# DYNO RESULTS: Induction motor power curve



## Stiive (Nov 22, 2008)

Just looked at the manufacturers website (http://shop.electro-vehicles.eu/shop/details.asp?prodid=EVE02&cat=0&path=47,60) which states the nominal speed of the motor is 3,600RPM.

nsync = (120*f) / Poles

Therefore shouldnt the nominal frequency be (4*3600)/120 = 120Hz?

Maybe thats where its all gone wrong, which again means the motor name plate is wrong again!! 
OR assuming the voltage nameplate setting is right at 210V, then the v/f would be 210/120 = 1.75.... If this is true then it means the second theory is right that the controller uses the over-voltage to increase speed without field weakening, then the increased v/f ratio is allowing the motor to run more optimally, drasitcally increasing the power.

Looking at the torque/speed graph supplied it seems the nsync should be even lower at 3,000 RPM at the end of the constant torque region... What's going on here?

I'm confused :S


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## peggus (Feb 18, 2008)

If you're getting more power in field weakening region I would suspect your motor parameters are not set up right.

By the way, what is INOM and VMAX? Is it phase current/voltage or motor voltage? or battery current/V, is it RMS or Peak? 
I can't seem to get the numbers to work out either way.


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## Stiive (Nov 22, 2008)

Hi, thanks for your reply. It's a bit hard to tell really, the motor parameters are just given as the nominal motor current and voltage without specifying. 
The nominal motor current is entered as a percentage of the nominal current output capacity of the controller. The current readout from the inverter is then given as a percentage of the nominal current value entered, so your reading a percentage of a percentage which makes it hard to correlate back to any real time data. However looking through some of the videos the current seems to be pretty spot on with the measured DC bus current.
The motor voltages would be nominal and maximum Voltage the controller suppiles the motor though PWM phase to phase. I think they must both be RMS but I'm only guessing. The nominal value could b RMS and the max could be the peak of the PWM or something but without a buck/boost converter in the controller I don't see how this is possible, and it doesn't make alot of sense anyway


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## Johny (Jul 21, 2008)

If this was an industrial AC motor I would say that it's running in Delta configuration where the nameplate specifications were for Star - or a 2 pole motor where you are expecting a 4 pole.
Are there other motors in their range that are 2 pole?

The specs make me think it's a 4 pole motor which would put the knee in the power curve at 3000 RPM for 100 Hz (or 3600 RPM for 120 Hz), but a 2 pole would be twice that speed for the same frequencies with half as much torque throughout. Perhaps this motor has been mis-labeled and is really a 2 pole.

Probably not possible but I should put it out there.


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## s2156945 (Apr 15, 2009)

When a4x4kiwi (http://a4x4kiwi.blogspot.com) took his ute to a Dyno day (2 years ago- http://a4x4kiwi.blogspot.com/search/label/results ), he had all sorts of trouble.

Something which may deflate your power + torque readings may be the very fast acceleration on a dyno - electric motor controllers have acceleration ramps etc, but a dyno is allowing the car to accelerate much faster than it would on the road.

I.E. if the dyno is just a spinning weight with a know moment of inertia - the dyno doesn't "brake" the weight much, it just measures how long it takes for the car to spin it up. At low speed the braking may be so low that the acceleration ramp of the electrical motor controller is keeping the acceleration low.

Can the dyno operator beef up the resistance, or make it kick in earlier?

Have you driven this on the ground yet? Does it take off at 5000rpm? Does the ground performance work back to the same torque figures?

You should be able to do starting/stall torque measurements on the motor with an arm and a scale, or in the car by pulling on a strain gauge or pushing against one.

In an normal car you'd burn the clutch, but in an EV these things are possible (for 10-15 seconds at a time - you'll be warming the motor without any cooling fan).

cheers,
Woody


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## major (Apr 4, 2008)

Stiive said:


> EVE M2-AC30-L motor (30kW nominal, 60kW peak)
> 
> 
> 
> ...


I suspect that your dyno RPM is off by a factor of 2 therefore you calculate twice the power. So instead of 121kW at 6000RPM it is really 60kW at 3000RPM which agrees with the published motor curve 

There is no way you can carry 190Nm torque out to 6000RPM on that motor unless you have a 600V battery.

major


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## Stiive (Nov 22, 2008)

The software also suggests that the motor is making the most power at 5,500 RPM. 
Anyway, how could the motor make max power at 3,500 RPM when its synchronous speed is set to 5,250 RPM?

Tonight were going to try dyno again with a much lower nominal frequency (about 120Hz) and adjust the v/hz ratio until we get a decent power curve with no whine (saturation).

Any thoughts on the implications of changing the nominal frequency from its rated if the v/hz ratio is kept constant? Not that i trust the namesplates 175Hz as it doesnt match the torque curve provided


Stefan


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## Stiive (Nov 22, 2008)

s2156945 said:


> I.E. if the dyno is just a spinning weight with a know moment of inertia - the dyno doesn't "brake" the weight much, it just measures how long it takes for the car to spin it up. At low speed the braking may be so low that the acceleration ramp of the electrical motor controller is keeping the acceleration low.


I have been told by the dyno guy that our dyno isn't that type, and it uses some sort of force leaver to measure the torque. Aparently by measuring the force required to keep the speed constant at small incremental steps. Thats how i understood it anyway


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## Stiive (Nov 22, 2008)

Johny said:


> The specs make me think it's a 4 pole motor which would put the knee in the power curve at 3000 RPM for 100 Hz (or 3600 RPM for 120 Hz), but a 2 pole would be twice that speed for the same frequencies with half as much torque throughout. Perhaps this motor has been mis-labeled and is really a 2 pole.
> 
> Probably not possible but I should put it out there.


We thought this for a long time due to the obvious v/f label mismatch. However the motor manufacturer assures us all the parameters are correct and although its not labelled, that the motor is indeed 4pole

:S


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## Johny (Jul 21, 2008)

There is still something very wrong with those figures.
The torque should have been relatively constant to 3600 RPM - instead it's increasing???
How does the controller measure the motor speed? Is it sensorless or use an encoder?


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## pm_dawn (Sep 14, 2009)

Stiive said:


> So anyway, had the car on the dyno a few days ago for the first time; but with our rated settings, we were only producing less than 20kw which was less than exciting. We then slowly increased the current with interesting results;
> 
> 
> 
> ...


Well if you compare the last 5000rpm run with the last 6000rpm run the torque is pretty much the same but power is more than twice in the 6000rpm run, That cannot be right. 122 Nm torque at 6000 rpm would give about 122x6000/9549 = 76,65Kw 
The torque 120 and 5000 rpm would give 120x5000/9549 = 62,8 Kw.

Some of these numbers dont add up.....

Regards
/Per


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## Johny (Jul 21, 2008)

Sorry I forgot to ask this one too.
I see that the chart you have posted says "Max RPM" in the left column.
Where is the measured RPM to go alongside the torque figure?


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## etischer (Jun 16, 2008)

Were you measuring battery amps and voltage, that will give you a quick reality check to see if your dyno numbers make sense.


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## Stiive (Nov 22, 2008)

Johny said:


> There is still something very wrong with those figures.
> The torque should have been relatively constant to 3600 RPM - instead it's increasing???


Indeed



Johny said:


> How does the controller measure the motor speed? Is it sensorless or use an encoder?


FOC with a 64 pulse 2 channel encoder



Johny said:


> I see that the chart you have posted says "Max RPM" in the left column.
> Where is the measured RPM to go alongside the torque figure?


The max torque and power always happened at maximum RPM



etischer said:


> Were you measuring battery amps and voltage, that will give you a quick reality check to see if your dyno numbers make sense.


Yeh we were, but it was hard to capture the volt/amps at the end as it happened in a split second. The volts*amps were about correct for the power the dyno said it was producing


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## peggus (Feb 18, 2008)

Well, a motor simply won't behave like your dyno curves show unless the controller is commanding it to, or the load isn't fully loading it. There must either be something wrong with the controller parameters, or, the dyno doesn't work right above 5000 RPM. Major makes a good point as always, given the manufacturers data you should not be able to get peak torque at 6000RPM without doubling the pack voltage, 2x288V.

If you instrument the motor, measure phase current and motor voltage, I think you'll find that the dyno is lying to you above 5000RPM.


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## Stiive (Nov 22, 2008)

pm_dawn said:


> Well if you compare the last 5000rpm run with the last 6000rpm run the torque is pretty much the same but power is more than twice in the 6000rpm run, That cannot be right. 122 Nm torque at 6000 rpm would give about 122x6000/9549 = 76,65Kw
> The torque 120 and 5000 rpm would give 120x5000/9549 = 62,8 Kw.
> 
> Some of these numbers dont add up.....
> ...


Sorry yeh seems like there was a problem recording the last data set. Unsure what the torque was but the power definetly was above 100kW. We thought there was something terribly wrong and promptly turned off the car and checked temperatures, voltages etc


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## s2156945 (Apr 15, 2009)

etischer said:


> Were you measuring battery amps and voltage, that will give you a quick reality check to see if your dyno numbers make sense.


+1 on etischer's comment.

Also the 190Nm is not way above what the published/theoretical motor curve is, and you've boosted the voltage which should give you more torque.

A possibility is that the motor has "broken down" / "lost sync" i.e. the frequency is much higher than the rpm - similar to a DOL motor starting - the torque + efficiency is way down, the current/heat is way up.

Somehow at 5000+rpm you re-synced and got the power you needed.

Can you measure the frequency of the drive/windings and compare it to the RPM? If the motor is in sync, for max torque I'd expect a the frequency to be linear at approx RPM/30 + 4Hz. I.E. 4 Hz at 0rpm, 166 Hz at 5000 rpm.

Can you stick a battery volt + ammeter + motor volt / amp/ frequency meter in the frame while you video the dyno run output screen. A video tells 25,000 words a second 

cheers,
Woody


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## Stiive (Nov 22, 2008)

peggus said:


> Well, a motor simply won't behave like your dyno curves show unless the controller is commanding it to, or the load isn't fully loading it. There must either be something wrong with the controller parameters, or, the dyno doesn't work right above 5000 RPM. Major makes a good point as always, given the manufacturers data you should not be able to get peak torque at 6000RPM without doubling the pack voltage, 2x288V.


You dont think it could be an issue with the wrong nominal frequency setting?



peggus said:


> If you instrument the motor, measure phase current and motor voltage, I think you'll find that the dyno is lying to you above 5000RPM.


Yeh, will try do this, but its a bit hard on the dyno with everything jumping about. I dont think the dyno is lying because there was a noticable increase of power of the car, unless the dyno became unloaded, but this dyno is used for the petrol car upto 12,000RPM so i dont understand why it would do this.


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## Stiive (Nov 22, 2008)

s2156945 said:


> +1 on etischer's comment.
> 
> Also the 190Nm is not way above what the published/theoretical motor curve is, and you've boosted the voltage which should give you more torque.


My thoughts excatly. Boosted voltage and current




s2156945 said:


> A possibility is that the motor has "broken down" / "lost sync" i.e. the frequency is much higher than the rpm - similar to a DOL motor starting - the torque + efficiency is way down, the current/heat is way up.
> 
> Somehow at 5000+rpm you re-synced and got the power you needed.


Similiar to what i thought with the v/f being wrong and then being adjusted closer to the proper settings during field weakening




s2156945 said:


> Can you stick a battery volt + ammeter + motor volt / amp/ frequency meter in the frame while you video the dyno run output screen. A video tells 25,000 words a second


Ill see what i can do  I have videos filming the output display screen from the controller which shows Voltage, Amps and RPM but i dont know if these can be trusted. The RPM on the dyno matches that from the controller.

Ill see if i can get a voltmeter on the DC bus, another on the line-to-line voltage, and the DC bus current. If i can get the monitor in there for comparison and RPM as well i will. I have CT's on the phase leads, but at the moment i dont really want CRO leads on them on the dyno cus theyl fall off, but ill look at extending their leads now


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## major (Apr 4, 2008)

Stiive said:


> My thoughts excatly. Boosted voltage and current


Sorry mate, that doesn't happen  

Motor phase current is always higher than DC current and phase voltage is always lower than DC voltage, using RMS of course.


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## peggus (Feb 18, 2008)

So presuming the dyno isn't wrong and the measured output power is correct then the controller must not be driving the motor right and the motor is wound for much lower voltage than the manufacturers data suggest, lower V/Hz that is.

The motor could be wound wrong, or connected in delta instead of wye, this would lead to roughly half the back EMF for a given torque, but also half the torque per amp.

The controller claims to be a vector control according to the marketing pamphlet. Usually that means field oriented control, in which case the controller will have an internal model of the motor which it uses to estimate the position of the rotor flux so that it knows how to apply the stator flux to maximize torque. This model contains parameters for things like inductance, mutual inductance, rotor resistance, inertia etc, etc.

Obviously, if the motor is not what the controller thinks it is, or someone went and added external inductors, then the output of this model will be wrong, the stator flux will be applied at the wrong angle and torque will suffer.

Why it suddenly improves above 5000RPM is a bit of a mystery to me.

The pamphlet also claims that the controller has autotune, have you tried that?

If the only parameters you can control are V/Hz, then I'd try cutting it in half, or 1.73, and see what happens.

Somone mentioned loosing sync, which is interesting, the torque curve looks very much like a torque/slip curve, which would suggest the controller output frequency is constant regardless of motor speed. Is the speed feedback working right? Is the controller somehow configured to run open loop at a fixed speed set point?


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## peggus (Feb 18, 2008)

Are you by any chance running the controller in open loop V/Hz mode with the throttle input controlling the Hz, jamming the throttle to the floor and using the dyno to regulate the speed?


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## major (Apr 4, 2008)

peggus said:


> or someone went and added external inductors,


Hey peg,

I think I saw where they did add inductors. Remember a comment about them getting hot 

major


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## Stiive (Nov 22, 2008)

major said:


> Sorry mate, that doesn't happen
> 
> Motor phase current is always higher than DC current and phase voltage is always lower than DC voltage, using RMS of course.



By that I meant increased motor nominal current (200A rather than the stated 105A). Also the DC bus voltage is 300v nominal so giving increased voltage to the motor is not hard. But I understand what you mean.


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## Stiive (Nov 22, 2008)

peggus said:


> Are you by any chance running the controller in open loop V/Hz mode with the throttle input controlling the Hz, jamming the throttle to the floor and using the dyno to regulate the speed?


We are running the controller in what we think is normal FOC vector control where the accelerator pot is the torque reference. We then bring the motor to about 500RPM and then floor it. The dyno does however control the speed and rate of acceleration. We tried different acceleration value to see if it changed te shape of the graph at all, but it didn't seem to


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## Stiive (Nov 22, 2008)

major said:


> Hey peg,
> 
> I think I saw where they did add inductors. Remember a comment about them getting hot
> 
> major


Yes we have series inductors on the phase tails which we are hoping to remove. We had put them in for stability as we were seeing a noisy PWM output from the controller. We also had random issues of blowing IGBTs when running the auto-tune test, so we havnt run one in awhile, though the last auto tune was done with the inductors so it knows they're there.


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## peggus (Feb 18, 2008)

Stiive said:


> We are running the controller in what we think is normal FOC vector control where the accelerator pot is the torque reference. We then bring the motor to about 500RPM and then floor it. The dyno does however control the speed and rate of acceleration. We tried different acceleration value to see if it changed te shape of the graph at all, but it didn't seem to


Good, that is what you should be doing. However can you verify that the controllers fundamental frequency is changing proportional to the speed. A current probe on one of the phase leads and a scope should show you the waveform and frequency nicely. 

The reason I'm going down this path is because your torque curve looks very much like this:









Which is what you get when you hook up a induction motor to an AC source with fixed frequency.


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## Stiive (Nov 22, 2008)

peggus said:


> So presuming the dyno isn't wrong and the measured output power is correct then the controller must not be driving the motor right and the motor is wound for much lower voltage than the manufacturers data suggest, lower V/Hz that is.


It seems that way, when the motor is given the v/hz suggested by the manufacturer, it squeels from saturation. I think possibly the boost voltage (initial voltage at 0Hz) could be wrong. Possibly its set as a % of the nominal voltage and is too high when we increase the voltage. I cannot however find this setting anywhere!



peggus said:


> The motor could be wound wrong, or connected in delta instead of wye, this would lead to roughly half the back EMF for a given torque, but also half the torque per amp.


We also thought this awhile back, but the motor manufacturer has told us it is in star config.



peggus said:


> The controller claims to be a vector control according to the marketing pamphlet. Usually that means field oriented control, in which case the controller will have an internal model of the motor which it uses to estimate the position of the rotor flux so that it knows how to apply the stator flux to maximize torque. This model contains parameters for things like inductance, mutual inductance, rotor resistance, inertia etc, etc.
> 
> Obviously, if the motor is not what the controller thinks it is, or someone went and added external inductors, then the output of this model will be wrong, the stator flux will be applied at the wrong angle and torque will suffer.


We have added inductors, but have preformed the auto-tune test with these inductors installed. At the reduced v/hz though otherwise the test fails and blows an IGBT



peggus said:


> Why it suddenly improves above 5000RPM is a bit of a mystery to me.


Yes, definetly is something to do with filed weakening tho, because we have since set the frequency to 120Hz and the same thing happens at 3,600RPM



peggus said:


> The pamphlet also claims that the controller has autotune, have you tried that?


Yes, however it can only be done at a reduced v/hz otherwise we blow fuses and IGBTs :S



peggus said:


> If the only parameters you can control are V/Hz, then I'd try cutting it in half, or 1.73, and see what happens.


Do you mean divide the v/hz ratio by 1.73, or try a ratio of 1.73? We have been using half the rated v/hz ratio of 0.6 rather than the suggested 1.2. When running with 120Hz however we dont want to decrease the voltage too low.




peggus said:


> Somone mentioned loosing sync, which is interesting, the torque curve looks very much like a torque/slip curve, which would suggest the controller output frequency is constant regardless of motor speed. Is the speed feedback working right? Is the controller somehow configured to run open loop at a fixed speed set point?


No idea if you can turn off closed loop and run in open loop, however i dont see why you'd want to. Ill hook the car back up to the CRO and see if i can see the frequency increasing


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## Stiive (Nov 22, 2008)

peggus said:


> Good, that is what you should be doing. However can you verify that the controllers fundamental frequency is changing proportional to the speed. A current probe on one of the phase leads and a scope should show you the waveform and frequency nicely.
> 
> The reason I'm going down this path is because your torque curve looks very much like this:
> 
> ...


Thanks for that, the curve does interestingly look very similiar. We have CTs on each of the phase tails which we normally have a CRO hooked up to, however we forgot the extension leads we made for the dyno last time and therefore didnt use them. I will definetly have to suss this out!


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## JRP3 (Mar 7, 2008)

major said:


> Motor phase current is always higher than DC current


Even at full power? Because I used an AC clamp on meter with peak hold on one of my motor phases and peak motor current was within about 10 amps of peak battery current.


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## major (Apr 4, 2008)

JRP3 said:


> Even at full power? Because I used an AC clamp on meter with peak hold on one of my motor phases and peak motor current was within about 10 amps of peak battery current.


Hi JR,

I've seen the currents get really close above base RPM but don't recall ever seeing them cross. I was speaking from experience, not theory here. Are you saying your DC was higher than the AC phase current? Or just 10A lower? And what? 10A out of 500? If so, I'd call it about the same 

What do you have? The AC20 system? I had been running some tests on an AC15 and it conformed to what I said.

Sorry Stiive, don't want to hijack your thread 

major


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## JRP3 (Mar 7, 2008)

I have the AC31, 550 amp max controller, saw 550 battery amps, I think it was around 535 motor phase amps if I remember, so close enough to call it the same, but in conflict with your statement that motor amps are always higher than battery amps.


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## major (Apr 4, 2008)

JRP3 said:


> I have the AC31, 550 amp max controller, saw 550 battery amps, I think it was around 535 motor phase amps if I remember, so close enough to call it the same, but in conflict with your statement that motor amps are always higher than battery amps.


2.7%, if you remember correctly  Likely within the margin of error for 2 current measurements in a noisy environment. Maybe I should have said "always higher or approximately equal to".


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## Stiive (Nov 22, 2008)

Here's some of the reasons why we put in the inductors. This is the current and PWM before we put inline inductors: 

Current 
























Voltage PWM 

















After inductors: 










Here is some more recent testing on the dyno. We were able to get the rated power out of the motor (60kW), and even get pretty well perfect field weakening! However, the torque still rapidly increases just before synchronus speed to get the power, this is unacceptable. To get the acceleration we need, we really want the constant 190NM as shown in the manufacturers torque/speed graph. Its pretty stupid to be driving along at 60km/h with 100Nm or torque then all of a sudden within a space of 500RPM be getting 165Nm, on a 300kg car you'll loose the backend! 
Its interesting that the torque had a separate peak at 1200RPM before dropping off again. I don't think the dyno is lying because the acceleration is extremely slow, and the petrol car with far less torque in that area accelerates much quicker and smoother. Still need to find the voltage boost setting to see if that fixes anything! 









To produce this graph we used the following settings: 
Nominal current= 212A 
Nominal Voltage = 105V 
Max Voltage = 105V (100%) 
Nominal Frequency = 120Hz 

We also got a very similiar result with 
Nominal current= 212A 
Nominal Voltage = 72V 
Max Voltage = 108V (150%) 
Nominal Frequency = 120Hz 









Notice the decrease of nominal frquency from 175Hz to 120Hz, thats why the motor peaks earlier. 
We are also still flooding the motor with current (rated at 105A) to get this power, which is causing it to heat up very quickly. 

Also the blue run in the above dyno pic is when the voltage max was set at 100% (72V). Interesting to see the effects the voltage max has on the torque, it always seems to make it peak earlier

Sorry, still no CRO readings while on the dyno, hopefully tomorrow night. 

Stefan


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## Stiive (Nov 22, 2008)

Did some no load tests today, the frequency is definetly changing w.r.t throttle/speed, as does the phase voltage.

Probably worth noting, even though it was a no-load test, we still saw full voltage and close to full amp draw on the phase tails. There isnt much current draw on the DC bus however so it must be a very small PF.

Going to try removing the inductors tomorrow before we run on the dyno again.


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## steven4601 (Nov 11, 2010)

Very informative , hope you solve the torque curve soon. 

My limited experience with vfd's makes me think your program is mostly slip related. The lower rpms there is too much slip. a lower max slip may help...


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## Stiive (Nov 22, 2008)

Footage of the car on the dyno if anyones interested

http://www.youtube.com/watch?v=PuhiSfeETfw


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## steven4601 (Nov 11, 2010)

Something apears to be wrong there.

The current waveform @ 21 seconds appear to be saw-tooth in shape!?
Current going in, but no energy/current is stored / recirculated? Current should be atleast triangular or even better sinusoidal, but it appears the IGBT's are barely using PWM modulation. 

A little further in time 24 seconds, the shape starts to round and then my next question arises, why such a massive dead-time is used for the output!? 

@ 30 seconds it looks really good, that is when torque starts to be produced? I have no audio here atm.


My question,
Is that scope using real current probes (atleast 100kHz bandwidth) ?
These saw-tooth shapes are a strong indication something is wrong. 

My expectation is that a sine wave should also be present at very low rpm's.

//Steven


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## steven4601 (Nov 11, 2010)

Just something I noticed, in the video you post various 'nominal frequencies but also at different rpm's)

I could be wrong, but with the principle nominal frequency is a relationship to the rpms.
RPM & Motor Voltage is how many volts at which rpm is needed. This is somewhat a linear curve with an initial offset to flux the motor. 
Nominal frequency is the frequency needed to get the motor to its rated RPM.
Volt/Hz curve is derrived from these values, PI loops in the drive try to find a way to regulate the small irregularity along the way from 0 to max rpm.


IF the motor plate states 100hz @ 1000 rpm, it could also have used written 200hz @ 2000 rpms. *ignoring the required motor voltage in this explanation* This ratio is the same. If this value is too far off it will start to use the PI loops beyond their intended use. These PI loops can easely running at their saturation limits until you reach a point where field weakening should occur. . .

Hope my ramblings help.


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## Stiive (Nov 22, 2008)

steven4601 said:


> IF the motor plate states 100hz @ 1000 rpm, it could also have used written 200hz @ 2000 rpms. *ignoring the required motor voltage in this explanation* This ratio is the same. If this value is too far off it will start to use the PI loops beyond their intended use. These PI loops can easely running at their saturation limits until you reach a point where field weakening should occur. . .
> 
> Hope my ramblings help.


Hi Steven,
Thanks for your replies, we are only setting the nominal frequency value, there is no input value for nominal speed.. I was simply writing the RPM value the frequency correlates to for a 4-pole motor so other people wouldnt have to do the calculation.

The motor had specified a 175Hz nominal frequency which means its nominal speed would be 5,250RPM, however we wanted the curve to be more like the one they supplied where the nominal speed was 3,600RPM, so we set the nominal frequency to 120Hz. Hope this makes sense.

Stefan


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## Stiive (Nov 22, 2008)

steven4601 said:


> The current waveform @ 21 seconds appear to be saw-tooth in shape!?
> Current going in, but no energy/current is stored / recirculated? Current should be atleast triangular or even better sinusoidal, but it appears the IGBT's are barely using PWM modulation.
> 
> A little further in time 24 seconds, the shape starts to round and then my next question arises, why such a massive dead-time is used for the output!?


Yes, we've always been extremely concerned about the saw tooth. It seems its only doing part of a sine wave. Perhaps it needs to lower the duty cycle too much to acheive the low voltages from our big 340V pack. But it seems to get a linear increase on the saw-tooth before it cuts out, it just cant finish it off. 
However it must be doing alright because cogging isnt really noticable after about 3-4Hz, which is acceptable; But the drivetrain does sound a bit rough below about 2000RPM (not sure if thats due to the drive-train or power-train)



steven4601 said:


> My question,
> Is that scope using real current probes (atleast 100kHz bandwidth) ?
> 
> //Steven


I believe so, I will have to check next time i'm at uni; They're properlly sheilded but are quite an ancient model that went with our old CRT analogue CRO.


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## Stiive (Nov 22, 2008)

Heres a snapshot of the sawtooth current waveform from 0.43 seconds, you can see the pulses from the pwm. 
At 44 seconds it also seems you can see a sinusoidal wave on one of the phases.











Also, the true-RMS multimeter on the left is reading the frequency of phase-phase, what do you think its picking up? The drive frequency was set to 5kHz, yet this value is all over the place. The maximum freq of the drive is 16kHz according to the manual


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## steven4601 (Nov 11, 2010)

multimeters are no frequency meters by default. (in a sense it usually has less than ideal hardware for frequency measurement)

Expecting this meter bandwidth is low, it can only measure a few kilohertz or less. Some can measure 100's of khz, but id be worried with those specs.

What that meter is likely displaying if set to Hz is the phase-frequency. Ignoring all PWM frequencies.


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## peggus (Feb 18, 2008)

Wow, yes there is definitely something funky going on with your inverter. It's like it is hitting some current limit every cycle and shutting down the pwm until the start of the next AC cycle. It would certainly explain why you don't have good torque at low RPMs. 

Time for crazy ideas... since you get peak torque at and above whatever you're setting the nominal freq to, what happens if you set it to 10Hz?? Likely I'm missing something here but wth.....

I presume there is no way to get the manufacturer to come out and prove to you that their product can do what they claim it can do?


