Soapbox on regenerative braking

Technical discussion on converting internal combustion to electric
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Soapbox on regenerative braking

Post by Johny » Fri, 24 Jul 2009, 17:18

Electrocycle wrote:I would think that a 4 pole 10-15kw motor wound for around 100v operation (~1450rpm at 50Hz) with a matching controller capable of at least 300v and 30-40kw (100-150A) would be a nice setup for most direct drive or gearbox cars.
I pretty much agree except that I'd up the controller to about 4 times the continuous motor power. More like about 300 Amps.
The controller pricing will change based on it's power so perhaps a moderate power and a high power option?

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Soapbox on regenerative braking

Post by Goombi » Fri, 24 Jul 2009, 17:27

10- 15 Kw is my aim. the chinese AC motors are 2000-4000rpm which will acccomodate gearbox and direct drive.
-------------------------------------
Please look up the Chinese AC motors finally got it loaded
-------------------------------------

uploads/437/Motors_AC.doc
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Soapbox on regenerative braking

Post by Electrocycle » Fri, 24 Jul 2009, 17:32

Johny wrote:The controller pricing will change based on it's power so perhaps a moderate power and a high power option?



yeah that was my moderate power option.
Personally I'd want a super high power version - but then I can't really afford the battery pack for that anyway :P
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Soapbox on regenerative braking

Post by antiscab » Sat, 25 Jul 2009, 02:23

Goombi wrote: A question: You who drive AC/regen car with gearbox-- is it difficult to change gears? when you take your foot of the accelerator? such action will engage regen?!?


how regen is activated is a matter of a setting in the controller.
If you are using a gearbox, you would have 0 throttle mean an idle motor (0 Nm), rather than in regen.

there are lots of options as to how to enable regen, as the input to the controller is either a 0n/off signal, 0-5v braking signal, or both.

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Soapbox on regenerative braking

Post by Goombi » Sat, 25 Jul 2009, 03:22

Can anyone tell me--- if there was a 15 Kw AC setup with controller and programmer at 3000 USD available and working
How many people here will be intersted to get one set?
?
?
?

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Soapbox on regenerative braking

Post by acmotor » Sat, 25 Jul 2009, 03:30

Gearbox ? I'll pass on that Image !
Matt's answer was good !

BLDC uses 3 pickups (hall effect or optical depending on brand) to feedback to control circuit when to switch phase angles. The PWM adjusts the torque. This switching replaces the brushes/commutator of the traditional DC motor.

BLDC is simpler to drive than sync AC or induction. Although many model aircraft emotors are now PM AC rather than BLDC.
BLDC offers less regen torque as the RPM lowers since it typically runs as an 'alternator' whose output voltage is RPM dependent when slowing.
As the voltage drops there is less current able to be pushed back to battery and eventually none.

BLDC can be overdriven to some extent in voltage for higher revs. The limit being the mosfet controller safe voltage. But typically BLDC motor/controller combinations cannot be pushed in current as they are limited to safe values by the controller, unlike a simple series DC that can be pushed until the smoke escapes (but with considerable losses).



Goombi, is that 15kW continuous or peak ?
It would need to be 15kW continous and 45kW peak to be useful and at a useable rev range to suit a gearbox probably i.e. 6000RPM max.

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Post by woody » Sat, 25 Jul 2009, 03:46

Goombi wrote: Can anyone tell me--- if there was a 15 Kw AC setup with controller and programmer at 3000 USD available and working
How many people here will be intersted to get one set?

evcomponents.com has a few AC55 solectrica kits (55kW peak) for USD3500, you'd have to match that to set up a new name at that price.
Motors are cheap and plentiful and heavy, if you get an AC 415v 150 amp controller for USD2000 you'd corner the market.
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Post by coulomb » Sat, 25 Jul 2009, 07:02

One line from the document Goombi uploaded:

Model                           YVF160M-11-50
Rated Power (kW)        11
Rated voltage              380
Rated current (A)          22.1
Rated torque (Nm)        72
Rated speed (RPM)       2000
Max speed (RPM)          4500

Do the motor gurus agree that this is 380 VAC?
Rated = nominal?
Rated power is mechanical power output (not electrical input)?
But then nominal power = nominal speed (in rps) * 2pi * Tnom
= 2000/60 * 6.28 * 72
= 15,100 W = 15.1 kW.

