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Home / Technical Notes / Magnetic analysis / Inductance Calculation Type
Inductance Calculation Type
If permeability of magnetic material is defined nonlinearly (or if the magnetization type is set to B-H curve on the [Permeability tab]),
inductance changes depending on the current magnitude.
There are two definitions of inductance as follows.
1. Apparent Inductance
It is expressed as follow where Φ is interlinkage magnetic flux and I is current.
L=Φ/I
2. Differential Inductance
It is expressed as follow where Φ is interlinkage magnetic flux and I is current.
L=dΦ/dI
In the below graph of current and interlinkage magnetic flux, a black circle is a working point.
A dotted line 1 represents apparent Inductance Φ/I.
A dotted line 2 represents differential inductance dΦ/dI.
Calculation Type of Femtet
Calculation types for each analysis are listed below.
Generally, the differential inductance is used for the superimposed DC characteristic analysis.
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Analysis Type |
Material with |
Inductance Calculation Type |
Notes |
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Static Analysis |
Linear permeability |
--- |
Both calculation types will give the same value with the linear permeability. |
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Nonlinear permeability (B-H curve) |
Select either apparent inductance or differential inductance in the analysis condition settings. |
--- |
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Minor-loop permeability (Superimposed DC characteristic analysis) |
Fixed with differential inductance |
The minor-loop differential permeability is used. |
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Harmonic Analysis |
Linear permeability |
--- |
Both calculation types will give the same value with the linear permeability. |
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Minor-loop permeability (Superimposed DC characteristic analysis) |
Fixed with differential inductance |
The minor-loop differential permeability is used. |
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Transient Analysis |
Linear permeability |
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Both calculation types will give the same value with the linear permeability. |
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Nonlinear permeability (B-H curve) |
Fixed with apparent inductance |
With the current I and apparent inductance L of two timesteps,
Differential inductance=(L2-L1)/(I2-I1)
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Apparent Permeability and Differential Permeability
In the B-H curve below, a black circle is a working point.
A dotted line 1 represents apparent permeability: B/H
A dotted line 2 represents differential permeability: dB/dH
