du/dt avoiding in system

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Marcel Büttner 2015-6-28

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评论： Marcel Büttner 2015-6-29

采纳的回答： Stefan

Is there any possibility to solve

x = L*y*s + 2*y , without a du/dt block. ..

(x:output ; y:input)

Just e.g. integrators.

My system is very dynamic and du/dt would cause errors.

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Walter Roberson 2015-6-29

Under what circumstances would you get an error from the du/dt block?

Marcel Büttner 2015-6-29

The values would rise too high. The simulation stops cause of infinity.

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Stefan 2015-6-29

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编辑：Stefan 2015-6-29

Two remarks here:

1. If you draw the Bode plot of the transfer function of the derivator, it looks like a line that ramps up with 20 dB/decade. In other words, for high frequencies it amplifies the signal (most likely it is a noise in this region). So, what you want is to avoid this phenomena, however keeping the derivator behavior for lower frequencies. In order to achieve this, replace your derivative block with a transfer function block:

where you have to choose tau sufficiently low. Notice that if tau = 0, then you end up with the derivator H(s) = s.

2. You say something about using integrators. This is possible if you solve your equation the other way around, namely you know x and want to calculate y. The dynamics of y is described by:

dy/dt = (1/L) (2y-x)

For this, you need to know the initial condition y(0) of your system, together with x(t). You code this equation in matlab or Simulink using an integrator block.

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Marcel Büttner 2015-6-29

Perfectly explained. Thanks Stefan

Marcel Büttner 2015-6-29

The second remark is not right for this question, cause your input is y and your output is x . As you explained I could only get y as an output value.

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