With the 50 in all the part numbers, this suggests 50 Hz 4-pole to me, so these nominal speeds should all be 1500 RPM (or a little less).

In that case we have 1500/60 * 6.28 * 72
= 11,300 W = 11.3 kW

The other sizes seem to agree with this. So I'm thinking they all should be 1500 (or really ~1450 with slip, which works out even closer).

If we believe that the 380 V is an AC figure, and the current is RMS per phase, we have 380 * 22.1 * sqrt(3) = 14,600 VA electrical. That makes the power factor 11/14.6 = 0.753, which seems a little low.

If we take the 380 V as DC, and the current as battery current, then we have 380 * 22.1 = 8,400 W electrical into the controller. There is no way you can get 11 kW from this.

This whole set of motors in that second table ("3-Phase AC Variable Frequency Motor" seems to be pretty standard industrial fare, with only a 9% overvoltage factor (415 / 380 ~= 240 / 220) advantage over motors we can get in Australia. Actually the motors we get here can run at 380 V as well, so really they could be the same thing as far as voltage goes. Since Goombi is interested in lower voltages, I think that rules out that second table.

So the table of interest is the first one. These motors seem to be larger framed and lower efficiency than the ones I've been looking at; presumably because they are designed for such low voltages. But perhaps you could consider these as already undervoltaged industrial motors. So the 10 kW 78 VAC (120 VDC) could be pushed to something like 20 kW continuous (with very good cooling) with a different controller. Perhaps a 240 VAC single phase or 208/220 V three phase controller. However, they have a stated maximum of 4500 RPM, and it's not certain that they could handle 200+ VAC. Presumably also, the manufacturers know how to get the most power from their own motors.
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Post by coulomb » Sat, 25 Jul 2009, 07:25

acmotor wrote: Firstly, AC motors in EVs are not destined to run at a 50Hz limit. The power to weight is not good compared with a higher frequency (coil inductance thus iron mass requirement). Any question there ?
Well, yes. Which one are you saying has the lower power/weight ratio, the industrial AC motor or an AC motor designed for an EV? If the designed for EV motor is designed to run at a higher RPM and therefore higher electrical frequency, won't it need less inductance and therefore need less iron and copper?
The other half of that point is that I feel that for an emotor to be useful it needs to have max power revs of less than 6000 at a frequency > 50Hz e.g. 200Hz, 4 pole if starting with a 50Hz motor.
Otherwise gearbox requirements become specialised.
So you are saying that 4-pole works out better for standard drivetrains if you overvoltage by a factor of 4. But you get the same speeds with a 2-pole motor overvoltaged by 2. But I guess that your point is the more overvoltaging, the better the power to weight ratio. (So a simple "yes" might have sufficed to my original question   Image )
2 pole (nominal 3000RPM) motor would be OK at 100Hz and 6000RPM but would weigh 2 to 4 times as much as a 4 pole motor producing the same power running at 6000RPM (200Hz). This is significant when the 2 pole motor of 15kW may weigh 100kg or more.
Now this is getting closer to the mystery I'd really like solved. More below.
Secondly, the power to weight of 2 pole vs 4 pole of the same nominal kW suggests 4 pole is better in the first place. Any question there ?
Yes. I've noticed this, and the price seems to reflect this to some degree (though it's hard to say because prices are such an infuriating secret). But I can't figure out why that is. Can you explain it? You seem to suggest above that the power/weight ratio of similarly powered 2-pole and 4-pole motors could be as much as 2:1. I'm assuming that you are comparing nominal power, without any overvoltaging. It seems to me that a two pole and 4-pole motor of the same power are much the same thing, just wired differently. Maybe the laminations in the 4-pole can be a bit cheaper since they don't need as much protection from eddie currents.
Thirdly, the commercial EV motor market goes for at least 4 pole
Well, perhaps, but they may have some other reasons for doing that. FOr example, the Prius seems to have 8 poles, but it uses the motors somewhat differently than a standard EV.
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Post by woody » Sun, 26 Jul 2009, 20:24

