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# Re: [femm] Inductance Calculation

- To: femm@yahoogroups.com
- Subject: Re: [femm] Inductance Calculation
- From: David Meeker <dmeeker@ieee.org>
- Date: Fri, 07 Mar 2003 09:37:48 -0500
- In-reply-to: <20030306135443.163.qmail@web41113.mail.yahoo.com>
- References: <20030306135443.163.qmail@web41113.mail.yahoo.com>
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`Tsarafidy RAMINOSOA wrote:`

> `
> Hello everybody,`

>     I would like to calculate the d and q inductance of a
>     synchronous machine. The relation Ld*Id^2 = Energy
>     (for a d axis field applied) is correct only for
>     linear case. But for saturated case, I'm a little
>     confused !
>     Any help would be very appreciated.

> `Best regards`
> `Tsarafidy.`

`There isn't such a clear interpretation of "inductance" for nonlinear systems, because inductance is a proportionality constant between current and flux linkage that is supposed to be independent of current. If you have a nonlinear system, you can get an inductance-like proportionality constant between the instantaneous current and the instantaneous flux via the A.J integral divided by i^2 (i.e. same procedure as with a linear system); however, this value is not related to energy in a simple way. Alternatively, if you have an AC system, it is sometimes useful to derive an "inductance" based on the average stored energy over a cycle that is a function of the current amplitude. In this case, you can pick the "inductance" so that the energy obeys linear-looking formulas for computing energy; however, there will be errors in the instantaneous flux density.`

    Dave.
    --
    David Meeker
    email: dmeeker@ieee.org
    www: http://femm.berlios.de/dmeeker

- References:
  - Inductance Calculation
    - From: Tsarafidy RAMINOSOA <tsarafidy@yahoo.fr>

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