Induction Motors ?

Electric Motors and Controllers
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qwerkus   1 kW

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Induction Motors ?

Post by qwerkus » Mar 28 2019 4:57pm

Hello,

I'm investigating the use of Induction dd hub motors, and would like to know more about the advantages and drawbacks vs PSMS motors. I found this paper quite intersting: https://pdfs.semanticscholar.org/bc07/e ... 0b70fa.pdf

Basically, the main drawback of direct drive hub motors are their narrow optimal efficiency spectrum. Each PSMS is designed to work at a given RPM, anything outside that range will significantly decrease efficiency, and hence lead to lower battery range. Just drive a DD motor uphill, and than a geared hub or a mid drive and you'll see for yourself.

One possibility would be to use an induction motor, and vary both magnetic fields according to usage. Strong overdrive a start for increased torque, and weak fields at high speed to decrease drag.

Of course induction motors come with a lot of drawbacks, like more weight (for the second coiling), overheating issues (because you pump power through 2x coils) and lower efficiency than PSMS (because you have to power 2x coils).

So the main question would be: would the increase in efficiency do to varying magnetic fields offset the drawbacks ?

KD5ZXG   10 W

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Re: Induction Motors ?

Post by KD5ZXG » Mar 28 2019 7:19pm

Once was a thing called "repulsion motor" that ran as a squirrel cage induction motor. But had liftable brushes for extra low speed torque and starting. I don't understand how it worked. Was good enough for trains...

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amberwolf   100 GW

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Re: Induction Motors ?

Post by amberwolf » Mar 28 2019 8:20pm

qwerkus wrote:
Mar 28 2019 4:57pm
One possibility would be to use an induction motor, and vary both magnetic fields according to usage.
Of course induction motors come with a lot of drawbacks, like more weight (for the second coiling), overheating issues (because you pump power through 2x coils) and lower efficiency than PSMS (because you have to power 2x coils).
I'm no motor expert...but AFAICR, induction motors only have one coil set; they induce a field with that into the rotor. So there isn't a second field you can vary.

There are "universal" brushed motors that have two coil sets, but they're used in series for universal motors (AC/DC), and they're not induction. Non-universal (DC-only) versions of them are sometimes used with the field separate from the rotor (armature), usually called Sepex.

Alternators may have two coil sets like that too.

I don't remember what other motors have separate (stator) field coils vs rotor/armature, but there probably are some. I just don't think they are induction motors.


Are you sure you're thinking of induction motors?

qwerkus   1 kW

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Re: Induction Motors ?

Post by qwerkus » Mar 29 2019 8:19pm

amberwolf wrote:
Mar 28 2019 8:20pm
qwerkus wrote:
Mar 28 2019 4:57pm
One possibility would be to use an induction motor, and vary both magnetic fields according to usage.
Of course induction motors come with a lot of drawbacks, like more weight (for the second coiling), overheating issues (because you pump power through 2x coils) and lower efficiency than PSMS (because you have to power 2x coils).
I'm no motor expert...but AFAICR, induction motors only have one coil set; they induce a field with that into the rotor. So there isn't a second field you can vary.

There are "universal" brushed motors that have two coil sets, but they're used in series for universal motors (AC/DC), and they're not induction. Non-universal (DC-only) versions of them are sometimes used with the field separate from the rotor (armature), usually called Sepex.

Alternators may have two coil sets like that too.

I don't remember what other motors have separate (stator) field coils vs rotor/armature, but there probably are some. I just don't think they are induction motors.


Are you sure you're thinking of induction motors?
Well the guy calls it IM for induction motor, and i think he is right. Any electrical motor needs 2 magnetic fields to work. As long as you use copper coils on both rotor and stator, instead of magnets on one side, it s call an induction motor, because the resistive field is induced. Read the paper: although it focuses on servo motors, his bottom line is that over a wide range of speed, infuction motor with controlled field weakening can be of smaller size for the same torque output. The main issue with induction motors is overdrive, which quickly leads to high temps, while it is much more forgiving in psms motor. That s why a dd hub can actually start... solution is good thermal management and controlled flux gap according to the paper. That ebike motors need a speed range that justifes the use of IM is what i m researching now. After all, dd hubs operate between 0 and a few hundred rpm - thats far from the 10 000rpm of industrial servo motors.

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