State-Space Matrix Closed Loop System C Matrix issue

Question

Pablo Graale 2023-5-30

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1975374-state-space-matrix-closed-loop-system-c-matrix-issue

回答： Pablo Graale 2023-5-31

采纳的回答： Sam Chak

在 MATLAB Online 中打开

Hi, I'm trying to obtain the same output I get with the following commands on Matlab on Simulink.

In Matlab I have the following

% Sistema
A = [-1.15 -0.155 -0.005;1 0 0;0 1 0];
B = [1; 0; 0];
C=[0 0 0.3];
%Espacio de Estados
sys=ss(A,B,C,0);
%% Ecuación deseada
Ps= [1 2 1.5 0.5];
Ed=roots(Ps)
k2 = acker(A,B,Ed)
%% Lazo cerrado
Af=A-B*k2;
%% Calculando los autovalores del sistema en lazo cerrado
eig(Af);
%Condicion inicial
x0=[1 0 1];
%Sistema con realimentación en espacio de estados
slc=ss(Af,B,C,0);
%Respuesta del sistema
figure
subplot(211)
initial(sys,x0)
title('Lazo Abierto (CI)');
subplot(212)
initial(slc,x0)
title('Lazo Cerrado (CI)')

So I obtain the open loop and closed loop responses. In Simulink I've got the open loop answer by inserting a unit step followed by a derivative block.

But here comes the problem, the C matrix is [0 0 0.3] but as I have to introduce the gain, then the dimension of the matrixes on the State Space block have to match. I don't know how to set it up, in order to get the same answer I get from Matlab.

Any idea on how to get that block diagram on Simulink?

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Atsushi Ueno 2023-5-30

The feedback loop (gain k2) must be multiplied against state x, not the output y of the state space model.

I remember what I previously added a comment to another question.

https://jp.mathworks.com/matlabcentral/answers/1968119-error-using-inputoutputmodel-feedback-line-137-the-first-and-second-arguments-of-the-feedback-co#comment_2753754

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Sam Chak 2023-5-30

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1975374-state-space-matrix-closed-loop-system-c-matrix-issue#answer_1246949

编辑：Sam Chak 2023-5-30

在 MATLAB Online 中打开

Hi @Pablo Graale

The output of the state-space system is

. Your Ackermann's controller is full state-feedback, not output-feedback.

Thus, the equivalent Simulink model would look something like the configuration shown in Figure 2.

The state-space slc requires modifications in the C and D matrices.
Set the Multiplication: Matrix(K*u) in the Gain block K2.
This Reference input is essentially zero, not a Step signal (because it is not shown in your equation)

% Sistema

A = [-1.15 -0.155 -0.005;

1 0 0;

0 1 0];

B = [1;

0;

0];

C = [0 0 0.3];

% Espacio de Estados

sys = ss(A, B, C, 0);

% step(sys)

Ps = [1 2 1.5 0.5];

Ed = roots(Ps);

k2 = acker(A,B,Ed)

k2 = 1×3

0.8500 1.3450 0.4950

% Lazo cerrado

Af = A - B*k2;

% Calculando los autovalores del sistema en lazo cerrado

eig(Af);

% Condicion inicial

x0 = [1 0 1];

% Sistema con realimentación en espacio de estados

slc = ss(Af, B, C, 0);

%Respuesta del sistema

figure

subplot(211)

initial(sys, x0), grid on

title('Lazo Abierto (CI)');

subplot(212)

initial(slc, x0), grid on

title('Lazo Cerrado (CI)')

Figure 1: Results from MATLAB.

Figure 2: Simulink model.

Figure 3: Results as seen in Simulink Scope.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Askic V 2023-5-30

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1975374-state-space-matrix-closed-loop-system-c-matrix-issue#answer_1246939

在 MATLAB Online 中打开

This is how I would simulate similar system in simulink.

First of all this is the simulation in Matlab script:

% Transfer function G = 1/((s+1)(s+2)(s+3))

num = 1;

den = conv([1 1],conv([1 2],[1 3]));

% convert to state space

[A,B,C,D] = tf2ss(num, den);

% State space model

sys = ss(A,B,C,D);

% Gain to place closed loop poles at -3,-4,-5

K = acker(A,B,[-3; -4; -5])

K = 1×3

6 36 54

% Close loop matrix A

Af = A-B*K;

%eigenvalues of Af are desired pole locations

eig(Af);

%Initial condition

x0 = [1 0 2];

% State space model of closed loop system

slc = ss(Af,B,C,D);

% Plot responses

figure

subplot(211)

initial(sys, x0)

title('Open loop');

grid on

subplot(212)

initial(slc, x0)

title('Closed loop')

grid on

in order

In order to make Simulink simulation, you need to have state feednack controller, i.e. each gain in the K vector should mulitpy corresponding state variable. However, from the state space Simulink model, you have only output. In my example C vector is [0 0 1], so state variables can be chosen as: x3 = y, x2 = dy/dt, x1 = d2y/dt.

The simulation would look like this:

Please note that in the ss model of the closed loop system, i used Af = A-B*K matrix instead of A.

The outputs are very similar though not the same. I guess it is because of the numerical calculations of derivative blocks in the state feedback loop. To make something more realistic, you should design observer for this system that will have one input (y) and three oututs or output 3x1 (state variables x), and then use gain vector K to construct state feedback loop.