Reluctance motors

[bobc]

Anybody looking at reluctance motors?
Switched reluctance have traditionally been popular in ecar research, (though nothing big commercially)
These should be the easiest (cheapest) motors to make - but they tend to be acoustically noisy because of the magnetic forces on the casing. Stepper motors (e.g. NEMA 17) are switched reluctance
Synchronous reluctance (unfortunately has the same acronym) have recently become popular in industrial drives as they can use a lot of the same tooling and inverter technology as (extremely popular/widespread) induction motors but with no slip, they achieve the now fashionable high efficiency classes that induction motors can't reach.
Synchronous reluctance would seem to have a lot going for it - good efficiency (the main thing,- allows the motor to be small), no use of fancy magnets; yet I never saw anything in the 'press' regarding e-vehicles or ebikes.
For a "tinkerer" in a shed, I'd expect switched reluctance to be a lot easier to make, mostly because of the highly salient stator structure. FWIW I made a synchronous reluctance motor at work a few years ago (before they became a commodity) by getting a sheet of non-directional magnetic steel laser cut (this was for work) and using an induction motor stator - worked pretty good...
Just pointing out that it's not as hard as you might think to actually make real prototypes.!
PS - just saw the thread title "Permanent Magnet....." sorry....

 

[Miles]

Hi Bob,

No problem. I've started a new topic.

There was a motorbike that used an SR motor. It's no longer made but I'll see if I can find a reference.

Edit
Here's the link: http://www.electricmotorbike.org/index.php?page=lectra

 

[spinningmagnets]

Miles, this sounds interesting, especially if neo magnet supply gets interrupted. Would a variable reluctance motor have less power potential per volume? I suspect it would have to be larger in order to have the same power as the type of non-hub motors we are used to these days. I am intrigued that the small example motorcycle used 24V (to get 45-mph), would a higher voltage have only a small improvement in torque? (And a higher response to more amps instead?)

 

[Miles]

Ron, nothing beats the continuous torque density of an SPM motor but, I think reluctance drives can achieve pretty good power to weight/volume as well as high efficiencies. I haven't really researched this area, though. One big advantage, of course, is virtually no parasitic drag.

 

[bobc]

Thought I'd list what I know about these things.
It won't take long....
For industry synchronous reluctance have become interesting for several reasons. The main one is that industry is now "used to" inverters. A synchronous motor won't work without an inverter & that used to frighten mechanical engineers. Also in EU energy efficiency legislation is on an upward trend, and you simply can't get an aluminium caged induction motor into IE3 never mind any putative IE4. The synchronous reluctance motor can fill that hole by replacing an induction motor squirrel cage rotor with a simple laminated rotor with flux barriers; the stator remains pretty much as it was.
This is the design I made for my rotor, it goes in a 1hp motor shell.

Lasering these laminations was £250 for 150 laminations. It was interesting to play with but we couldn't justify the time it would take to develop a practical control solution. We were able to run it open loop up to about 2/3 speed and 1/3 torque, enough to show it was ~10% more efficient than the squirrel cage rotor it replaced.
I know that siemens and ABB sell synchr. reluctance motor ranges from the catalog now, including control. This stuff is out there

To be frank, I don't think synchronous reluctance is all that interesting for ebikes. It's industry advantages (smooth torque, re-use of induction motor stators) are no benefit. Switched reluctance looks much more promising. Easy, cheap to make motors and easier control. PMSM will always have better power density and efficiency (because the magnetisation comes for free) but the SRM might end up nearly as small and nearly as efficient, but with a much cheaper motor.
Wish I knew anything to write about switched reluctance....

 

[atarijedi]

Thought I'd list what I know about these things.
It won't take long....
For industry synchronous reluctance have become interesting for several reasons. The main one is that industry is now "used to" inverters. A synchronous motor won't work without an inverter & that used to frighten mechanical engineers. Also in EU energy efficiency legislation is on an upward trend, and you simply can't get an aluminium caged induction motor into IE3 never mind any putative IE4. The synchronous reluctance motor can fill that hole by replacing an induction motor squirrel cage rotor with a simple laminated rotor with flux barriers; the stator remains pretty much as it was.
This is the design I made for my rotor, it goes in a 1hp motor shell.

Lasering these laminations was £250 for 150 laminations. It was interesting to play with but we couldn't justify the time it would take to develop a practical control solution. We were able to run it open loop up to about 2/3 speed and 1/3 torque, enough to show it was ~10% more efficient than the squirrel cage rotor it replaced.
I know that siemens and ABB sell synchr. reluctance motor ranges from the catalog now, including control. This stuff is out there

To be frank, I don't think synchronous reluctance is all that interesting for ebikes. It's industry advantages (smooth torque, re-use of induction motor stators) are no benefit. Switched reluctance looks much more promising. Easy, cheap to make motors and easier control. PMSM will always have better power density and efficiency (because the magnetisation comes for free) but the SRM might end up nearly as small and nearly as efficient, but with a much cheaper motor.
Wish I knew anything to write about switched reluctance....

I've been reading up on them. The biggest issue just seems to be finding someone who makes them in an appropriate size for an eBike.

This guy made his own motor just to see how it works, pretty neat > https://www.youtube.com/watch?v=W6LwlhsnT-k