coulomb wrote:
acmotor wrote: 2 pole (nominal 3000RPM) motor would be OK at 100Hz and 6000RPM but would weigh 2 to 4 times as much as a 4 pole motor producing the same power running at 6000RPM (200Hz). This is significant when the 2 pole motor of 15kW may weigh 100kg or more.
Now this is getting closer to the mystery I'd really like solved. More below.
Secondly, the power to weight of 2 pole vs 4 pole of the same nominal kW suggests 4 pole is better in the first place. Any question there ?
Yes. I've noticed this, and the price seems to reflect this to some degree (though it's hard to say because prices are such an infuriating secret). But I can't figure out why that is. Can you explain it? You seem to suggest above that the power/weight ratio of similarly powered 2-pole and 4-pole motors could be as much as 2:1. I'm assuming that you are comparing nominal power, without any overvoltaging. It seems to me that a two pole and 4-pole motor of the same power are much the same thing, just wired differently. Maybe the laminations in the 4-pole can be a bit cheaper since they don't need as much protection from eddie currents.
From my look at (mostly industrial) induction motors, 2 & 4 pole, you get a fairly constant 3-4Nm peak per kg of aluminium motor, e.g. a 100kg 2 or 4 pole will put out about 300-400Nm peak. This also holds for the AC propulsion-like motor from 400hertz.com.

From our point of view, if we are choosing the winding voltage there isn't much difference between a 120V 4 pole 11kW and a 240V 2 pole 22kW.    For 5000rpm, both have same voltage, current, torque, power, rpm. The only difference is the frequency (~175 for the 4 pole, ~87 for the 2 pole).

In the real world, the ABB 2 pole 22kW 131-008 is about 90kg, the Qin Wei 4 pole 11kW is about 75kg.

So the 2 pole is easier to get in 240V, the frequency is lower, so losses at high RPM are less, but it's 20% heavier and about twice the price.

Why are the 2 poles heavier? A few ideas:
* 4 pole windings are more efficient due to being spaced about 30 degrees rather then 60
* 2 pole motors have to be run much more conservatively due to MEPS and other efficiency ratings being based on power, rather than torque - and more power requires more efficiency - I.E. a 4 pole 15kW motor could be wired as a 2 pole 30kW motor, but the efficiency would only be ~90%, whereas MEPS requires say 93% for a 30kW motor
* more laminations required for 2 pole due to higher frequency
* more mass / cooling required to dissipate double absolute losses at double power.

Some of these apply to over-voltaging, some don't.
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Post by Squiggles » Sun, 26 Jul 2009, 21:05

Are we comparing apples with bananas here?
Surely Ampere-turns has something to do with output.
If a two pole motor has 100 turns per pole and 100 amps applied would it not be less powerful than a four pole with the same turns per pole and same current?
On the other hand if the four pole had only 50 turns per pole....

What I mean is that it seems to me that there is a whole lot more involved than just the number of poles.

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Post by woody » Mon, 27 Jul 2009, 01:48

hmm, the amp turns can be manipulated by increasing the voltage for a given frequency -- this gives more amps / magnetism / torque / power - at the expense of efficiency.
The stator takes a certain amount of magnetism before becoming magnetic itself. this takes power. It also takes power to undo - 100+ times a second. This is one contributor to the loss/heat in an ACIM. Nominal ratings go about 10% into this "over-magnetising" area, but you can go a lot further and get more magnetism at the expense of higher loss.

So I reckon a certain weight of ali in the stator can take a certain amount of magnetism assuming it's in a good motor design. Magnetism creates torque - so weight limits the amount of efficient torque.

If you run the motor at half volts, you'll get half the current / magnetism and 1/4 the torque...

In the basic motor theory there isn't any reason that 4 pole is better than 2, 6, or 8, or 56, but in the available motors, it seems to have an edge...
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Post by acmotor » Mon, 27 Jul 2009, 04:14

woody wrote: ......Nominal ratings go about 10% into this "over-magnetising" area, but you can go a lot further and get more magnetism at the expense of higher loss.
.........
So I reckon a certain weight of ali in the stator can take a certain amount of magnetism assuming it's in a good motor design. Magnetism creates torque - so weight limits the amount of efficient torque.
.........
If you run the motor at half volts, you'll get half the current / magnetism and 1/4 the torque...


