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calculate output(y) from a state space model

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I have defined a first order system in state space. How can I calculate Y matrix, if X matrix known
X'=Ax+Bu; Y=Cx;
I attempted to convert the system to a transfer function using tf command. Then can calculate output by y= tf * u The output matrix appears to be in tf data type. I would like to have y in the same data type as x. (full m file attached, following code is an extract of the state space portion)
%Filter Parameters
Lf= 8e-3; % Inductance for output filter
Cf= 400e-6; % Capacitance for output filter
% state space equations for LC filter
A=[zeros(3,3) eye(3)/(3*Cf) -eye(3)/(3*Cf); -eye(3)/Lf zeros(3,3) zeros(3,3);
eye(3,3)/Lload zeros(3,3) -eye(3)*Rload/Lload]; % systemmatrix
B=[zeros(3,3); eye(3)/Lf; zeros(3,3)]; % coefficient for thecontrol variable u
C=eye(9); % coefficient for the output y
D=[zeros(9,3)]; % coefficient for the output y
Ks = 1/3*[-1 0 1; 1 -1 0; 0 1 -1]; % Conversion matrix to transform [iiAB iiBC iiCA] to [iiA iiB iiC]
%Transfer function for inverter output stage
sys= ss(A,B,C,D);
H=tf(sys);
% calculating filtered output
Y=H(1,1) * V_AB;

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Accepted Answer

Honglei Chen
Honglei Chen on 30 Dec 2013
Once you get the model, sys, you can use lsim to simulate the system behavior. You can find details here
HTH

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Rashmil Dahanayake
Rashmil Dahanayake on 31 Dec 2013
Thanks. [y t]=lsim(sys,u,t) command worked well.

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