Chris Morriss Writes:
In PM-BLDC and (especially) switched reluctance motors, the real issue
is the magnetic losses due to the magnitude of the delta-B in the
stators and rotors......(snip)......means that the change of flux (delta-B) in the rotor backing material can be quite low......(snip).......need for thin laminations of electrical
steel.....snip......., either stamped or (for small quantities) cut by NC water-jet
machines."
"I would be interested in knowing what magnetic simulation software there is..."
Yes, I agree. The increasing need for low losses in cores (& way worse with high freq. switching) brings up the old problem of eddy currents and the traditional solution of using laminated cores to control eddy currents - laminations which you quite properly point out are difficult to cut to shape in close tolerance in a home workshop. There is also the problem that some of the best lamination material loses some of it's goodness when it is stressed. Unhappily that happens when high permeability steel is impacted, bent, or sheared mechanically. It probably applies to water jetting as well, although I have solved that in the past by simply burying my head in the sand.....there being no better way to make them.
Chris, I don't have a good solution for making core laminations. Wish I did. Stacking hand-cut laminations is a real pain. Even assembling them after having them water-jet cut is a pain.
Personally, I am hopeful that the solution for the home builder will be to print laminations in 3-D stereolithography. Sooner the better. Then we could experiment with laminations composed of closely packed particles - theoretically that would have advantages over today's contiguous quasi 2-D laminations.
A couple of years ago I did play with printing some coils and that did work - although the flux density wasn't high enough for a motor with high HP. Good enough for control circuitry however. ...
For the kind of dense coil needed for a powerful motor it's going to be hard to beat winding with modern "magnet wire". After all, wire-wound coils have already had about a century of dedicated development.
Of course all of those problems go away in a computer model. So we can always build one of those plus a prototype motor with a solid core and then wave our arms.
My favorite magnetic modeling program is FEMM by David Meeker. Simple to use and has a wonderful tutorial section.
Luck, Roger L.
for..... the design of salient-pole BLDC motors of the PM or
switched-reluctance type. There is free software for general ac and dc
magnetic simulation, but something specifically designed for motors
would be useful, provided the cost is not too high and it's easy to use!
My interest is for a low speed rim-drive thruster to propel a narrowboat
on a stretch of a preserved canal in the UK (see
www.cromfordcanal.info). The boat has to operate on a part of the canal
with many wildlife preservation orders, so pure electrical propulsion,
with a thruster that produces minimum tip-scour from the prop on the
silt bed of the canal is desirable.
A switched reluctance motor having no permanent magnets is desirable, as
a PM motor always has a strong magnetic field in the gap between the
stator and rotor, even when not running. The canal silt has a lot of
ferrous material in it which will quickly get trapped in this field on
the sort of rim-drive motor I envisage (outer stator, ring rotor, with a
4-blade prop fitting inside the ring). An S-R motor has no residual
field, but has the problem that the gap between the salient poles of the
rotor and stator has to be narrower than with a PM type to ensure a high
efficiency. Hence my interest in the simulation software.
Anyone else here have any working knowledge of rim-drive ring thrusters?
Thanks,
--
Chris Morriss
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