Do you mean magnetic saturation ? Normal ratings seem to be something like 1/3 of the magnetic saturation (not 10% into it) otherwise you couldn't get Tmax 3x Tn with linear current to torque ratio up to at least 70% or more of Tmax.
But true, this is not a brick wall, just a case of diminishing returns. i.e. 400% or more Tn is there for the taking. I do this already.

I take 'ali' as a new type of iron !   Image

I'm not certain that I follow '1/2 the volts' woody. Image
Is this 1/2 volts while maintaining the v/f ratio i.e. half the frequency as well ? In that case the torque is still exactly the same = Tn, without question.
If you mean 1/2 voltage / same frequency then I would have thought you have half the torque available if current was half since current == torque.



Still examining the pole number topic .... perhaps I can throw in the original thinking I had when chosing 4 pole 11kW for the Suzi.
My first experiment with ACIM was a very small (1.1kW) 2 pole and a 20:1 gearbox. This was enough to tell me that stall torque (zero RPM torque) was all important with AC. You must have a minimum torque available to take off up a slope in the EV. 11kW is cruise power at 80kmph.
As it happened Tn of 72Nm 11kW 4 pole emotor = ICE motor torque and with 3:1 Tmax this was close to the 1st gear ratio. Now if I used a 2 pole motor of 11kW it would have 36Nm of torque .... simply not enough.
I would need a 22kW 2 pole for the same torque as the 11kW 4 pole.

The 0-40kmph performance is better than original ICE but above that the voltage limitation cuts in.
Now it is apparent that to get the 80 or more kmph at full torque I need to change the emotor voltage by 1/2, 1/3 or even 1/4.
If I used a 2 pole I would have 1/2 the torque as mentioned and this would not be acceptable and I couldn't do anything to improve it. However I can rewire/rewind the 4 pole and get the required performance.

It appears from data sheets e.g. ASEA that the 4 pole (160M) 11kW 80kg (yes there are smaller) is equivalent to the torque of a 22kW 2 pole (72Nm) but in 180M frame and 150kg of the same vintage motor.
Yes there are better combinations available but still the 2 pole falls short of the 4 pole in power to weigh at the same kW. If you double the 2 pole kW to retain the Nm then the motor is somewhere between bigger and BIGGER. Please present any good combinations you find (that are available in Oz)

OK I'm talking direct drive here. You can use a gearbox to make up for an underpowered / undertorque motor up to a point only. But ... Once you haven't enough torque in first gear you are out of business. Once you can't climb a 1 degree slope at 100kmph you are out of business.

Remember though that the 4 pole at 4x frequency will give a peak of up to 12x power as I have demonstrated. A 2 pole at 2 times freq. (both 6000RPM) will only supply up to 6 x peak. On both accounts, original size / weight and potential peak power the 4 pole wins. No wonder the prius went even further to 8 pole !

edit: Duh! forgot to paste !
Image
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Post by coulomb » Mon, 27 Jul 2009, 05:42

acmotor wrote: Do you mean magnetic saturation ? Normal ratings seem to be something like 1/3 of the magnetic saturation (not 10% into it) otherwise you couldn't get Tmax 3x Tn with linear current to torque ratio up to at least 70% or more of Tmax.
I wish Weber was still around to answer this sort of question. My understanding is that the field (stator) gets magnetised essentially from the reactive component of the current. So when you close to triple the real component of the current for triple the nominal torque, the magnetising current can stay about the same, causing the power factor to move closer to unity.

Warning: technical content alert Image
Like this:

Image

So the red is the real current, and the green is the imaginary, magnetising current. Here we have the classical 3:4:5 right angled triangle, with cos Φ1 = 0.8 (4/5). So the motor is drawing 5 units of current at a power factor of 0.8. Now we triple the current, and arrange for the magnetising current to remain the same. Then we have the larger triangle, with 12 units of real current, and still 3 units of imaginary current, for a total of about 12.4 units (sqrt (12² + 3²)), and a new power factor of cos Φ3 = 12/12.4 ~= 0.968.

In fact, I believe that the "distance up the magnetic saturation curve" is set essentially by the V/f ratio. By using a bigger V/f ratio, you move closer to saturation, thereby trading efficiency for more torque. I suppose that for low demand driving (e.g. 60 km/hr on a flat road), you could even reduce the V/f ratio to get better efficiency at the cost of a lower maximum torque.

