Inductance and mutul inductance caculation

[stsc_sh@xxxxxxxx]

Before you caculate inductance or mutul inductance, you have to 
formulate your problem in such a way that all the currents (space, 
surface or linearly distributed) but one are set to zero. There must 
be no permanent magnets in your model. In that case equation above 
becomes xtremely simple and you can get inductance value as :
E
L = 2 * -----
I^2
where E is stored magnetic energy and I is the only current(amp-
turns). This question is used for selfinductance caculation. It's 
more exact than flux linkage caculation.

Also, you can get mutul inductance use flux linkage method by the 
below equation:

¦Õ
L = ----
I
where ¦Õ is the flux linkage with the coil excited by current I(amp-
turns). 

for plannar problem:

¡ÒA ¡¤dS ¡ÒA ¡¤dS
¦Õ = RightSide(--------- ) - LeftSide(---------)
¡ÒdS ¡ÒdS

where A is the vector magnetic potential; RightSide and LeftSide 
denote the right and the left side of the coil accordingly.

The difficult to use this equation is that we can't get dS from femm. 
But if we choose a uniform mesh density in coil cross section and the 
mesh is dense enough, we can assume that each dS is a constant in the 
cross section. So the equation become easy to caculate by femm:

¦Õ = RightSide( ¡ÒA ) - LeftSide( ¡ÒA )

Hope this can help you.

si hang