Thread Subject: Frequency dependent parameters in Simulink

Hi all,

I am a beginner with Simulink and is trying to build a model of an electromagnetic actuator, single-degree-of-freedom-system. The actuator has frequency dependent resistance and inductance (due to induced eddy currents) and also (I believe) frequency dependent damping (due to structural damping in a mechanical spring). My goal is to get the transfer function of the system (force/voltage) in the relevant frequency range 100-10 000Hz. My source is currently a swept sine (chirp) signal.

My question is how can I implement these frequency dependent parameters? I realize that I need to use look-up tables, but I don’t know how to get the current frequency of the signal during the sweep. Is it possible to use the “invfreqs”-function somehow? Are there any examples avaliable?

Thanks a lot in advance for any help in this,

Johan Gustafsson

Being a time-based simulation package there really isn't a nice way to handle frequency dependent parameters in Simulink.

There are two approaches you could try,
1. perform a system identification on the frequency data to get a time domain model that can then be used in Simulink.
There is functionality in the System ID Toolbox and the Signal Processing Toolbox that should/could be useful for that.
Unfortunately if your data is quite non-linear then it may not give you enough fidelity in the model.

2. write a block/s-function that at each time step calculates an fft of the input signal and try to extract the frequency of the peak of the fft.
Then use that frequency as the input of a look-up table.

Phil.