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I am trying to make current dependent inductor in LTspice according my mesurements. LTspice includes feature flux where "x" is referred to inductor's current but when I used it in combination with my measured results flux=(2E-11*x*x - 3E-09*x + 1E-06)*x it does not work and gives me wrong value. Measured current reffers to value L=1uH but it should be L=1.19uH. Can anyone help me with this problem or give me any advice how to make current dependant inductor which will be represanting my measurements? If you need any further info please ask. Thank you very much in advance for your help.printscreen of LTspice

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The x signifies the derivative, so you have to integrate your expression, first, in order to obtain it correctly.

For your case:

\$f(x)=2*10^{-11}*x^2-3*10^{-9}*x+10^{-6}\$

\$\int{f(x)}{dx}=6.666*10^{-12}*x^3-1.5*10^{-9}*x^2+10^{-6}*x\$

To verify the inductance, you can use a unity ramp current source, which will give a voltage proportional to its inductance:

verification

Notes (in case you want to try it out yourself):

  • Since your function varies slowly, I chose an interval of 200s to show its variation which, given the great dynamic range difference between the function's values and the time range, LTspice, by default, can show misleading results, so I disabled the waveform compression (imposing a small enough timestep would also have been enough).

  • There is a sharp rise right at the beginning. That is due to the derivative, I'm afraid it "comes with the territory".

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