Discussion Forum

Hi

I think I have some input regarding the calculation of the inductance that could be of interest. Comsol is quite new for me so I'm not an expert on this, but I have been looking at how to calculate the induction and the mutual induction in coils. I'm working at version 4.1 so I'm not sure what the different between the versions are, but in a 2D-axial symetric model with coil domain the v4.1 will generate the matrix automatically (mef.Lc_1).

If you have to calculate it "manually" you can calculate it by using the simulated voltage drop in the coil by using the formula L=(1/mef.omega)*imag(Vtot_1/I1) (I assume that you simulate it in the frequency domain). You can find an example in my poster dated April 21, 2011 4:07pm.

As you mentioned a method is described in the AC/DC which is the energy method. You will find a good example on this under www.comsol.no/showroom/documentation/model/4329/. I tried this method but the results didn't match the induction matrix calculated automatically by Comsol.

Regards Yngve

Thank you Yngve,

Just few question. I have version 4.1. But when i define a three turn geometry with each turn as a single turn coil domain and excite one coil with 1 [V] and others with 0 [V] then in mef.Lc_1 I only get self inductance. Please help where i am going wrong. Like you said it can calculate whole matrix. This feature I am desperately looking for. Because i have to calculate on a wide frequency range and my number of turns are quite high in actual model. So it is practically not suitable to calculate each inductance by energy method.

thanks


Omar

Hi

have you also checked the coil grouping BCs (for several single coil loops, also with return current) this gives you common loop voltage access

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Good luck
Ivar

Hi Ivar,

Thank you for your response. I am sorry, I have actually modeled on 4.0a. I cannot find a the 'coil grouping BC' in this version. OK lets start from a very simple case of two coil.

First let me explain what I am doing then I would like your comments.

1. A two coil system is modeled in axis symmetric with two circles.

2. mef physics is selected

3. Terminal BC is assigned to both the coils

4. 1[A] current is assigned to each terminal BC.

5. I am solving in frequency domain

6. Both coils are assigned single turn coil domain with 1 [A] excitation

Now, the problem is that when I solve it then in the first place it gives me an error that solution cannot be found. Secondly, when I go to global evaluation then I cannot see the whole impedance matrix.

Please help where I am going wrong


thanks

Omar

Hi Ivar,

Can you please check my file. Please let me know if this is the right way to calculate the lumped parameters.If so then how would i calculate the inductance matrix. As per my understanding, since this model is giving me the admittance matrix i have to inverse it to find Impedance matrix and then divide the imaginary part of impedance by angular frequency to get the inductance.

If this is the case then I am getting wrong inductances.

Also there is one more question in order to find the impedance matrix directly when i give 1[A] terminal input then an error shows up which says ' Feature stationary solver 1 (sol1/s1) and failed to find a solution'

Please help.


thanks


Omar

Hi

I'm not sure if I understand you correctly. Is a 3 turn coil or is it 3 single coils? Do you want to find both the self inductance and the mutual inductance between the coils? Are you trying to simulate the example in the attached article?

I don't think this will give you all the answers, but I hope it will give you som hints. I have done some changes in your model where i have put in some suggestions. I didn't compile it due to that I have v4.1.

Regards Yngve

Hi Yngve,

Thank you so much. I really appreciate it. You are right I am trying to simulate the model in the paper you attached. The problem is that when follow the procedure in the paper I get good results, which matches with the paper.But when I do the port sweep to find the inductance matrix in one go, then I get wrong results. I mean they dont match with the paper results.

I really need to understand the port sweep method for inductance matrix calculation because if i follow the method presented in the attached paper then it will take a lot of time to find the inductance matrix of a big system and it becomes even a nightmare when I need to find inductance matrices at a range of frequencies.

This is why i really need to understand the port sweep method. My gut feeling is that it is do able.

As for the file i cannot open it because I have older version. May be I should buy 4.1 or if there is any way I can see the edited file in 4.0a.

thanks for your efforts. Looking forward to hear from you.

Regards,

Omar

Hi Omar

Your problem has similarities with my problem. I did the same as you where I tried to simulate the model in the article. To do this you have to make a "dummy" line to define the area where you like to evaluate the flux and then do a line integral over that line. The problem is that i didn't find a good way to generate this as a lumped parameter.

I think the solution for you is to have two physical interfaces in your model. The best for you is to get more specific feedback so I will try to see if it is possible for me to save the model as earlier versions. I will try to give you a feedback within tomorrow or Saturday.

Regards Yngve

Hi Yngve,

Thanks for your reply. I have now version 4.1. I checked the attached file. Actually, problem is not that I cannot find inductance (self or mutual ). My problem is that how to find complete matrix in one shot using terminal boundary condition. Like in electrostatic mode I can find the whole capacitance matrix in one simulation. I dont need to find each element of the capacitance matrix individually. I want to do the same thing for inductance matrix in mef physics.


regards

Omar

Hi

I'm sorry for the misunderstanding. I don't think it is possible to find the complete matrix in one simulation of the same model. At least I haven't found out how to do it. If it is possible then I would believe that you have to excite a current on both coils at the same time, this is described in more details in attached article on page 4 . Anyway the way I solved (I think I have solved it) was to add more models. In my case have 4 different cases where:

1. Open circuit simulation where I calculate the mutual inductance in air
2. Open circuit simulation where I calculate the mutual inductance in water
3. Short circuit simulation where I calculate the self inductance in the secondary coil using the results from model 1
4. Short circuit simulation where I calculate the self inductance in the secondary coil using the results from model 2

There might be a better way to do it, but it seems to work. I hope this will give you some hints. Please let me now if you see any errors in my models.

Regards Yngve

Dear Yngve,

I gotta ask you some questions about finding inductance by using the common formula as "(1/mef.omega)*imag(mef.Vtot_2/Iprim)"

I was wondering where the effect of length of the coils is taken into account in the model; i.e. the induced voltage unit in the coil is Volt by default, but shouldn't it be dependent on the length of the conductor?

Regards
Mamad

Hi,

I wanted ask you something about your model since I am also doing something similar.

As per your points 1 to 4,

1,2. Is the global evaluation for L1 the mutual inductance of the to windings? In that case, I think it should be the same value even if you interchange the excitations (since M12=M21), which is not happening when I exchange the primary and secondary excitations. Please comment.

3,4. You said you calculate the self inductances from your model 1 and 2 results. How exactly is that?

I would be extremely grateful if you replied.

Best Regards.
Shawon.