Switched Reluctance - Ideal for DD Hubs?

Electric Motors and Controllers

Switched Reluctance - Ideal for DD Hubs?

Postby Username1 » Wed Mar 29, 2017 1:22 pm

I have been learning about various kinds of motors including switched reluctance. It seems like they could make the ideal direct drive hub motor...

Their advantages over pm motors include:
- 0 drag when off/coasting
- high efficiency over a much broader speed range (great for low rpm)
- no magnets to overheat
- motor itself is extremely simple and cheap to construct (controller excluded)

Downsides include:
- noisy (not sure if this can be fixed or not)
- needs sophisticated controller (doesn't pm also need this?)
- possibly a little lower torque (altough maybe in low speed high torque dd scenarios this wouldn't apply)

Why aren't these being sold for ebikes etc. or why hasn't someone attempted to build one? What's your opinion on this kind of motor used for dd hubs?
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby amberwolf » Wed Mar 29, 2017 2:50 pm

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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Username1 » Wed Mar 29, 2017 4:22 pm

Thanks I've search the website already and read most of these. I didn't seem to find a good explanation for why they aren't made, and just wanted some more opinions on their potential as dd hub motors.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Voltron » Wed Mar 29, 2017 7:01 pm

There were a couple of e-motorcycles that like the Lectra 24 that used frame mount reluctance motors ... But I think modern pm motors have a big enough edge in power density that reluctance can't compete, esp in a hub motor where there's a limited physical size it can be? And most of the people that use a powerful DD hub are usually on the throttle a lot,, so the cogging isn't usually an issue unless you have to pedal home....
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby amberwolf » Thu Mar 30, 2017 1:55 am

Another thread with a bit more info (some indirectly)

viewtopic.php?f=30&t=17652&hilit=reluctance+hub+motor
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby MurmurTech » Wed May 10, 2017 6:20 pm

Hello friend, I try to do dd hub srm. Wait another week. Let's see the result. The fastest news on YouTube SRMotor .
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby amberwolf » Thu May 11, 2017 1:29 am

That's pretty cool.

Make sure to post any sales or advertising stuff about it or your company *only* in the Online Market section, though.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby MurmurTech » Thu May 11, 2017 4:40 am

Thank you. This is not advertising)) do it yourself. I do not have a company yet. I want in the future. Now a home developer.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Lebowski » Thu May 11, 2017 4:42 am

would be a fun project to build a proper sensorless controller for that :D
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Harold in CR » Thu May 11, 2017 6:21 am

Would this possibly be an induction SW motor ? Where would one get the programmed/programmable chip ? Lebowski perhaps ? I for one would love to get this particular chip/board.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Lebowski » Thu May 11, 2017 6:38 am

Harold in CR wrote:Would this possibly be an induction SW motor ? Where would one get the programmed/programmable chip ? Lebowski perhaps ? I for one would love to get this particular chip/board.

as far as I understood this is a switched reluctance motor. It works by electromagets on the stator attracting the iron teeth on the rotor. There is no induction of current in the rotor.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby liveforphysics » Thu May 11, 2017 7:14 am

All EVs will be SR motors as controller tech improves.

Exciting to a a short flux path SR hubmotor! Awesome work Murmurtech!
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby bobc » Thu May 11, 2017 7:34 am

That's a proper job for home- made...... respect!
Luke, do you mean switched reluctance or synchronous reluctance? always a bit concerned about audio noise from switched reluctance, can only really be avoided by massive strength (weight).
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Lebowski » Thu May 11, 2017 8:47 am

liveforphysics wrote:All EVs will be SR motors as controller tech improves.


I once had a back-of-a-napkin look and got the feeling SR motors are not so difficult to control... the controller IC should be able to run one sensorless but only if you keep the throttle open... will need some adaptation to keep sync for no throttle, but otherwise SR motors are not that different from BLDC.... for my controller algo that is.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby bobc » Thu May 11, 2017 9:17 am

My (2nd hand) impression is that the sensorless operation has to keep track of the varying (position dependent) leakage inductance to derive rotor position & that it ends up quite a bit different to BLDC...
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Lebowski » Thu May 11, 2017 9:24 am

bobc wrote:My (2nd hand) impression is that the sensorless operation has to keep track of the varying (position dependent) leakage inductance to derive rotor position & that it ends up quite a bit different to BLDC...

We, Sir, disagree :wink:
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby MurmurTech » Thu May 11, 2017 9:42 am

In direct drive it will be difficult to be a sensorless. We are trying to do a non-point-to-point measuring the rate of current build-up, and comparing with the tabular value, calculating lags or outstrips. But it does not work well at the start. No problem optical encoder or resolver.

