simulation discrete-time model

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massimiliano frasca
评论： Star Strider 2019-11-10
I'm studying the linear model of a DC motor. In state-space form, the governing equations above can be expressed by choosing the rotational speed and electric current as the state variables.
So:
Ac = [-b/J k/J; -k/L -R/L];
Bc = [0; 1/L];
Cc = eye(2);
Dc = zeros(2,1);
I expressed all in discrete -time:
sys_TC = ss(Ac,Bc,Cc,Dc);
sys_TD = c2d(sys_TC,Ts);
[A,B,C,D] = ssdata(sys_TD);
Now I shuould simulate the model (TD). In this sense, I simulate the input signal with the function rand. How can I obtain the results of the output and collect them in a matrix?

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Star Strider
Star Strider 2019-11-7
To simulate your system with the appropriate input, use the lsim function. You will need to create a time vector as well as the input signal vector. (You have a single-input system, so this is straightforward. For multiple-input systems, the number of columns in the input signal must match the number of columns of the B matrix.)
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massimiliano frasca
massimiliano frasca 2019-11-10
Thanks for your help, I tried to do how you suggest. How can you see from my question, the output should be a vector with two rows and one column, but when I use the lsim function I obtain a vector with one rows and one column. Did I make a mistake or is is this the output form of lsim function?
Star Strider
Star Strider 2019-11-10
As always, my pleasure!
No, the output should be a matrix of N rows and two columns.
This code:
[u,t] = gensig('square',1,10,Ts);
y = lsim(sys_TD, u, t);
returns a (10001x2) output matrix in ‘y’ when I run it, as it should. If you are not using the gensig function, be sure to create ‘u’ and ‘t’ as column vectors.

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