AC induction motor

Discussions regarding the Field Oriented Control (FOC) implementation on the VESC.
evjim
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Joined: 27 Jul 2017, 03:03
Location: MT

AC induction motor

Postby evjim » 27 Jul 2017, 03:06

Hi, can the foc mode be used with an ac induction moter in sensorless control or is the bemf totally different?

Also, I wish to adapt the controller to 1s, wondering if anyone has looked into this before?

Thanks

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: AC induction motor

Postby rew » 27 Jul 2017, 04:52

As far as I know, controlling an AC induction motor is slightly different but should be possible with the same hardware. But nobody has written the software yet.

The system depends on being able to stepdown the motor voltage to 12V, and 5V and from there to 3.3V. I've asked TI if I can supply the 12V externally, but they said: maybe, but the datasheet says not to do it, so don't. So the VESC design is quite fundamentally not able to run on voltages below 12V. Depending on the dropout in the 12V regulator which I don't know by heart and the UVLO threshold, it might work down to 10V or so.

In my design, I could leave out the 12V and 5V stepdown converters (on the PCB). and substitute step-up converters externally. Then it could work.

But... interesting theroretical questions, but why would you want to do that?

evjim
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Location: MT

Re: AC induction motor

Postby evjim » 27 Jul 2017, 08:30

Hi rew, thanks for the reply, the main reason I see to do a 1S design is to eliminate BMS and complicated battery design.

A few years ago I built up a fully custom AC motor with solid copper bar windings, 1 turn per slot. To me, it seems a lot easier to wind and build. I am looking into scaling the design down to ebike wattage of ~1000w. It would be easy to run this thing on 1S. Only thing is, no controller exists for that low of a voltage.

I have thought about the step up converters but wondered if the low voltage would screw with any other I/O thresholds. I think it seems most elegant to use gate drivers at logic level. But, I have spent a good amount of time looking and everything is just a bit to high of a minimum voltage. The legacy MC3PHAC looks like it would work but it is discontinued and no part replaced it. There are individual gate drivers that would do the job, but then there would need to be new software.

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TheFallen
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Re: AC induction motor

Postby TheFallen » 27 Jul 2017, 13:13

1000W at 1s is ~270A.

You've eliminated the 'BMS' and 'complex' battery design and just have to build an ESC capable of power that no one else has managed to do. Good luck with that. :lol:

rew
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Location: Delft, Netherlands.

Re: AC induction motor

Postby rew » 28 Jul 2017, 05:28

You can't get away with using a solid copper bar for windings at higher RPM. The skin effect will cause your effective copper cross section to drop dramatically once you start running fast....

Also suppose I'm "competition" and I use 12S and we're aiming for 1kW.

So I run at about 50V, 20A, so from the battery to the ESC I use 2.5mm2 wires. You'll use 30mm2. I'll use 2000uF, you will use 300000uF: Where I can accept a 1V voltage drop during each PWM cycle, that is unacceptable. Now you need to find a capacitor of that value with a reasonable voltage rating and good high frequency behaviour.

Once you exit the "hobby" MOSFET range, you'll find that "logic level" mosfets are not popular. At those power-levels it becomes general practise to use a real fet driver driven by 12V.

evjim
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Joined: 27 Jul 2017, 03:03
Location: MT

Re: AC induction motor

Postby evjim » 28 Jul 2017, 06:35

Hi Rew, thanks for the reply. I agree there are some negatives, but I think a few positives too. I did skin effect modeling on the larger prototype. There was no effect on current distribution up to 900hz rotational frequency. I plan to model the new motor as well and don't have much concern. I guess the pwm switching may have some skin, but I think that will smooth out.

I agree switching losses can be more significant. I've got a fet picked out that has low rds. I'll link once on a computer

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: AC induction motor

Postby rew » 29 Jul 2017, 19:51

Yes, as you lower the "max required voltage" on mosfets you can get better specs for RDSON. However, you're not going to find mosfets much lower than "20V", or rather, you won't get any improvement if you aim for a lower voltage. So, to reduce absolute current value, you might as well use 4S and 20V mosfets.

But you must realize that the normal VESC uses 1.5 mOhm FETs. You'd be aiming for on the order of 0.1 mOhm.... The legs on the IRFS7530 on the normal VESC contribute significantly to the quoted 1.5mOhm. PCB tracks easily end up above 1mOhm. Even when you make them 0.3" wide, and double copper.

rizanirusli
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Joined: 17 May 2018, 16:39
Location: Surabaya

Re: AC induction motor

Postby rizanirusli » 17 May 2018, 16:45

Hi
Can VESC FOC Vedder be used to drive AC induction motor?
I really need an open source project for FOC induction motor drive, do you have any ideas?
thank you

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: AC induction motor

Postby rew » 22 May 2018, 05:12

Still one year later, the situation is the same: nobody has written the firmware yet.

I'd say that you could give it a go with "foc openloop" and see how close that comes to running the motor acceptably.

rizanirusli
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Joined: 17 May 2018, 16:39
Location: Surabaya

Re: AC induction motor

Postby rizanirusli » 23 May 2018, 02:45

rew wrote:Still one year later, the situation is the same: nobody has written the firmware yet.

I'd say that you could give it a go with "foc openloop" and see how close that comes to running the motor acceptably.

thank you for your response
FOC openloop? I'm sorry i don't understand what you mean
you mean by using VESC with open loop will be work in induction motor?
thanks


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