Driving IPM Motors Neglecting Reluctance?

Electric Motors and Controllers
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coleasterling
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Driving IPM Motors Neglecting Reluctance?

Post by coleasterling » Nov 16, 2017 11:27 am

Hey Guys,

I've got a few IPM motors from various hybrid projects laying around, but don't yet have a firm enough grasp on the control theory to build an inverter (Lebowski, Hubner, etc...) to drive them properly. Is it feasible to drive IPM's with our standard vehicle and ebike controllers, only taking into account the magnetic torque? I've read figures for reluctance torque to be from 10% to near 40% of a motor's overall torque production, so it is obvious I'd be giving up a significant amount of torque, but that's not too much of a concern at this time. I haven't tested yet, but I'm assuming that embedding halls in the stator won't work, so I'll need to either make an external magnet array with halls, or find an encoder to fit that outputs UVW.

Any thoughts?

Thanks!
Cole

coleasterling
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Re: Driving IPM Motors Neglecting Reluctance?

Post by coleasterling » Nov 20, 2017 2:13 pm

Update: Looks like it works just fine no-load on a couple HVH250's I have here, though I don't have any method of dynoing or loading them. My main question now is to find out what that does to efficiency.

coleasterling
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Re: Driving IPM Motors Neglecting Reluctance?

Post by coleasterling » Nov 22, 2017 12:39 pm

Bumping this one more time before giving up. Anyone tried this on a loaded motor?

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fechter
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Re: Driving IPM Motors Neglecting Reluctance?

Post by fechter » Nov 22, 2017 3:36 pm

I posted a few responses here while the board was getting reconfigured, so they got lost.
From what I can tell, you should be able to drive an IPM motor with a bike or RC controller but you might not be able to get the full rated power from it or the efficiency might go bad at high load. A sensorless controller might be the easiest. I suspect it will be pretty good up to about 80% power.

There are some sensorless control schemes made for IPM motors based on measuring the inductance at high frequency and deducing the rotor position from that. This doesn't really work so well for normal external magnet designs.
"One test is worth a thousand opinions"

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liveforphysics
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Re: Driving IPM Motors Neglecting Reluctance?

Post by liveforphysics » Nov 22, 2017 4:35 pm

It works to run them on just the PM field, just makes a reduced torque motor at low RPM, but it can still be very efficient.

As we saw Arlins leaf motor (IPM) dyno big HP and torque, and it run a lebowski brain to control it, I would simply use that brain and put your own effort into the power stage.
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fechter
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Re: Driving IPM Motors Neglecting Reluctance?

Post by fechter » Nov 22, 2017 6:05 pm

Ah, the expert!

Do you know what the Leaf motor uses for rotor position sensing?
"One test is worth a thousand opinions"

coleasterling
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Re: Driving IPM Motors Neglecting Reluctance?

Post by coleasterling » Nov 23, 2017 10:10 am

Thanks Fechter and Luke!

I thought Arlin had made changes to suit the IPM, no? In my understanding, you need to characterize the angle of the reluctance torque at many different commanded current values, since it changes with current? Something like that. Anyway, a lookup table was proposed, but I don't think it was implemented. It has been awhile since I went through that thread. I would assume the autotune in Lebowski's chip can only account for magnetic torque.

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