Modelling an AC electromagnet using Comsol Multiphysics

This Comsol tutorial shows how an AC electromagnet consisting of a ferrite core and a coil can be modelled numerically. The 3D simulation is done in the frequency domain (assuming sinusoidal input current). The ferrite core gets magnetized by the magnetic field generated from the alternating current in the coil. Comsol v5.6 is used in this video.
Chapters:
00:00 Geometry
04:08 Materials
04:43 Physics
05:20 Mesh
05:40 Solver settings
06:55 Post-processing
10:38 Animation
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[@diliprana3882]

Thank you so much this video man!! Helped me a lot in learning process :)

[@jh061]

Thank You so much sir

[@KM25263]

Thanks

[@khemrajramsamooj9334]

do you think a simple test in comsol can be done using a cylindrical conductor with a sum of sine waves going through it, and then loop antenna/coil mounted on the outside of the conductor to see if they can read the signal on the line?

[@user-uw7fy5zc7m]

Thank you for the great videos. It's very helpful for new COMSOL users like me:) I also want to see the result animation when the frequency 'f' is smaller than 10hz. But after changing 'f' from initial value 1e^5 [hz] to 5 [hz] , an error window "Failed to find a solution. The relative error (2.1e+02) is greater than the relative tolerance. There was a warning message from the linear solver. Iterative refinement triggered. Returned solution is not converged. Not all parameter steps returned. " shows up.. Could I know what problem is?

[@JafScience]

Can you try changing the electrical conductivity of air from 0 to a small number (like 0.1 or 1)? A value of zero can cause numerical instability sometimes.

[@emilyma1355]

I am so grateful for your tutorials! I'm trying to simulate the same thing using a soft iron core. It seems like the higher electrical conductivity gives very unexpected results. Do you have any advice for how to proceed? Thank you!

[@JafScience]

What kind of unexpected results are you getting? Does the iron core have a BH curve defined? Are there any convergence issues?

[@emilyma1355]

@@JafScienceyeah I wasn't very descriptive.. The simulation is showing a magnitude higher level of magnetic flux density where the coil input/output connects to the rest of the coil. The gradients of the magnetic flux density in 2d plots are very coarse, despite using a very fine mesh. The coil current flow and streamline plots look as expected, though. I changed the electrical conductivity of air to slightly above zero and there were no convergence issues. I set the permeability to be constant 4000 for now instead of using a BH curve. I ended up CADing a physical coil instead, and I got smoother symmetric gradients in my 2D plots, so it is alright if you can't think of anything obvious I might be missing! Thank you for your response! I hope you might make more videos in the future.

[@JafScience]

Sorry for the late reply. The higher magnetic flux at the coil input/output is a numerical error and its presence does not necessarily mean that the solution as a whole is incorrect. Other than that, it's difficult for me to explain the rest of the observations without looking at the model directly. But it seems that you're pushing through with a solution. If you think I can help with something you're free to ask. And I'll try to resume uploading videos in the coming months. All the best!

[@angelcasanova7562]

How would you add a hysteresis curve to this model?

[@JafScience]

You need to run it in the time domain and use the Jiles Atherton model under 'Ampere's law'.

[@Virtueman1]

Great video. However I followed this exactly but I get an error "attempt to evaluate negative power of zero". Have no clue what might be causing it and google is no help :(

[@Virtueman1]

Fixed it! The whole "study" had gotten stuck on old settings/variables somehow. Added anew study and it worked. This is a very fast way of simulating inductors :)

[@BeyondAbsoluteInfinity]

Is there a way to find force in newtons instead of just the flux?

[@JafScience]

There's an option to calculate the total force between magnetic bodies if that's what you're looking for. You can insert it from the physics.

[@BeyondAbsoluteInfinity]

@@JafScience Oh I seee

[@SalmenZ98]

Thank you for the video. What about the way around? I'm trying to simulate a magnetic core around which a winding coil and Apply an external AC current (from a powerline for example, generating an AC magnetic field of course) and see the resulting induced current/voltage from the winding coil. Can you please give me some steps on how to do it? Could you please afford your email, I've few other questions, I would be grateful. Thank you

[@JafScience]

The way you're describing your problem it sounds the same as the video (applying ac current). Or is there something else?

