"

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Paul 2023-3-21

The error messages talk about a [1x2] matrix. For what Simulink calls 1D signals Simulink tries to infer dimensions. For example, those 1D signals indicated with a "2" on the signal line could be interpreted as either 1x2 or 2x1 and Simulink tries to figure that out. I thought it likely there was an issue with Simulink not being able to figure out which. By unchecking that box you take away that flexibility and it makes it easier for Simulink to figure out what's what. One tradeoff is matrix signals get logged as 3D, as discussed in your other question.

John 2023-3-22

That's very helpful; thanks @Paul.

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