# whats the difference between permanent magnet and induction motors



## few2many (Jun 23, 2009)

I know the main difference is of course the magnets, but are the windings and poles really any different?
could the same controller running a 3 phase induction motor run a 3 phase motor with permanent mags in the rotor?


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## major (Apr 4, 2008)

few2many said:


> I know the main difference is of course the magnets, but are the windings and poles really any different?
> could the same controller running a 3 phase induction motor run a 3 phase motor with permanent mags in the rotor?


Some controllers can. But usually it takes position as well as velocity feedback for PM motors and a change in the control software.

major


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## few2many (Jun 23, 2009)

Is it more efficient to have permanent magnets in the rotor? Instead of having to waste power to induce the mag field, its already there, and any regen would be higher?


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## major (Apr 4, 2008)

Hi few2,



few2many said:


> Is it more efficient to have permanent magnets in the rotor?


Depends on the loading of the motor and the duty cycle. Peak efficiency on the PM would likely be higher than peak efficiency on the ACIM, but EV motors don't operate at a single point load. 



> ......... and any regen would be higher?


If properly controlled, regeneration capability should be about the same. I might tend to give the edge to the ACIM because it is easier to field weaken, but this is highly dependent on the application.

Regards,

major


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## yarross (Jan 7, 2009)

few2many said:


> I know the main difference is of course the magnets, but are the windings and poles really any different?


Both have stators that are pretty similar, at least for high speed machines.



major said:


> Depends on the loading of the motor and the duty cycle. Peak efficiency on the PM would likely be higher than peak efficiency on the ACIM, but EV motors don't operate at a single point load.


 At partial loads, PMs are noticeably more efficient - typically. By giving away with the paradigm of keeping full excitation at partial loads, ACIMs losses can be somewhat decreased, improving partial load efficiency. I do believe Tesla roadsters make use of this approach.


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## few2many (Jun 23, 2009)

Yeah, I asked because the new Focus EV and some other EV's are running the permag motors. (yeah, made up word permag. if you got it you have the right mindset, scary)


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