So Woody may well be right in saying that the motor is usually running about 10% into the "non linear region" (it's all very gradual of course, so any boundary between the so-called linear region and the non-linear region is open to interpretation). That seems to be about the sweet spot for machines running 24/7 with a constant torque load. But with EVs, we have vastly different torque needs, so adjusting the V/f ratio could be profitable, possibly in both directions.
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Post by woody » Mon, 27 Jul 2009, 07:01

acmotor wrote:
woody wrote: ......Nominal ratings go about 10% into this "over-magnetising" area, but you can go a lot further and get more magnetism at the expense of higher loss.
.........
So I reckon a certain weight of ali in the stator can take a certain amount of magnetism assuming it's in a good motor design. Magnetism creates torque - so weight limits the amount of efficient torque.
.........
If you run the motor at half volts, you'll get half the current / magnetism and 1/4 the torque...


Do you mean magnetic saturation ? Normal ratings seem to be something like 1/3 of the magnetic saturation (not 10% into it) otherwise you couldn't get Tmax 3x Tn with linear current to torque ratio up to at least 70% or more of Tmax.
Sorry I was talking stators - I thought you get Tmax 3x Tn by increasing the slip, not the stator magnetism - i.e. the rotor bars cut more magnetic field => current goes up and hence the rotor magnetism goes up.

DOL implies same stator magnetism for all loads, but you still get Tmax / Tn.
acmotor wrote: But true, this is not a brick wall, just a case of diminishing returns. i.e. 400% or more Tn is there for the taking. I do this already.
Yes I think increasing V/F overmagnetises the stator to a higher degree.
acmotor wrote: I take 'ali' as a new type of iron !   Image
Aluminium is the stator in an aluminium motor? But you can't permanently magnetise aluminium, so how can you over-magnetize it.
acmotor wrote: I'm not certain that I follow '1/2 the volts' woody. Image
Is this 1/2 volts while maintaining the v/f ratio i.e. half the frequency as well ? In that case the torque is still exactly the same = Tn, without question.
Yes, I can be vague at times. I meant 1/2 the volts that the nominal V/F ratio suggests.
acmotor wrote: If you mean 1/2 voltage / same frequency then I would have thought you have half the torque available if current was half since current == torque.
Nah, I think it's 1/4. It's the same as operating in the higher frequency ("field weakening zone" - after run out of voltage to keep up with VF) : double frequency = quarter breakdown torque. Also Star/Delta starting gives 1/3 the starting torque/current despite being only sqrt(3) * the voltage.
acmotor wrote: Still examining the pole number topic .... perhaps I can throw in the original thinking I had when chosing 4 pole 11kW for the Suzi.
My first experiment with ACIM was a very small (1.1kW) 2 pole and a 20:1 gearbox. This was enough to tell me that stall torque (zero RPM torque) was all important with AC. You must have a minimum torque available to take off up a slope in the EV. 11kW is cruise power at 80kmph.
As it happened Tn of 72Nm 11kW 4 pole emotor = ICE motor torque and with 3:1 Tmax this was close to the 1st gear ratio. Now if I used a 2 pole motor of 11kW it would have 36Nm of torque .... simply not enough.
I would need a 22kW 2 pole for the same torque as the 11kW 4 pole.

The 0-40kmph performance is better than original ICE but above that the voltage limitation cuts in.
Now it is apparent that to get the 80 or more kmph at full torque I need to change the emotor voltage by 1/2, 1/3 or even 1/4.
If I used a 2 pole I would have 1/2 the torque as mentioned and this would not be acceptable and I couldn't do anything to improve it. However I can rewire/rewind the 4 pole and get the required performance.

