Dual rotor axial flux motor design

Electric Motors and Controllers

Re: Dual rotor axial flux motor design

Postby kenkad » Sat Mar 17, 2012 10:51 am

fechter,
Your comment about the tooth offset for single direction rotation is interesting. Some two years ago, I had asked Shane Colton (when he was deep into dual rotor axial flux design) about this type of thing and if a better solution might be to 'skew' the offset of the dual rotors a small amount (maybe somehere between 1-3 degrees). He was going to try that to see if it also minimized cogging, but, I do not think it finally worked into his efforts. At least he never indicated that there was any noticable effect. I personally believe that it would be more noticable as a minimization of cogging. Since I am not a motor designer, this may be way off base. This is on my list (rotor skewing) of things I want to test as well as magnet orientation of the adjacent magnets on the rotor (not the typical N/S in/out orientation). Isn't learning fun?
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Re: Dual rotor axial flux motor design

Postby Kingfish » Sat Mar 17, 2012 12:35 pm

Some months back someone posted an induction motor that had renderings, photos, or animations of a C-shaped (as opposed to skewed) laminated stator by some big-named company (possibly GM or Honda). The stator had big single-copper wire turns. My understanding was the skewing and C-shape is designed to reduce torque ripple, although I find the affect upon saturation interesting and appealing. Unfortunately most of us do not have advanced-level modeling software and full-time researchers figuring out the proper mechanical offsets per each lamination.

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Re: Dual rotor axial flux motor design

Postby Miles » Sat Mar 17, 2012 1:10 pm

Just looking at the Sineton dual stator radial design (below, top left):
http://www.sineton.com/web/index-10.html
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Re: Dual rotor axial flux motor design

Postby Miles » Sat Mar 17, 2012 1:35 pm

N.B.
"Core losses are substantially reduced with the use of a grain oriented silicon steel."
http://www.sineton.com/web/index-33.html

It's not clear how they take advantage of GO steel with the above topology...
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Re: Dual rotor axial flux motor design

Postby Miles » Wed Mar 21, 2012 5:35 am

Latest version:
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Re: Dual rotor axial flux motor design

Postby Miles » Wed Mar 21, 2012 5:41 am

OD increased from 92mm to 100mm
Electrical loading increased. Rm is now circa 4 milliohms.
Kv <150 rpm/V
Nominal speed 4000rpm
Flux frequency at nominal speed 533 Hz
Core volume 8.5222E4 cubic mm
Core mass 0.672 kg
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Re: Dual rotor axial flux motor design

Postby fechter » Wed Mar 21, 2012 8:12 am

You might need some kind of housing to connect the two end plates together. Lamination stacks are not very rigid. There could be some eddy currents in the screws holding the lams together, but it should be fairly minimal. Normally they try to avoid having the fasteners in the teeth. It would be a lot of work, but it might be worth using some kind of adhesive between the laminations.
"One test is worth a thousand opinions"
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Re: Dual rotor axial flux motor design

Postby Miles » Wed Mar 21, 2012 8:41 am

fechter wrote:It would be a lot of work, but it might be worth using some kind of adhesive between the laminations.
I definitely want to bond the laminations together. At the moment, the plan is to get the 75+ different lamination profiles laser cut and bonded into core modules. Haven't had a quote yet, though :mrgreen:
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Re: Dual rotor axial flux motor design

Postby Miles » Wed Mar 21, 2012 9:07 am

Can I get a very rough approximation of the iron losses from the Watts per lb value given in the electrical steel specifications?

For Arnolds thin gauge GO 6mil (0.15mm) @ 15kG (1.5T); 400 Hz the losses are 9 Watts per lb.

My core weighs 1.48lbs. So, that's 13.5 Watts @ 1.5T; 400 Hz.

Say, 21 Watts at 533 Hz 1.5T.

Increase that to 25 Watts to allow for the greater flux density.

Increase again to 30 Watts to allow for stray, windage and bearing losses...
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Re: Dual rotor axial flux motor design

Postby Miles » Wed Mar 21, 2012 9:40 am

This is what the above figures look like in Drive Calc...... :shock:
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Re: Dual rotor axial flux motor design

Postby Miles » Wed Mar 21, 2012 2:58 pm

Couldn't resist... :)

Looks a bit "steampunk"
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Re: Dual rotor axial flux motor design

Postby fechter » Wed Mar 21, 2012 9:49 pm

If the efficiency comes even close to the simulation it will be awesome. Most of us are dealing with 80% max.
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Re: Dual rotor axial flux motor design

Postby markobetti » Thu Mar 22, 2012 5:00 am

Miles wrote:Couldn't resist... :)

Looks a bit "steampunk"



i love it . Its going to make a beautiful BUH motor . By the way we have LAH 00000009 on board :)
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Re: Dual rotor axial flux motor design

Postby Doctor » Fri Mar 30, 2012 12:35 am

HI all,
Maybe I am wrong, but to me it looks like the laminate direction in this design is wrong: look at the Apex drive lab's stator pictures ( http://www.apexdrivelabs.com/brushless- ... mages.html ), each ply of the laminate is oriented in radial direction.
On other hand I know that in other types of axial flux machines (for instance, in Thorus topology) the laminate oriented perpendicularly to the radial direction. Why is it so?
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Re: Dual rotor axial flux motor design

Postby Miles » Fri Mar 30, 2012 1:43 am

Welcome Doc!

This is the orientation that corresponds to the lamination direction in a radial flux motor. Most axial flux motors have laminations running circumferentially (spiral wound). In the Schiller design, which has a segmented stator, the laminations run this way. AFAIK, it is the optimum orientation for the containment of eddy currents.

