Differences in simulation results in state space models using matlab
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Hi,
I'm writing some code to simulate a relay dynamically. I've derived differential equations, linearised them around an operating point and put into state space form. Firstly, I checked the impulse and step response at the operating input using the state space function in matlab, the response was ok. I then implemented the same equations in code (see attached) and the impulse response is different, in fact unstable - any ideas anyone?
Cheers,
Andy
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Suneesh
2013-12-12
You are using continuous SS coefficients while you are (discrete) simulating your system in:
% Perform the system simulation:
x = x0; % Set initial state
for n=1:Ns-1 % Iterate through time
y(n) = C*x + D*u(n); % Output for time n-1
x = A*x + B*u(n); % State transitions to time n
end
y' % print the output y (transposed)
%plot(y')
Instead use the discrete coefficients, which you already have available in 'sysd':
discA = sysd.a;
discB = sysd.b;
discC = sysd.c;
discD = sysd.d;
Then try:
x = x0; % Set initial state
for n=1:Ns-1 % Iterate through time
y(n) = discC*x + discD*u(n); % Output for time n-1
x = discA*x + discB*u(n); % State transitions to time n
end
y' % print the output y (transposed)
%plot(y')
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