# what do i need to buy to control the speed of a 3 Phase Induction Motor?



## cfckevmccfc (Mar 10, 2010)

Hi i am building an EV theoritically and am using a 3 Phase Induction Motor. Would i be right in saying that i need a VFD to control the speed and if so where would a find one to substain a high powered motor? any help appreciated thanks


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## DawidvC (Feb 14, 2010)

How big is your motor. For EV application you want to size your invertor (VFD) to be able to deliver at least 2.5 times the motor rated current, at the rated motor voltage.

Please note that you want a VFD that use Vector control of some kind, or field oriented control, as their control strategies ensure that more torque is available when the motor start.

To make your ev feel like a ICE-driven car, you should look for a VFD with vector control which allows you to control the current OR torque directly. This will give a close approximation of ICE-powered accelerator pedal feel.

Dawid


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## cfckevmccfc (Mar 10, 2010)

The motor is rated at 75kW and the line voltage is 200V. I used Iline=Pt / 1.732 x Vline x 0.9 to get 241Amps. Would you know anywhere which would sell a VDF at this rating?


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## DawidvC (Feb 14, 2010)

Try a Control Techniques reseller. Their Unidrive range can run direct of a DC supply. When you speak to one of their sales people, make sure they understand that. When they ask for motor detail, quote 460V 115Hz 400A for the motor size.

Ask for either an open drive chassis or totally enclosed (IP65) drive with watercooling.
This may seem a bit extreme, but with a 200V motor you can make it run faster than base speed without losing torque.

Dawid

PS - the 115Hz is for 50Hz motor, if the motor is rated 60Hz, it comes to 138Hz


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## etischer (Jun 16, 2008)

LOL, you want him to buy a 320kw / 460v inverter for his 75kw / 200v motor?

You'd need 87kwh (1800lbs) of thundersky cells at 3C to pull that much power. 






DawidvC said:


> Try a Control Techniques reseller. Their Unidrive range can run direct of a DC supply. When you speak to one of their sales people, make sure they understand that. When they ask for motor detail, quote 460V 115Hz 400A for the motor size.
> 
> Ask for either an open drive chassis or totally enclosed (IP65) drive with watercooling.
> This may seem a bit extreme, but with a 200V motor you can make it run faster than base speed without losing torque.
> ...


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## DawidvC (Feb 14, 2010)

If you keep your V/Hz ratio constant, you can run a 200V motor at 460V. Your motor will now be 172kw instead of 75kw, and your base speed will be 4100rpm for a 4 pole motor.

The additional capacity allows you to produce the motor's maximum torque, i.e. approximately 2.5 times the nominal rate.

ALL industrial motors are rated at their nominal torque and speed. This allows them to run at maximum power 24/7. This rating is not needed for EV applications. It is much more useful to work on the motor maximum ratings, but nobody rates them as such. Therefore we have to calculate what the motor may be capable of, hence the seemingly ridiculous figures.

The Australian EV forums have a lot of work in this regard. They recommend for a small car a ACIM betweem 11 and 22kw, 4pole, rewound for 100V, with appropriate invertor, which will be in the region of 100kw.

We use a lot of large ac motors at work, and DOL starting current on some of these motors peak at 12 time nominal. The downside is that you can only start the motors once or twice an hour. So there is plenty of scope for experimentation for us as far as ac motors are concerned.

Dawid


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## Olaf-Lampe (Feb 24, 2010)

The inverters also have nominal and maximal ratings. You don't need a 100kW nom. inverter for a 100kW peak motor.
Also people often mixup between phase current (motor) and DC-current ( inverter).
During acceleration the phase current is max. but dc current is pretty low. No problem for a smaller inverter. Only constant high speed is critical for the inverter. ( and for the batteries )

-Olaf


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## DawidvC (Feb 14, 2010)

Sorry Olaf, I should have made it clearer. If the nominal rating of the invertor is 100kw, you should get a peak power of between 160kw and 200kw, depending on manufacturer.
Using the australian method with rewound motors, you can expect about 80kw (after losses) from your 22kw motor at 4 times the speed.

As you can overload your motor for a short time (at least a minute) to at least 2.5 times, your nominal 1700rpm 22kw motor will now be 200kw at 4200rpm.

please see their forum at http://www.aeva.asn.au/forums/forum_posts.asp?TID=1237

You can also pm Coulomb or CroDriver for more details on this trick, they are also active on the Australian forums 

If people REALLY want to play with invertors they should see the work etischer did on his, http://etischer.com/awdev/ 

I hope this clear it up. I have mentioned power, not current or voltage, because you need to convert to and from phase current for the ac motor. Using the power we can sidestep that. Unless someone wants to convert a small invertor to handle the 75kw motor mentioned, finding an invertor for a 200V motor of that size is really difficult. I would think it would be an EV-only invertor. Standard motors that size are all higher voltages, which is why I suggested using a standard invertor and higher speed - and higher power as well.

Reagrds
Dawid


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## cfckevmccfc (Mar 10, 2010)

DawidvC said:


> Sorry Olaf, I should have made it clearer. If the nominal rating of the invertor is 100kw, you should get a peak power of between 160kw and 200kw, depending on manufacturer.
> Using the australian method with rewound motors, you can expect about 80kw (after losses) from your 22kw motor at 4 times the speed.
> 
> As you can overload your motor for a short time (at least a minute) to at least 2.5 times, your nominal 1700rpm 22kw motor will now be 200kw at 4200rpm.
> ...


 


what voltage size would you expect for this motor? i can look around for a smaller power rated motor but i am trying to produce a reasonably fast EV set up with a decent milage. Could you give me an example set up that could produce this?


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## DawidvC (Feb 14, 2010)

If you want to use a standard motor, try ABB, Siemens or one of the other big industrial motor suppliers. Check their catalog for the smallest (frame size) motor in the 18 - 22kw range, that is either rated 380/400/415V Star or 230V Delta. This should give you a motor with the capability to produce more than 30kw nominal, which will translate to at least 75kw maximum. 

This kind of power at a nominal 3000rpm should give you the same or better perfomance than most small cars. If you want more performance I would suggest either familiarising yourself with this and the other forums where there really are a lot of information on "hotrodding" motors and invertors, or get hold of those members of this and the australian forums who have done some good work in that regard.

If you do not know electrical motor theory, there are plenty of resources on the web. Some of the best information I have found came from links in this website. Even if you know a little, it is still worthwhile perusing these link. A simple search of this forum should give you plenty of material.

Dawid


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## aeroscott (Jan 5, 2008)

dawid , just finished looking the 100 volt rewire test , great stuff . ps can just imagine the power levels with low pressure (5 psi ) h2 cooling , just like the big boys .


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## DawidvC (Feb 14, 2010)

Great, aint it!!

I got the small invertor to turn into a monster a la etischer, I now need a motor bigger than the 5.5kw 575V60HZ motor I experiment on, and a body to stick it all in.

Oh, I forgot the battery

For 3ph ACIM, the AEVA is one of the best. Plenty of real knowledgable people over there.

Hey, if any of you Aussies are following this, forward the Bulls!! 

Dawid


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