Hello! My apologies if this is a stupid question, for I haven't been on this list or in the magnetics business for very long.
I am modeling a three-phase permanent magnet alternator for use in a small wind turbine. Of immediate interest is the cogging (detent) torque, which must be overcome for the machine to begin turning from a stop.
I have read the manual section on the torque integral, set up my air gap with at least four nodes between magnet and teeth, and the field solution that is generated looks qualitatively reasonable. But the values given by the torque integral around the bore are inconsistent. First of all, the sign of the value seems to switch randomly, perhaps because of some subtlety of how I highlight the curve.
Secondly, my method is to repetitively solve the geometry with the rotor rotated incrementally some increasing fraction of a tooth pitch. (If anyone knows a better method for cogging I would be thrilled to know it; could this be scripted with the "lua" business? I've been re-exporting the cad file and redefining everything for each increment.) I was expecting to see a smooth, roughly sinusoidal result of torque vs angle, but so far the data appear random, though the order of magnitude (~3Nm/m) is in good agreement with experimental results for peak cogging torque.
If anyone has tackled this problem I would be very thankful for advice.
Thanks,
Ben Polito