Electronics > Projects, Designs, and Technical Stuff

Arbitrary (saturable) coupled inductors in LTSpice

<< < (3/5) > >>

uer166:
"Have you tested in the nonlinear region?"

Oh yes, in simulation the saturation looks great, very similar to real-world trace (albeit of another core).

I don't have these specific cores yet but the non-linear region seems to be accurately simulated, which is what I care about most in this application.

Jay_Diddy_B:

--- Quote from: ahbushnell on June 26, 2019, 12:03:40 am ---Looks linear.  Have you tested in the nonlinear region?  Validated with real parts? 

Looks good.



--- End quote ---


The Square Orthonal  material is normally used in special applications. The Magnetics Inc website says:

[b]Square Orthonol

[/b]Square Orthonol, a grain-oriented 50% nickel-iron alloy, is manufactured to meet exacting circuit requirements for very high squareness and high core gain, and is usually used in saturable reactors, high gain magnetic amplifiers, bistable switching devices, and power inverter-converter applications. Other applications such as time delays, flux counters and transductors demanding extremely square hysteresis loops require selection of Square Orthonol.



I am not convinced that this is good material for current transformers. A small amount of dc current will cause the core to saturate.

The model matches the Magnetics Inc datasheet for the material.

I have used the Chan model for ferrite material and found it to be reliable.

Regards,
Jay_Diddy_B

uer166:

--- Quote from: Jay_Diddy_B on June 26, 2019, 02:28:42 am ---
I am not convinced that this is good material for current transformers. A small amount of dc current will cause the core to saturate.

--- End quote ---

It is not a current transformer, rather a DC current sensor based on a different effect. The mechanism relies on the core to be easily saturated, and it does so at some frequency in the "bistable switching devices" use case as postulated by manufacturer of the core.

Jay_Diddy_B:

--- Quote from: uer166 on June 26, 2019, 04:40:33 am ---
--- Quote from: Jay_Diddy_B on June 26, 2019, 02:28:42 am ---
I am not convinced that this is good material for current transformers. A small amount of dc current will cause the core to saturate.

--- End quote ---

It is not a current transformer, rather a DC current sensor based on a different effect. The mechanism relies on the core to be easily saturated, and it does so at some frequency in the "bistable switching devices" use case as postulated by manufacturer of the core.

--- End quote ---

Hi,

So you want to model a dc current sensor, similar to the one described here:

Link: https://www.nutsvolts.com/magazine/article/magnetic-saturation-and-the-100-amp-dc-current-transformer



I can modify the model, using the same core described in my earlier post, to include the DCCT functionality:



I am stepping the input current from -100A to 100A. The circuit works as described in the Nuts and Volts article.

The core is an oscillator, a low pass filter is needed to extract the average value.



I have attached the LTspice models.

Regards,

Jay_Diddy_B


uer166:
I think fundamentally the operation of that 100A coil is the same as in what I have in mind, except I'm trying to make use of the coercive magnetization to make a sort of "pseudo"-differential measurement of low current values (in order of a couple mA DC).

Basically go one way into saturation, then the other way, and see where the current hits the "wall" that coincides with the Hc point. This wall will move in opposite directions when there's another source of DC flux in the core, making measurement possible.

While simulation works great, while waiting for hardware, I'm trying to see all potential real world issues.

One thing I'm having a hard time reconciling is the ridiculous change of Hc (Coercive force) with frequency. (Example attached). This means that the location of the "HC wall" shifts with frequency, but I can't visualize how that looks like when one applies some field to the core.

What does this really mean? To me, the coercive force is just how much field you need to create in opposite direction to reset the magnetization of material once it hit saturation one way. Why would frequency affect that? Are they talking about a simple sinusoidal field? What happens if the field is close to a square wave? Does that mean the simulation is woefully incorrect since it implies a constant Hc, which is actually 10s or 100s of times higher at high frequency (e.g. at the square wave edges)?

This doesn't seem trivial, but I wonder if it's possible to simulate even more arbitrary cores where the BH curve itself shifts with frequency (becomes much wider at higher frequencies), as it does in real life.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod