du/dt avoiding in system

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.

[Walter Roberson]

What you posted looks like it only needs multiplication and addition, not integration or any du/dt block.

[Marcel Büttner]

It looks like the following.

What I do not really know is how to prevent my system of errors, when I use the du/dt

[Walter Roberson]

I think you were intending to attach an image?

[Marcel Büttner]

yes sorry I attached it now

[Walter Roberson]

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

[Marcel Büttner]

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

Answer 1

[Stefan]

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.

[Marcel Büttner]

Perfectly explained. Thanks Stefan

[Marcel Büttner]

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.