It appears from data sheets e.g. ASEA that the 4 pole (160M) 11kW 80kg (yes there are smaller) is equivalent to the torque of a 22kW 2 pole (72Nm) but in 180M frame and 150kg of the same vintage motor.
Yes there are better combinations available but still the 2 pole falls short of the 4 pole in power to weigh at the same kW. If you double the 2 pole kW to retain the Nm then the motor is somewhere between bigger and BIGGER. Please present any good combinations you find (that are available in Oz)
Well, from the sheet I have put together with specs of about 60 ACIMs (50 ABBs, 5 or 6 CMGs, a trojan and a qin wei):
The best T(max)/kg is the 92kg ABB 132-316 15kW 4 pole, with 97.8 * 4.0 / 92 = 4.25 Nm/kg (~AU$1000)
Next 2 are Johny's picks:
the unobtainium 61kg CMG 132MB-38 11kW HO with 72.7 * 3 / 61 = 3.58 Nm/kg
the 72kg qin wei 11kW 132 with 72.3 * 3.5 / 72 = 3.5 Nm/kg
The next 10 (2.98 - 3.51 Nm/kg) are 9 ABB 4 pole motors (162 034, 132 003, 132 315, 162 102, 182 103, 162 103, 132 006, 132 007, 182 033) ranging from 11 to 30 kW, 63 - 177kg, 132 - 180 frame, plus the CMG 160-42.
Then comes Weber & Coulomb's pick, the ABB 131-008 22kW @ 95kg 72.6*3.8/95 = 2.9 Nm/kg. (~AU$2000)

The "pair" of the SI units' favourite is possibly the 132-005 11kW @ 76kg 72.6*3.0/76 = 2.85 Nm/kg or about the same.
acmotor wrote: OK I'm talking direct drive here. You can use a gearbox to make up for an underpowered / undertorque motor up to a point only. But ... Once you haven't enough torque in first gear you are out of business. Once you can't climb a 1 degree slope at 100kmph you are out of business.
I still like the gearbox since the ACIM power curve has a fairly sharp peak (unless you are battery limited).
Star/Delta/Series/Parallel switching would also give you multiple peaks for a lot less weight/efficiency wasted.

I am still thinking direct drive with a large enough rewound motor and controller to suit is going to be right for me.
acmotor wrote: Remember though that the 4 pole at 4x frequency will give a peak of up to 12x power as I have demonstrated. A 2 pole at 2 times freq. (both 6000RPM) will only supply up to 6 x peak. On both accounts, original size / weight and potential peak power the 4 pole wins. No wonder the prius went even further to 8 pole !
From a quick scan of ABB cataloge:
99kg 8 pole is 72 * 2.8 / 99 = 2.0 Nm/kg
99kg 6 pole is 73 * 3 / 99 = 2.2 Nm/kg

So not much good for ACIM, probably permanent magnet is different
acmotor wrote: edit: Duh! forgot to paste !
Image


Yes, my email version of your reply was a bit light on in content :-)
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Post by woody » Mon, 27 Jul 2009, 07:04

coulomb wrote:
acmotor wrote: Do you mean magnetic saturation ? Normal ratings seem to be something like 1/3 of the magnetic saturation (not 10% into it) otherwise you couldn't get Tmax 3x Tn with linear current to torque ratio up to at least 70% or more of Tmax.
I wish Weber was still around to answer this sort of question. My understanding is that the field (stator) gets magnetised essentially from the reactive component of the current. So when you close to triple the real component of the current for triple the nominal torque, the magnetising current can stay about the same, causing the power factor to move closer to unity.

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Like this:

Image

So the red is the real current, and the green is the imaginary, magnetising current. Here we have the classical 3:4:5 right angled triangle, with cos Φ1 = 0.8 (4/5). So the motor is drawing 5 units of current at a power factor of 0.8. Now we triple the current, and arrange for the magnetising current to remain the same. Then we have the larger triangle, with 12 units of real current, and still 3 units of imaginary current, for a total of about 12.4 units (sqrt (12² + 3²)), and a new power factor of cos Φ3 = 12/12.4 ~= 0.968.

In fact, I believe that the "distance up the magnetic saturation curve" is set essentially by the V/f ratio. By using a bigger V/f ratio, you move closer to saturation, thereby trading efficiency for more torque. I suppose that for low demand driving (e.g. 60 km/hr on a flat road), you could even reduce the V/f ratio to get better efficiency at the cost of a lower maximum torque.

