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# Re: [femm] SRM Modeling

- To: femm@yahoogroups.com
- Subject: Re: [femm] SRM Modeling
- From: David Meeker <dmeeker@ieee.org>
- Date: Wed, 27 Nov 2002 01:00:52 -0500
- References: <000001c292b9$aa2bafb0$cbea7481@robotics1rkby4>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.1) Gecko/20020826

`Pradeepkumar Ashok wrote:`

> `Hi all,`

>     Has anyone used FEMM to model and evaluate the torque capacity of a
>     switched reluctance motor? I need help

>     My FEM model only gives me half the torque that my analytical
>     calculations predict. For those interested, the plots and the machine
>     dimensions are in the file called comparisons.doc . The analytical
>     method I used was based on a paper by Radun Analytically Computing the
>     Flux linked by a Switched reluctance motor phase when the stator and
>     rotor pole overlap. This paper uses the magnetic co-energy method to
>     calculate torque, while FEMM uses the stress tensor method. Could that
>     be a reason for the difference? I dont think so&but I am not sure&

>     In the models, I used triangle to mesh the air gap between the stator
>     and the rotor poles (remodel.fem) . I also used a slightly different
>     model with a finer mesh (.0005) between the stator and rotor poles
>     (remodel2.fem) to see if this problem was due to my mesh being coarse.
>     The airgap is .0125 inch and so I felt that .0005 was more than
>     sufficient. I found the torque output from these two cases to be not too
>     different. So I went ahead a created a Lua script to plot the static
>     torque Vs Rotor position Vs Current. (Files inside the folder
>     torque_sim),and that is how I got the plot shown in comparisons.doc

>     Simply put my question is Have I modeled the machine correctly& If so,
>     I can safely attribute this difference to errors in the analytical
>     model. Can somebody help ?

`
I didn't run the script all the way through, but there were a few of things that I noticed:`
`-- Your script only changes the current density in the Imax material. I think that you also need to change the Imin material in an analogous way to get correct results.`
`-- It's best to draw the contour along which the stress tensor is taken through the center of the air gap, rather than to one side.`
`-- Make the arcs that compose the pole faces and integration contour have a finer discretization (like 1 degree or less). This will get rid of the cogging in your graphs of torque versus rotational position.`
`Dave.`

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

``

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- References:
  - SRM Modeling
    - From: "Pradeepkumar Ashok" <pradeepkumar@mail.utexas.edu>

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