EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Etesla on February 26, 2024, 04:14:06 am
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Hi all,
I'm on a mission to model a transformer with parasitics as well as saturation.
I'm trying to use the LTSpice wiki transformers page here:
https://ltwiki.org/index.php?title=Transformers
but I'm having trouble understanding some of the material. I thought it would be good to model up a totally equivalent transformer using each of the outlined methods, but I only got through two before I got confused.
[attachimg=1]
The first two options for models make sense to me. I'm basically just modeling 'K' in a different way between the two of them. I then got to the third concept where they talk about 'the core' and use a voltage dependent voltage source, and current dependent current source, to try to model a 'single coil', but I'm not sure how to make a transformer equivalent to my first two using this method. This was my attempt:
[attachimg=2]
I can see that the output voltage simulated by the third option does not match the first two, which match each other perfectly.
Can someone help me understand what the 'core' node is all about? What does the voltage at 'C' represent? How is the information about the primary and secondary winding inductance preserved in the third model? Why does the third model result not match the first two?
Thanks in advance!
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The 'core' is where the magnetic fluxes of the primary and secondary basically cancel one another out, hence the two current sources that work to cancel one another, the flux in a transformer core is due to the magnetising current (this current is not implemented in this model) and Np*Ip = Ns*Is, this is because of the flux cancellation effect between primary and secondary currents.
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Ok interesting, so it seems like I lost the ability to model the magnetising current in model #3. Is this the best way to add that effect back in? Just added L12 which I think you would call the mutual inductance referenced to the primary? In this updated version the output voltage again matches the other two versions perfectly so mission accomplished there.
[attachimg=1]
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I guess now I'm confused about the fourth model presented in the transformers page. What is the purpose of 'Lc'? Is it supposed to have an effect similar to me adding L12 in the previous post?[attachimg=1]