So Woody may well be right in saying that the motor is usually running about 10% into the "non linear region" (it's all very gradual of course, so any boundary between the so-called linear region and the non-linear region is open to interpretation). That seems to be about the sweet spot for machines running 24/7 with a constant torque load. But with EVs, we have vastly different torque needs, so adjusting the V/f ratio could be profitable, possibly in both directions.
I like everything you say :-)

I'm pretty sure VFDs drop the voltage to lower torque / save power rather than just dropping slip.
And danfoss torque boost is increasing it.
I'm sure drag racing ACIM EVs won't run on industrial V/F ratios :-)
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Post by acmotor » Mon, 27 Jul 2009, 09:11

quote woody.... "Also Star/Delta starting gives 1/3 the starting torque/current despite being only sqrt(3) * the voltage."

This is DOL locked rotor situation, not an EV parameter when using a VFD, so I wouldn't comment, but I see your thinking.

Ah, are we talking the same thing re 1/2 voltage ? Tmax is 1/4 but Tn (that I was talking) is 1/2 Yes ?

Stator is laminated iron in an industrial 50Hz motor. The outer case (not part of any magnetic circuit) can be ali, steel, cast iron or anything to hold the stator and bearings in place.
Aluminium itself is non magnetic of course, but would result in significant eddie current losses if it were the core of of an AC fed magnet.
'Aluminium motor' in the 3PIM world means aluminium case, nothing more.

Ironless stators use the Lorenz (from memory) force of magnetic field acting directly on conductors. This is the pancake and hub type motors with PMs. Typically axial flux construction from memory. TJ would be the expert there.

coulomb, now we need a vector diagram to explain the linear increase in torque with current between Tn and 70% or so of Tmax because it is published data without the losses that you suggest. Heat seems to be the limiting factor due to the resultant current (IR).

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Post by coulomb » Mon, 27 Jul 2009, 15:03

? I predict no increased iron losses, but obviously copper losses will increase with the square of the current. You said yourself that torque is proportional to current; I'm saying it is proportional to real current, not total current.

Actually, copper losses would be proportional to the square of total current, not real current. So a tripling of torque and hence power if the speed is constant would only result in (12.4/5)^2 instead of (12/4)^2. So that's 6.2 instead of 9.0, a handy "saving".
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Post by acmotor » Mon, 27 Jul 2009, 17:14

I think we are saying the same thing. Losses increase in the Tn to 70% (maybe more) of Tmax area mainly due to copper loss (this should be I^2R). The efficiency as a % for the motor remains much the same though. This I found also with the little motor at 12x Tn. The overall efficiency remains much the same. The losses as a % remain the same. They just become (obviously) a greater Watt value and this creates heat which will limit the time for which the overload can be maintained. i.e. losses don't increase as a proportion of the applied power, they just increase in Watts as they are a fairly constant % of the applied power.

This is what leads me to thinking that we are not hard up against saturation. Agreed with the v/f determinig this saturation condition though. I wonder though that if it is ampere turns that push the iron toward saturation then as the motor current increases above Tn why do we not clearly see some nonlinearity from saturation ?

This is all because I know what I have measured, even though I don't have the motor theory to explain it.

Perhaps the fact that the copper losses are in fact such a small percentage of total power, doubling or trebling them is still just a small percentage. This may also be balanced by other efficiency changes as the frequency changes ?

Another hyjacked thread !
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Post by coulomb » Mon, 27 Jul 2009, 17:48

acmotor wrote: I think we are saying the same thing. Losses increase in the Tn to 70% (maybe more) of Tmax area mainly due to copper loss (this should be I^2R). The efficiency as a % for the motor remains much the same though. This I found also with the little motor at 12x Tn. The overall efficiency remains much the same.
Yes, I think we probably are saying much the same thing. With the small motor, it has a fairly low efficiency, so iron losses are a bit higher as a percentage than with larger motors. I'd expect to see this as a lower power factor... I just checked the label that you considerately photographed, and the value for cos phi is missing... grr. Perhaps they were embarrassed about it. So with the higher reactive current, tripling the real current would result in even less than a 6.2:1 increase in copper loss. Hmm, I'd still expect at least 50% more copper loss per kW of output, though.
I wonder though that if it is ampere turns that push the iron toward saturation then as the motor current increases above Tn why do we not clearly see some nonlinearity from saturation ?
I think you are effectively asking how does the tripling of real current, even though the reactive current is constant and set by the V/f ratio, get ignored by the basic law that ampere turns cause magnetism. A good question, and I think the answer has to do with the phase relationship to the voltage.
This is all because I know what I have measured, even though I don't have the motor theory to explain it.
Sure, can't ignore the experimental result.
Perhaps the fact that the copper losses are in fact such a small percentage of total power, doubling or trebling them is still just a small percentage. This may also be balanced by other efficiency changes as the frequency changes ?
I doubt that the copper losses are so small as to make little effect; the copper and iron losses are the two biggies. I also can't see any other losses decreasing as the frequency increases. Unless it has something to do with inductance.
Another hyjacked thread !