[@SalmenZ98]

@@JafScience ​ @Jaf-Science Thank you for your answer. It's quite the opposite way compared to the video because the coil will induce current instead of supplying a current to it. I will send you a detailed description of the problem via e-mail. I already designed the geometry of the problem yet it's a bit complicated when it comes to physics. I hope you can help. Thanks a lot !!

[@Nami_Jhon]

Hi! When I made this simulation according to the video, there was no magnetic flux in the iron oxygen body in the final result. Which step will cause this problem?

[@JafScience]

Did you use an air volume? If all steps in the video are followed you should get the same results.

[@Nami_Jhon]

@@JafScience Sorry. I'm new to COMSOL ,I don't understand the air volume and which step would use the air volume

[@JafScience]

@@Nami_Jhon Air volume is just a box around the components and we define air properties for it. This would allows the magnetic field to spread in space.

[@shrikrushnasonawane1703]

Great video, Thank you sir. Could we convert this from AC to DC...Is it possible..??

[@JafScience]

If you mean supplying DC current then you can run a stationary study.

[@shrikrushnasonawane1703]

@@JafScience Hii...actually, I tried that but still it's showing the same results...if you could show that part it will be really helpful.

[@JafScience]

If the frequency is low the results may look similar to the static case. Try increasing the frequency and observe if there's noticeable difference.

[@khemrajramsamooj9334]

can this model be used to model a multi-turn loop antenna?

[@JafScience]

For modelling Antennas I believe you need to use the RF module.

[@khemrajramsamooj9334]

@@JafScience Will the RF module work with this geometry? I am trying to design a multi-turn loop antenna using a 200kHz bandwidth in COMSOL.

[@JafScience]

It can work with any geometry as long as the physics is defined properly.

[@khemrajramsamooj9334]

@@JafScience If I use the magnetic field interface, will I be able to obtain a frequency plot?

[@khemrajramsamooj9334]

@@JafScience when modelling a multi-turn loop antenna, I will have to use the magnetic field (mf) interface since I would have to adjust the amount of turns.

[@dinleepound9466]

Hey Jaf! Thanks for your video! Could you also post some links which should be watched prior to this one? I am very new to COMSOL and this video seems to have skipped select "study" or what :-)

[@JafScience]

Welcome to Comsol modelling! The video shows how to add the study at 05:40. If you are asking how to select the study for values of dependent variables at 06:25, then you can select from the drop down list of available studies. In this video, the study "coil geometry analysis" was chosen automatically. I hope this helps.

[@dinleepound9466]

@@JafScience Hey Jaf! Really thanks for your video now I can manage to follow these steps now:) I am also wondering if you can make a video showing how to work with the SPICE circuit in COMSOL?

[@JafScience]

You're welcome! Yes, Comsol has a circuits interface that can model electrical circuits. It doesn't require any geometry. I plan to produce a tutorial soon.

[@dinleepound9466]

@@JafScience Yeah it's a great idea! I don't know if my follow-up comment would be a bit irrelevant here, but actually, I am curious about how to model a magnetic component (like the magnetic core in a converter circuit). Because to perform this kind of modeling in COMSOL, it may require importing the external circuit (maybe from LTspice ) into COMSOL (this is how I see it now). However, I hardly figure these steps out how to combine the circuit in SPICE and COMSOL together. I read some application notes from COMSOL, which says I may need to work with "electrical circuit interface" and "SPICE netlist". But as a lack of an intuitive demonstration, it sounds still vague to me. I would appreciate it if you also have any comments on this question! With regards.

[@JafScience]

Yes you can import a SPICE circuit into Comsol but an easier alternative is to build the circuit in comsol and then couple with another physics interface. You can add voltage/current sources, resistors, capacitors, inductors, transformers, etc. It's actually easy to implement. I plan to make a tutorial of a circuit with resistors/capacitors to demonstrate how a circuit can be built.