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Simulation of a wireless power system

Posted Apr 16, 2013, 9:11 a.m. EDT Low-Frequency Electromagnetics Version 4.3a 11 Replies

Oskar Rönnbäck
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Hi,

I am trying to simulate a wireless power system between two coils. The transmitting coil is connected parallel to a electric circuit consisting of a capacitor and a voltage source in parallel. I think this part is working.

The receiver coil is connected to another electric circuit consisting of a capacitor and a resistor.

I want to simulate the transmitted power, transfer efficiency, mutual inductance, resonance frequency. But I am not sure how to do this. Any help would be appreciated.

An other issue I came across is the current in the transmitting coil seem way to low. The voltage source is 50V AC and the current is only about 1A and the coil resistance is really low.

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11 Replies Last Post Oct 28, 2015, 10:31 a.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 16, 2013, 2:00 p.m. EDT

Hi,

I had a look into your model. A hand calculation shows that the transmission coil has an inductance of 345 nH, this translates to a reactance of roughly 22 Ohms at 10 MHz. And you have to consider the skin effect at that frequency.

Cheers
Edgar

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Edgar J. Kaiser
www.emphys.com
Hi, I had a look into your model. A hand calculation shows that the transmission coil has an inductance of 345 nH, this translates to a reactance of roughly 22 Ohms at 10 MHz. And you have to consider the skin effect at that frequency. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Oskar Rönnbäck
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Posted: 1 decade ago Apr 17, 2013, 2:46 a.m. EDT
Thank you for your answer,

The transmission is suppose to be driven at resonance where the inductance and capacitance cancel out leaving just the ac resistance in the coil. I realized that I did not have the right resonance frequency so the problem with the low current is fixed.

Does Comsol take consideration of the skin effect automatically? Or do you have to put it in manually?

I have updated my model is the efficiency plot (1D plot group) made properly?

Thank you for your answer, The transmission is suppose to be driven at resonance where the inductance and capacitance cancel out leaving just the ac resistance in the coil. I realized that I did not have the right resonance frequency so the problem with the low current is fixed. Does Comsol take consideration of the skin effect automatically? Or do you have to put it in manually? I have updated my model is the efficiency plot (1D plot group) made properly?

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Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 17, 2013, 3:10 p.m. EDT

The efficiency plot looks ok. The skin effect is considered, but you must take care about the meshing. You need a couple of elements across the skin depth. If the skin depth is too small to resolve it (probably the case with Cu at 10 MHz) by the mesh you can apply an impedance BC.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
The efficiency plot looks ok. The skin effect is considered, but you must take care about the meshing. You need a couple of elements across the skin depth. If the skin depth is too small to resolve it (probably the case with Cu at 10 MHz) by the mesh you can apply an impedance BC. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Oskar Rönnbäck
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Posted: 1 decade ago Apr 23, 2013, 9:48 a.m. EDT
I have put some boundary layer across the skin depth. What would an impedance BC help with?

I tried to expand my model with multiple turn coils, using multiple turn coil domains. But I get an error I can't figure out. New model attached.
I have put some boundary layer across the skin depth. What would an impedance BC help with? I tried to expand my model with multiple turn coils, using multiple turn coil domains. But I get an error I can't figure out. New model attached.
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 23, 2013, 10:32 a.m. EDT

You haven't assigned any materials.
With the Impedance BC you can avoid to mesh the interior of a conductor, but I am not sure if it is consistent with the multiturn coil domain.

Cheers
Edgar

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Edgar J. Kaiser
www.emphys.com
You haven't assigned any materials. With the Impedance BC you can avoid to mesh the interior of a conductor, but I am not sure if it is consistent with the multiturn coil domain. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Oskar Rönnbäck
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Posted: 1 decade ago Apr 24, 2013, 4:08 a.m. EDT
Thank you for your reply's.

Even with materials assigned I get the following error:

Circular variable dependency detected.
- Variable: mod1.mf.VCoil_2
- Geometry: 1
- Domain: 3

And I can't see why.

Thank you for your reply's. Even with materials assigned I get the following error: Circular variable dependency detected. - Variable: mod1.mf.VCoil_2 - Geometry: 1 - Domain: 3 And I can't see why.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 24, 2013, 5:44 a.m. EDT
Hi

it could be a variable name conflict, if you have not set up explicitely a circular dependence. If you have a non linear model that loops around, often to "open the circular reference" is to adda dependent variable for thsi variable and use that in the moeling

More on this in the Forum, try a search, and in the KB (knowledge Base)

--
Good luck
Ivar
Hi it could be a variable name conflict, if you have not set up explicitely a circular dependence. If you have a non linear model that loops around, often to "open the circular reference" is to adda dependent variable for thsi variable and use that in the moeling More on this in the Forum, try a search, and in the KB (knowledge Base) -- Good luck Ivar
Oskar Rönnbäck
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Posted: 1 decade ago Apr 25, 2013, 4:32 a.m. EDT
The strange thing is when I use the exact same circuits but have single-turn coil domains it works perfect.
Then I change the geometry a bit and put multi- turn coil domains, when i compute it i get the circular dependence error.

I tried the coil group domain and draw the geometry for each turn, but I didn't get the resonance frequency I was expecting.
The strange thing is when I use the exact same circuits but have single-turn coil domains it works perfect. Then I change the geometry a bit and put multi- turn coil domains, when i compute it i get the circular dependence error. I tried the coil group domain and draw the geometry for each turn, but I didn't get the resonance frequency I was expecting.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 25, 2013, 7:02 a.m. EDT
Hi

it looks like some issue with multiple circs and multiple coils, I would suggest that you send it over to "support" to see if they can have a closer look


Another point, for your coil circles, try to add a little air in-between, and do not have the two "just" adjacent with a point contact

--
Good luck
Ivar
Hi it looks like some issue with multiple circs and multiple coils, I would suggest that you send it over to "support" to see if they can have a closer look Another point, for your coil circles, try to add a little air in-between, and do not have the two "just" adjacent with a point contact -- Good luck Ivar
Oskar Rönnbäck
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Posted: 1 decade ago Apr 29, 2013, 7:50 a.m. EDT
I put a 0 Ohm resistor in series with the capacitor and that solved the circular dependency error.

But I get a uniform current distribution in all coils and that can't be true.
Does anyone know where this comes from?
I put a 0 Ohm resistor in series with the capacitor and that solved the circular dependency error. But I get a uniform current distribution in all coils and that can't be true. Does anyone know where this comes from?
Syahid Rohmatulloh
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Posted: 9 years ago Oct 28, 2015, 10:31 a.m. EDT
Hi, have you found the final solution? Because I experience the same problem.
Hi, have you found the final solution? Because I experience the same problem.

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