Also I have a 4 phase motor.
2 current limiters 1 and 3, 2 and 4 phases.
Control the current limit level. PWM 100%
The power bridges are completely independent for each phase with an optical isolation.

The motor continues to operate even if 2 windings or 2 power units are out of order. And 4 optical sensors also reserve each other. You can continue to move even 1 sensor, but if you push a little.

There is a dynamic regeneration mode adjustable from the brake handle, and a dynamic brake mode in the extreme position of the brake handles.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby bobc » Thu May 11, 2017 11:38 am

MMtech - I guess you're not using usual "totem pole" output bridges?
Also synchronous reluctance want sine excitation & traditional full bridge, but switched reluctance - sort of - don't.... These are different beasts, you're not mixing 'em up are you Bas?
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Lebowski » Thu May 11, 2017 11:50 am

Well, if anyone has a 3 phase SR motor I can borrow I'd be happy to try and build code for it :D
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby bobc » Thu May 11, 2017 11:53 am

Would you believe I made one (a synchronous reluctance machine) out of a small induction machine.... I'll see if I could "liberate" it from work.......
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Harold in CR » Thu May 11, 2017 1:36 pm

I am trying to build a controller (s) for an alternator/motor that is used to boost acceleration of a 2 litre gasoline engine across intersections or up steep hills. It is called a BAS e/assist motor. I know of someone that has one in Spain, but, not sure if he would loan it out. I could ask him.

Possibly Lebowski, you might check youtube on the 2012 and up model BAS and if you think it's possible, I will ask him
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby Lebowski » Thu May 11, 2017 1:54 pm

bobc wrote:Would you believe I made one (a synchronous reluctance machine) out of a small induction machine.... I'll see if I could "liberate" it from work.......

What is the difference between synchronous reluctance and switched reluctance ? Isn't it the same thing ?
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby liveforphysics » Thu May 11, 2017 1:56 pm

bobc wrote:Would you believe I made one (a synchronous reluctance machine) out of a small induction machine.... I'll see if I could "liberate" it from work.......


You may find if the induction machine was well designed, it makes a terrible stator to use for SR. This is because if the tooth head worked well for induction or PM, it's setup to guide the change in flux to ramp sinus (or at least smooth-ish). As the torque in SR depends on how dramatic the change in flux gets, they generally require straight stator teeth with no hammer-head tip for good SR performance (as you see in this gentleman's motor above).

Something else very slick you mentioned about the rotor mass issue is the SFP (short flux path) design rotors can just use little "U" shaped segments of steel to link flux just as far as it needs from tooth head to tooth head VS a huge lump hub of rotor iron and the flux path always crossing through the center of the big lump like you see in stepper motors etc.

SR controllers don't need full-bridges on phase legs, which is great for avoiding shoot-through drama on controller development. It also reduces hysteresis in the iron loss from the field always being in the same direction rather than flip flopping.

With only 3 phases they often have a LOT of torque ripple when you make them high specific torque density, but more-so than any other motor SR lends itself towards going poly-phase way beyond 3p, as each phase in the controller doesn't need to be anything more than a single switch/FET if you have a common star termination for all the phases at the motor.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby macribs » Thu May 11, 2017 2:22 pm

This I got to keep an eye on.
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Re: Switched Reluctance - Ideal for DD Hubs?

Postby bobc » Thu May 11, 2017 2:29 pm

Lebowski wrote:
bobc wrote:Would you believe I made one (a synchronous reluctance machine) out of a small induction machine.... I'll see if I could "liberate" it from work.......

What is the difference between synchronous reluctance and switched reluctance ? Isn't it the same thing ?

Nah , the only thing they really share is the acronym unfortunately. Synchronous reluctance is a smooth airgap machine (like the IM) whereas the switched reluctance is doubly salient. I'm supposing that's what LPF is talking about above. Both ABB and Siemens sell ranges of synchr reluctance machines for industry for the last few years (which is why I was interested & had to make my own before they became commercially available). They are intermediate between IM and BLDC/PSM in efficiency but should be cheaper than IM to make, which is why we were interested, obviously my old prototype hasn't been touched for a few years now 'proper' ones are around. If wikipedia doesn't have the info, the siemens and ABB websites will be loaded with this stuff because it fills the hole in EFF3 class and above in the low kilowatt region.
MMtech's thing above is classic switched reluctance, a synchronous reluctance rotor is not really suitable for an "outrunner", it's rotor is a round lamination stack with "flux guides" (curved slots) in to make it try to line up with the rotating MMF supplied by the stator. Totally wants sinusoidal drive and should be as smooth and quiet as an AIM.
They look as though you should be able to run them open loop with an induction motor drive, but I've tried & they get unstable when given serious load or speed.
A web search should quickly find some pictures
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