12 phase motor for high storque/ power density

[Learn2Live]

For greater torque/ power density in an electric motor, can four 3 phase field magnet systems be integrated together into a single "12 phase" field magnet system by running all 3 phase systems together but with each 3 phase system leading by 90 electrical degrees before the one behind it and lagging 90 electrical degrees behind the one leading it? Can this be accomplished inexpensively without inverters? In what ways can power phases be delayed or moved ahead by the said 90 electrical degrees?

 

[MacGyverS2000]

There are plenty of n-pole motors out there (where 'n' is as large as you can practically imagine), so the overall concept of a 12-pole motor is useable. They're typically run by a solid-state, multi-phase controller, though I see no issue with running that as 4 separate systems (with reduced efficiency and functionality).

Perhaps others with more motor experience will kick in here...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[onatirec]

As far as I'm aware, a 12 phase motor is feasible. We make 3-phase pmsms here, but my understanding is you'll likely find diminishing returns with a higher number of phases (above 3-4) due to increased conductor sizing to achieve the same power. Practically speaking, in a 12 phase motor you'd have 6 sets of anti-parallel phases so the machine would be reducible to a duplex 6-phase supply. There could be a good reason to make such a motor; maybe to split up the supply of a large motor to make it more manageable or better fault tolerance. I'm not sure. This sort of machine falls into what's called a multiplex winding.

The poles don't quite correlate to the phase count - beyond a few rules for having a balanced motor, etc - e.g. you could easily produce a 44 pole motor to run off of 3-phase ac, though you're going to run into other limiting factors with a high rotor pole count such as magnetic saturation.

I'm certainly not an expert on motors - and even less so on control electronics. Simple circuits tell me that capacitors and inductors would shift the electrical phase - though this also effectively be filtering your current. I'm not sure of the best way to condition such an input - it would also depend on the back-emf waveform. At the end of the day there's no free lunch.

As for the torque/power density, you're going to eventually run into upper limits on both the electrical and magnetic side. Both are temperature limited and have losses that would need to be taken into account.

 

[waross]

Did you mean "Poles" rather than "Phases"
Three phase power is readily available from the grid.
A Variable Frequency Drive will synthesize three phase power at a varying frequency and voltage from a three phase source, (The most common.)
Some will a synthesize three phase power at a varying frequency and voltage from a single phase source,
Some will a synthesize three phase power at a varying frequency and voltage from a DC source.
Three phase is easy, twelve phase, not so much.
Running on easily available three phase, the minimum number of pairs is one. It will work but the efficiency will suck.
The minimum reasonable number of pole pairs is three. You may increase the number of poles in multiples of three.
But really, spend a little time studying motor theory before trying to re-invent the wheel.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Learn2Live]

Thanks for your replies, gentlemen. I meant 12 phase. As far as I understand (if you could say I do), a 12 phase motor could be powered by triple or even single phase, if a special VFD consisting of a sufficiently sized AC-DC converter and sufficient DC-AC inverters which in turn would change the converter's DC output back into AC, producing all phases of the AC power to run said motor. In terms of doability, whether it is three phase or single phase fed would not matter since it would first be converted to DC in the VFD anyway. I imagine this in an axial flux pancake motor configuration. I am almost excited just thinking how smaller motors could get.

 

[Learn2Live]

I've a 72 slot (12ph, 6p) stator practice sketch on my 4MCAD 21 Pro. At least how I envision an axial flux pancake motor stator could look like. I still have to learn more about VFD's. I still wonder how the rotor would look for this to be a synRM. Higher power density would be good for MRL applications, don't you think? Lower traction motor weight and smaller footprint.