# 400 Hz Motors



## Sunking (Aug 10, 2009)

Ok I am a bit new here, but I read a thread the other day (cannot find it now) about using 400 Hz synchronous motors for an EV design. Perhaps I am overlooking something but why would anyone use a synchronous motor?


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## major (Apr 4, 2008)

Sunking said:


> Ok I am a bit new here, but I read a thread the other day (cannot find it now) about using 400 Hz synchronous motors for an EV design. Perhaps I am overlooking something but why would anyone use a synchronous motor?


Hi Dereck,

I guess I don't follow you on this. Synchronous motors for EVs? Shure, why not? BLDC are synchronous and used for EVs. I haven't seen a wound field synchronous motor used, but see no reason why it wouldn't work. It has been discussed, like on EVDL, and some guys think there would be advantages over induction motors. Either way, you need an inverter controller. So, 400 Hz is likely a maximum frequency.

That, and there has been some confusion lately with posters about synchronous motors thinking they were induction motors. 

Regards,

major


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## samborambo (Aug 27, 2008)

Sunking said:


> Ok I am a bit new here, but I read a thread the other day (cannot find it now) about using 400 Hz synchronous motors for an EV design. Perhaps I am overlooking something but why would anyone use a synchronous motor?


There's no reason why you can't use 400Hz motors. In fact, at 400Hz, the iron required in the stator and rotor is a lot less, hence the motors are significantly lighter than standard line frequency induction motors. As I understand it, 400Hz aircraft motors are typically asynchonous induction machines.

You can run a standard line frequency (50Hz here) induction motor at 400Hz to get close to 8 times the power due to the increase in speed (24,000 RPM on a 2 pole motor). However, efficiency would suffer due to increase hysteresis losses in the iron. The radial forces acting on the rotor may cause destruction if it is of large diameter. Bearings would probably need upgrading. Flux density is lower, not requiring as much iron material. Windings may be heavier though due to increased skin effect on the conductor. 400Hz motors may possibly use soft ferrite as the iron material to reduce the hysteresis loss instead of laminated silicon steel as found in normal induction machines.

The reduced iron (and therefore weight) is the same reason why switchmode transformers are much smaller for the same power than line frequency transformers.

These guys http://www.400hertz.net/Categories/Motors.htm apparently sell quite a selection of 400Hz gear. Careful with the ratings though, they appear to be peak power ratings in most cases. You need to use the motor across its designed speed range, (possibly overspeed too). A motor such as ME-400-200-416 4 pole, 150kW (peak, I assume), 12,000RPM used at only a maximum of 3000RPM would only produce 37.5kW.

Does anyone want to investigate prices on these motors? I'm curious.

Any VSD that can drive a 50Hz induction motor should be able to learn a 400Hz induction motor.

Sam.


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## Tesseract (Sep 27, 2008)

samborambo said:


> ...
> You can run a standard line frequency (50Hz here) induction motor at 400Hz to get close to 8 times the power due to the increase in speed (24,000 RPM on a 2 pole motor). ...


Argh... _theoretically_ you can do this, but in order to get 8x the power out of 50Hz motor at 400Hz you need to apply 8x the voltage to keep the current the same. At 220VAC the peak-peak voltage is o310V so you would need a ~2500V battery pack to power the inverter 

And then, as you noted, hysteresis losses (among many other, like eddy, proximity, skin, etc..) start reducing the efficiency much more. 

Of course, it is also highly debatable that a 4 pole induction motor's rotor - designed for 3000/3600RPM - would survive at 8x higher RPM.




samborambo said:


> Any VSD that can drive a 50Hz induction motor should be able to learn a 400Hz induction motor...


Probably, but with the caveat that a 220V/10hp 400Hz motor will have much lower inductive reactance than a 220V/10hp 60Hz motor and so the current waveform may have a much higher harmonic content (i.e. - leading to more heating/voltage spikes). Also, the overcurrent trip in the inverter (aka VSD, VFD, etc...) may not react fast enough if it is expecting much higher reactance to slow the rise time of fault currents (that would generally be regarded as poor engineering, but, well... it ain't like you can't find plenty of examples of such every where you care to look).


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## samborambo (Aug 27, 2008)

Tesseract said:


> Argh... _theoretically_ you can do this, but in order to get 8x the power out of 50Hz motor at 400Hz you need to apply 8x the voltage to keep the current the same. At 220VAC the peak-peak voltage is o310V so you would need a ~2500V battery pack to power the inverter


You're right T, _theoretically_. I should've made that clear. Also keep in mind that the motor field can be weakened at higher speeds to reduce the BEMF but that defies the whole point of trying to get more power out of the same motor. 



Tesseract said:


> And then, as you noted, hysteresis losses (among many other, like eddy, proximity, skin, etc..) start reducing the efficiency much more.
> 
> Of course, it is also highly debatable that a 4 pole induction motor's rotor - designed for 3000/3600RPM - would survive at 8x higher RPM.
> 
> ...


Interesting point. Part of the auto-learning feature of most VSDs is learning the reactance of the motor. I'd assume that if the reactance fell outside a defined range, the VSD would refuse to operate that motor. That would be good engineering.


