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Re: [FEMM] How to freeze the reluctivities in each element?

Ramdane LATEB wrote:

Hello, I'm simulating an induction machine under a non linear field solution with femm and through lua language, I need to calculate all parameters of the machine. The idea is to determine all the parameters of the equivalent circuit of a specific slip frequency. For this purpose I need to freeze the reluctivities of each element found from the latest non linear field solutions and perform a linear FE calculation at synchronous speed with slip=0 (for the details see Ping Zhou."Finite Element Analysis of Induction Motors Based on Computing Detailed Equivalent Circuit Parameters, IEEE Trans. On Magn. Vol. 34; N°.5., Sept 1998". The problem is that I don't know how to get the reluctivities of each element through lua (in femm).
Any idea is welcome

You currently can't directly access the arrays of data associated with the nodes and elements through lua. I'd been meaning to write some functions to allow this data to be accessible to Lua, but I haven't gotten around to it yet. Another difficulty would be that you can't specify material properties arbitrarily on an element-by-element basis without making some modifications to the way that the solver works.

At any rate, it seems like the approach described in the paper you referenced is pretty difficult. It seems like if you want to kludge the analysis of an induction machine with nonlinear materials using a model without motion (there's an example of a parameter identification approach applied to a machine with linear materials on the FEMM examples page), perhaps the easiest way to go about it would be to do a nonlinear time-harmonic analysis at the line frequency (i.e. 60 Hz or 50 Hz or whatever) with the conductivities of all materials in the rotor multiplied by the slip. This model would produce the "same" torque as the equivalent rotating machine under load; the rotor losses in the motionless model would equal the rotor losses + mechanical output of the rotating machine, and so on. By looking at stored energy, the phase and magnitude of the stored currents, the terminal voltage, etc., one ought to be able to back out some parameters for impedances that could yield equivalent behavior at that operating point. N.B.--if you use the latest-n-greatest 4.0 development version and define the windings using the new series-connected wound "circuits", the terminal voltage and flux linkage gets computed for you automatically.

Dave.

--
David Meeker
Senior Engineer
Foster-Miller, Inc.
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Waltham, MA 02451-1196
781-684-4070
781-890-3489 (fax)
dmeeker@xxxxxxxxxxxxxxxxx http://femm.foster-miller.com