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## peggus (Feb 18, 2008)

To further investigate I would set up the scope to trigger off of the falling edge of one of your phases, set the trigger level above 0 and try to capture that last pwm cycle just before the triangle drops off the cliff, and zoom in so you can see any rapid transients. Run the motor at a constant low speed. I'd be most curious to see what happens on that last cycle.



By the way, at what current does your inductors saturate?


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## steven4601 (Nov 11, 2010)

CAREFULL there!

10Hz nominal frequency can make the V/Hz curve way out of 'whack'.

It is very suspicious no default motor RPM can be given. Everything has to be correlated from their nominal RPM then........


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## Stiive (Nov 22, 2008)

steven4601 said:


> What that meter is likely displaying if set to Hz is the phase-frequency. Ignoring all PWM frequencies.


The phase frequency should never get above about 200Hz as thats the motors max speed, it should never be 30kHz for example as shown in the above pic


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## Stiive (Nov 22, 2008)

peggus said:


> Wow, yes there is definitely something funky going on with your inverter. It's like it is hitting some current limit every cycle and shutting down the pwm until the start of the next AC cycle. It would certainly explain why you don't have good torque at low RPMs.
> 
> Time for crazy ideas... since you get peak torque at and above whatever you're setting the nominal freq to, what happens if you set it to 10Hz?? Likely I'm missing something here but wth.....
> 
> I presume there is no way to get the manufacturer to come out and prove to you that their product can do what they claim it can do?


You can see in one of the tests we decreased the nominal freq to 80Hz, however we didnt auto-tune it before doing the tests so it didnt make the torque kick in any earlier. We later did another auto-tune and as expected it made the torque kick in at 2,400 RPM, but with reduced power as we had to reduce the voltage accordingly to keep the proper V/Hz ratio


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## peggus (Feb 18, 2008)

well, drop the volts too.



steven4601 said:


> CAREFULL there!
> 
> 10Hz nominal frequency can make the V/Hz curve way out of 'whack'.
> 
> It is very suspicious no default motor RPM can be given. Everything has to be correlated from their nominal RPM then........


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## Stiive (Nov 22, 2008)

peggus said:


> To further investigate I would set up the scope to trigger off of the falling edge of one of your phases, set the trigger level above 0 and try to capture that last pwm cycle just before the triangle drops off the cliff, and zoom in so you can see any rapid transients. Run the motor at a constant low speed. I'd be most curious to see what happens on that last cycle.


Unfortunately we can't do any testing at the moment, will release details soon



peggus said:


> By the way, at what current does your inductors saturate?


No idea, these were custom wound by a friend, I am told they're of very small inductance (mH i think)


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## peggus (Feb 18, 2008)

Stiive said:


> You can see in one of the tests we decreased the nominal freq to 80Hz, however we didnt auto-tune it before doing the tests so it didnt make the torque kick in any earlier. We later did another auto-tune and as expected it made the torque kick in at 2,400 RPM, but with reduced power as we had to reduce the voltage accordingly to keep the proper V/Hz ratio


Ah, reduced power and reduced torque, or just reduced power?


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## Stiive (Nov 22, 2008)

peggus said:


> Ah, reduced power and reduced torque, or just reduced power?


Just power, we were still able to force the current in so it still peaked at about 180Nm. It didnt really bother us, apart from the fact that it got this torque boost at corner exit speed in our single reduction. 

Would be fun coming out of a corner flooring it cus your only getting 90Nm of torque and then it instantaniously doubles...


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## Stiive (Nov 22, 2008)

NB: obviously the power was less too because the torque happened earlier and the torque dies off afterwards due to field weakening


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## steven4601 (Nov 11, 2010)

Sorry I missed the fact the meter was showing 30khz instead of 30hz... That makes it a useless meter for this measurement. Reasons of caution using multimeters I already put out in previous posts. You need scopes, preferably modern fast ones that have some way of aliasing samples like an analog scope can to visualize what is going on. 

My concerns would be figuring out why the motor is fluxed so horribly at low speed. I would stop all dyno runs until you get 190nm (or close) stall torque. Measure with a scale and a lever or something clever.


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