Yes. We're so lazy at moving to new threads as needed.

Edit: formatting
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Post by woody » Mon, 27 Jul 2009, 17:55

acmotor wrote: This is what leads me to thinking that we are not hard up against saturation. Agreed with the v/f determinig this saturation condition though. I wonder though that if it is ampere turns that push the iron toward saturation then as the motor current increases above Tn why do we not clearly see some nonlinearity from saturation ?

This is all because I know what I have measured, even though I don't have the motor theory to explain it.
The hijacking continues...

I think the amps increasing under greater load at same V & F is nearly all passed onto the rotor (active current) to do actual work and so doesn't contribute to magnetising.

I'd say by programming in some danfoss torque boost of our own into your coffee cup motor by telling the VFD it's a 500V motor, not a 400V, you'll get a fair whack more peak torque (not as much as you'd expect < 44%) but a fair whack less efficiency.

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Post by Johny » Mon, 27 Jul 2009, 18:09

woody wrote:I'd say by programming in some danfoss torque boost of our own into your coffee cup motor by telling the VFD it's a 500V motor, not a 400V, you'll get a fair whack more peak torque (not as much as you'd expect < 44%) but a fair whack less efficiency.
I wonder whether you can treat this like a transformer. With a transformer under no load, wind up the voltage until there is a non-linear rise in current. That generally is the last value before the no-go zone, where is generates lots of heat - saturation.

With an ACIM and no load, set a middle range speed and increase the v/f ratio (holding speed/frequency constant) until the motor current exceeds what you would project for the applied voltage.

Cumbersome to try because you will have to stop the motor each time and set the motor voltage parameter.

When you hit the "kink" in the current curve does this then correspond to the maximum v/f that you can use under load?
Can we then calculate the resulting torque increase before saturation?

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Post by acmotor » Mon, 27 Jul 2009, 18:37

Good,
This saturation area is one I have long wanted to have a handle on.

Time for new thread though... here...

viewtopic.php?p=15592&t=1327#p15592

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Post by coulomb » Sun, 24 Jan 2010, 17:11

Richo wrote:
-----------AC SYSTEM---------
AC Induction motor 7.5kW
0-4500 RPM
AUD $653.40 INC GST **
No sea
Freight $Local pickup
WEIGHT 52kg

CONTROLLER 1238-75 96V 550A
USD$1000
Air $180
WEIGHT $? Prob around 12kg or less as well.

**Motor requires additional rewind for 96-110V AUD$800.

----------------------------
...
And AC AUD$2930

Richo, where can you get a Curtis 1238-75XX for US$1000?

Per Johny's email to ThunderStruck, it's US$1800 plus US$180 shipping:

viewtopic.php?p=16550&t=1369#p16550

The only price I've seen (apart from being bundled with motors and displays) is over $5000 from Bylong Industries in Victoria.

Maybe that US$1000 was a typo?

Edit: Johny != Woody !
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Post by photomac » Tue, 16 Feb 2010, 20:35

Ian - your arguments are convincing when I do the math too.
Regenerative breaking seems soooo logical until you compare it's energy gain (little) to the losses of rolling resistance (surprisingly high). Having driven a non-regenerative EV down Kalamunda Hill (Gooseberry Hill actually) it is very clear that the normal break pads do get an extra workout. So - regenerative breaking becomes attractive again - not so much for energy recovery but 'accustomed' handling behaviour of a vehicle.
Also - with low rolling resistance tyres - are their handling characteristics comprimised noticably?
My brain is running out of "quandary" solving cells. Oh for a perfect world!

Matt

ps - does a regen incident count as a 'cycle' on a battery? Will repeated regen incidents reduce battery life or have no real affect?
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