Surely the apparent twin cores in the Apex design must be contiguous (a "U" shape)? So, in their case, the laminate direction would be a compromise to achieve the topology.

Other motors (eg Lynch) have the laminations running radially, so it can't be too much of a compromise.

I'd like to know more about this, too!
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Re: Dual rotor axial flux motor design

Postby Miles » Fri Mar 30, 2012 2:42 am

This is interesting...
http://www.set.ugent.be/docs/TO_HEAF_v2.pdf

That makes 3 ways to equalise the radial flux density:

- Equalise, per lamination, the ratio of the cross sections of the core "head" to core "neck" .

- Reduce magnet area as radius decreases (only applicable in the case where the no. of poles is less than no.of slots).

- Reduce the airgap distance as radius increases (Ghent university proposal).
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Re: Dual rotor axial flux motor design

Postby Miles » Fri Mar 30, 2012 5:14 am

Axial-flux permanent-magnet machine modeling, design, simulation and analysis.
A. Mahmoudi*, N. A. Rahim and W. P. Hew
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Re: Dual rotor axial flux motor design

Postby Miles » Fri Mar 30, 2012 6:37 am

Adopting the US vernacular....: Woot! :D

Comparison of Nonoriented and Grain-Oriented Material in an Axial Flux
Permanent-Magnet Machine

Damian Kowal, Peter Sergeant, Luc Dupré, and Alex Van den Bossche

V. CONCLUSION
For an AFPMSM whose stator flux is flowing in axial direction
in the major part of the stator, GO material was compared
with NO material. With GO material, the machine has about 7
times less iron loss at the same speed, and a 10% higher torque
for the same current. Nevertheless, the EMF at no-load is almost
the same for both materials. For a given torque, the GO material
causes a 10% higher torque-to-current ratio which makes
it possible to reduce the copper losses—quadratic with the current—
by about 20%. Alternatively, because of the lower iron
losses, it is possible with GO material to allow larger copper
losses without increasing the temperature of the machine. This
means a higher stator current and more torque.We conclude that
for the considered type of PMSM, it is worth the extra cost to
use GO material.
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Re: Dual rotor axial flux motor design

Postby Miles » Fri Mar 30, 2012 7:06 am

Optimized Design Considering the Mass Influence of an Axial
Flux Permanent-Magnet Synchronous Generator
With Concentrated Pole Windings

Hendrik Vansompel, Peter Sergeant and Luc Dupré
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Re: Dual rotor axial flux motor design

Postby bearing » Fri Mar 30, 2012 7:45 am

Very nice finds!

Considering the amount of academic research done on axial flux motors, and the obvious advantages they have, I'm a bit confused to why there are so few axial flux motors available/produced/used commercially.
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Re: Dual rotor axial flux motor design

Postby kenkad » Fri Mar 30, 2012 8:14 am

Miles,
The end of the third paragraph on the Ghent papers says:
"contentrated pole windings----A disadvantage is that for a three-phase machine several windings should be connected in series. When connecting n concentrated windings in series, the total electromotive force is not n times the voltage of a single winding, because of phase shift in the neighboring windings. An atlternative is to make a machine with many phases [3]."

This is what I had tried to bring up earlier. I had see this paper before but had not copied it at that time. Thank you for posting it here so now I can make a copy and give it to the PhD student that hopefully will do my modeling/simulation soon. I believe that a nine phase motor cited in the reference above is bsically the same as three separate three-phase windings. I do know in my design that it reduces the required drive of each three-phase group.
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Re: Dual rotor axial flux motor design

Postby bearing » Fri Mar 30, 2012 8:28 am

When connecting n concentrated windings in series, the total electromotive force is not n times the voltage of a single winding, because of phase shift in the neighboring windings


This is the so called "winding factor". In a good design the phase difference won't be very big. I think Miles had about 0.95, so it won't do much to increase it to 1.
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Re: Dual rotor axial flux motor design

Postby Miles » Fri Mar 30, 2012 8:30 am

Have you seen this one, Ken?
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Re: Dual rotor axial flux motor design

Postby Miles » Fri Mar 30, 2012 8:32 am

bearing wrote:
When connecting n concentrated windings in series, the total electromotive force is not n times the voltage of a single winding, because of phase shift in the neighboring windings


This is the so called "winding factor". In a good design the phase difference won't be very big. I think Miles had about 0.95, so it won't do much to increase it to 1.

As they say:
Although a multiphase system for concentrated pole windings
is proposed in [5], a regular three-phase system is used in
this paper. In order to obtain a high winding factor, the number
of teeth is set to 15 resulting in a winding factor of 0.951 for the
16-pole machine
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Re: Dual rotor axial flux motor design

Postby kenkad » Fri Mar 30, 2012 8:39 am

Miles,
Yes, I had this copy. This is a paper that the PhD students Professor cited to me as a probable issue of the harmonics. Of course, that is something to find out. I am not a motor designer as you and I have discussed before. There are a lot of tradeoffs in any design problem. I was trying to find a way create a motor design that would allow shutting down of some of the three-phase groups when a vehicle is crusing. At that point, cogging effects as less of an issue, etc. Sort of like running an 8-cyl engine on 4 cylinders to save fuel. It really makes a difference in finding a full bridge driver for each three-phase group! As usual, it will all come out in the end one way or another. If the simulation is of any consequence, then we go on to a prototype, if I live long enough or if we live through Dec 21, 2012 (ha ha).
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