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## bliksem (Aug 3, 2009)

The new Nissan Leaf is using a synchronous motor. Synchronous motors are supposed to be more compact than asynchronous motors. ( I am not trying to 
start a flame war on this issue.) 

I might be wrong , but were always told that synchronous motors need to run
with an encoder or they will run erratic. So only an inverter that have the option for an encoder can be used.

The 400 Hz Engineering motors look like a perfect match for an EV , they seem to be asynchronous but that is beside the point.


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## Amberwolf (May 29, 2009)

It appears to depend on the controller--there are BLDC controllers designed to run sensorless, and there is code available for at least some microcontrollers to run them as sensorless BLDC controllers.
________
Pattaya condominiums


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## samborambo (Aug 27, 2008)

Amberwolf said:


> It appears to depend on the controller--there are BLDC controllers designed to run sensorless, and there is code available for at least some microcontrollers to run them as sensorless BLDC controllers.


There's a problem with sensorless BLDC drive. It's not effective at very low speed or stall since it relies on measuring the BEMF of the non-driven phase to determine the rotor position. Since BEMF is a function of speed, at low speed it simply doesn't work. Most sensorless BLDC implementations I've seen use open loop V/Hz to bring the motor up to a speed it can measure and then changes mode to sensorless. For a traction application like an EV where you need fairly precise control of torque at low speed, you may need hall sensors to determine position.

Sam.


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## vwdevotee (Mar 8, 2008)

Not to be a party pooper, but I contacted 400Hz engineering about that sexy ass motor and was told it's no longer available. Apparently it was actually made by AC Propulsion and they must have pulled it from resale when they stopped answering emails and stuff.


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## Drew (Jul 26, 2009)

As a point of interest exactly what would be the upper limit for the synchronous frequency of an AC motor? Not an existing motor, but the theoretical design limit or whatever the limiting factors would be to a higher drive frequency?


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## samborambo (Aug 27, 2008)

Drew said:


> As a point of interest exactly what would be the upper limit for the synchronous frequency of an AC motor? Not an existing motor, but the theoretical design limit or whatever the limiting factors would be to a higher drive frequency?


The model aeroplane scene uses BLDC motors up to at least 60,000RPM. No reason why you couldn't build a similar spec induction motor. For a two pole motor 60,000 RPM is around 1000Hz.

I think Tesseract and I covered the limiting factors already in this thread.


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## Janis (Jan 27, 2009)

Control Techniques model Commander SK open loop max frequency 1500Hz, Unidrive SP max 3000Hz


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## yarross (Jan 7, 2009)

samborambo said:


> You're right T, _theoretically_. I should've made that clear. Also keep in mind that the motor field can be weakened at higher speeds to reduce the BEMF but that defies the whole point of trying to get more power out of the same motor.


You can rewind the motor stator to adapt it to different speed and/or voltage. At the first glance, you can assume n2/n1 = (U2/U1)*(f1/f2) to maintain the flux and hence the torque at new rated voltage and speed.
The issue with high speed low voltage motors is that they would require fractional turns in their coils.


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## vwdevotee (Mar 8, 2008)

This might be a bigger questuion than I think, but how do they pull of fractional turns and still keep everything balanced? I mean like flux and vibration modes, not just weight.


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## Dennis (Feb 25, 2008)

> You can rewind the motor stator to adapt it to different speed and/or voltage. At the first glance, you can assume n2/n1 = (U2/U1)*(f1/f2) to maintain the flux and hence the torque at new rated voltage and speed.
> The issue with high speed low voltage motors is that they would require fractional turns in their coils.


Every motor repair book I have ever read always shows that something like 10 1/2 turns is the answer for example then you round it. I never seen them say keep the fraction part. I really do not see making it a full turn of one loop to have any significant effect on motor performance at all. I bet motor repair shops also round the turns of the motor when doing voltage changes.


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## yarross (Jan 7, 2009)

Dennis said:


> Every motor repair book I have ever read always shows that something like 10 1/2 turns is the answer for example then you round it. I never seen them say keep the fraction part. I really do not see making it a full turn of one loop to have any significant effect on motor performance at all. I bet motor repair shops also round the turns of the motor when doing voltage changes.


If you obtain 10.72 and you round it to 10.5 it's OK, you have just to slightly change rated values, but I mean REALLY low voltage and high speed. Let's say you obtain 2.83 (a real number). 2.5 and 3.0 it's just too coarse.


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## samborambo (Aug 27, 2008)

yarross said:


> If you obtain 10.72 and you round it to 10.5 it's OK, you have just to slightly change rated values, but I mean REALLY low voltage and high speed. Let's say you obtain 2.83 (a real number). 2.5 and 3.0 it's just too coarse.


Is that really a problem though? You're talking about an overall deviation of RMS voltage. Size the battery voltage and rate the controller to suit.


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## epyon (Mar 20, 2008)

I guess the problem is how to make it so you can do it to any Ac motor and run it , without needing a $10,000.00 controller by it's self . Can I just get any 120 hz controller an 3-phase motor and a power inverter for the battery's and call it a day ? Could it be that simple ? A guy on youtube did it on a ATV , but it was really complicated !


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