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Identical models in MATLAB and Simulink do not match each other

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Daniel Gelman
Daniel Gelman on 19 Aug 2016
Answered: Daniel Gelman on 22 Aug 2016
I am noticing that discrete-time models I am using in Simulink do not match the same response in the Matlab environment.
For example.
sys = tf([3.332 4.679], [1 30.97 45.5], 'OutputDelay', 0.1);
sysd100 = c2d(sys,0.01)
sysd200 = c2d(sys,0.005)
figure;
opt = stepDataOptions('StepAmplitude',200);
step(sys, opt), grid on; hold on;
step(sysd100, opt); hold on; step(sysd200, opt);
sys is my continuous transfer function, sysd100 is the same function sampled at 100 Hz and sysd200 is sampled at 200 Hz. The step response is expected. I then reproduces the same transfer functions into Simulink, but am getting the following results
I am not an expert in Simulink so I ask the community on what would be the reason for this behaviour.
Thank you, Daniel

Answers (1)

Daniel Gelman
Daniel Gelman on 22 Aug 2016
[Answered]
Always be aware of significant figures. Even 0.0001 can make a difference in differential equations.

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