Hello,

I have a simple question (but not simple for me):

I would like to create a new component whose output signal follows the input signal with a constant slope (not like the PT1 with exponential characteristics).

For example: the input signal is a step or a ramp from 2 to 7 and the output signal which is supposed to also start at 2 should now move to 7 with e.g. 0.2/sec. As a consequence of course different steps take different time.

Is it possible to model this using standard components from Modelica.Blocks.Continious?

Thank you very much for your help.

david.

Hello David,

a possible solution is to combine a two point static controller with an integrator in a feedback control loop. An example is shown in the attached file.

I had to use a trick. Instead using a two point static controller I used a three point static controller with a very narrow area around zero. This is necessery because when the control error is around zero there occur a lot of events when switching from negativ value to positive value. This results in a dramatic slow down of the simulation.

Regards

Florian

Thank you, Florian.

I tested the model and it works fine if the slope of the output signal is smaller than the slope of the input signal. But when I use a ramp (attached)

offset = 2
height = 7
duration = 10 (>height)

instead of the step this generates too many events, because the

if (u < 1e-4 and u > -1e-4) then

expression chatters.

Do you have any idea how to avoid this?

What I want to do is: the constant-slope-model should represent a motor of a valve with constant speed.
The valve is conntrollesd by a PI-controller. Till now I use a PT1 for the motor delay.

Thank you again,
david.

Hello David,

this is a tricky problem. I think it's quite difficult to a get purely time continous solution for your probelm. I would suggest to use a sampled three point model. I tested it and it seems to work with a ramp. Attached to this post you'll find the package.

Regards

Florian