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Everything I've Been Able To Learn About The Model 3 Motor: Welcome to the Machine

Compared to a typical PM motor, say in the the Bolt, I wonder what the relative fraction of rare earth metals are.
I'm also wondering if the new design widens the range of which rare earth magnets can be used.
Bolt is a PM machine using switched reluctance effects, similar to what is being claimed of the Model 3 machine. BMW i3 did it before the both of them. This is nothing new.

Here's a link about the BMW: BMW’s hybrid motor design seeks to deliver high efficiency and power density with lower rare earth use
 
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Bolt is a PM machine using switched reluctance effects, similar to what is being claimed of the Model 3 machine. BMW i3 did it before the both of them. This is nothing new.

Here's a link about the BMW: BMW’s hybrid motor design seeks to deliver high efficiency and power density with lower rare earth use

These are hybrid synchronous reluctance machines, or PM assisted synchronous reluctance machines. The article is claiming that Model 3 uses a hybrid SWITCHED reluctance machine. SRMs achieve higher torque densities thatn SynRMs but usually show high levels of torque ripple and noise/vibration. The speed and accuracy of position measurement and control needed to overcome these is why SRMs have not really found much commercial use despite being theoretically excellent.
IF the article is correct and this is indeed a PMSRM rather than a PMSynRM, this would indeed be novel and indicate that Tesla have made significant strides in SRM control.
 
These are hybrid synchronous reluctance machines, or PM assisted synchronous reluctance machines. The article is claiming that Model 3 uses a hybrid SWITCHED reluctance machine. SRMs achieve higher torque densities thatn SynRMs but usually show high levels of torque ripple and noise/vibration. The speed and accuracy of position measurement and control needed to overcome these is why SRMs have not really found much commercial use despite being theoretically excellent.
IF the article is correct and this is indeed a PMSRM rather than a PMSynRM, this would indeed be novel and indicate that Tesla have made significant strides in SRM control.

I do think this is still a PMSynRM. In the PMSRM the permanent magnets just reduce cogging torque and don't actively increase torque as they do in a PMSynRM and wile 30% higher torque densities sound great, a SRM has a lot lower torque, than an IPM. The PMSRMs are also really hard to produce in volume, compared to an IPM, or PMSynRM, since the magnets are very close to the rotor and PMs are very brittle.

IMO this is "just" a PMSynRM, they are cheap to produce and have great power and torque densities. The PMSRM is a neat concept, but probably only for doctorates that want an easy to manufacture motor (in low volumes) they can study (as SRMs have always been the best motor for doctorates for that reason). Just glue some PMs to the project of the former doctorate and you are good to go.
 
I do think this is still a PMSynRM. In the PMSRM the permanent magnets just reduce cogging torque and don't actively increase torque as they do in a PMSynRM and wile 30% higher torque densities sound great, a SRM has a lot lower torque, than an IPM. The PMSRMs are also really hard to produce in volume, compared to an IPM, or PMSynRM, since the magnets are very close to the rotor and PMs are very brittle.

IMO this is "just" a PMSynRM, they are cheap to produce and have great power and torque densities. The PMSRM is a neat concept, but probably only for doctorates that want an easy to manufacture motor (in low volumes) they can study (as SRMs have always been the best motor for doctorates for that reason). Just glue some PMs to the project of the former doctorate and you are good to go.

Agreed on every count. The difference between PMSRM and PMSynRM seems to have been lost in the CleanTechnica article. Haven't watched Ingineerix' video, but it would be interesting to see if he is more specific. Seeing the end windings should be enough to distinguish the two, right? As the PMSRM would have concentrated windings vs distributed for the PMSynRM.
 
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OP, are you the author of the CleanTechnica article? If so, very nice article. Really interesting and informing. I sent it to my dad who's an engineer and he loved it too.

Guilty. Appreciate the kudos. And, as you can see from the studied comments in this thread, this rabbit hole goes much deeper than the article. Clearly, understanding these motors... and the Model 3's specific implementation... is a process, not an event.
 
@Gerasimental and @R.S great comments.

The difference between PMSRM and PMSynRM seems to have been lost in the CleanTechnica article.

Exactly. It got lost because in researching the piece I didn't stumble across the distinction between the two. I am not an engineer, and have been simply playing journalist as I try to understand this fascinating tech. What I have not gotten down yet is the difference between PMSRM and PMSynRM machines. Virtually all the references I came across discussed the Switched Reluctance Machine, and there's even been an assertion that the "S" in "SRM" can mean either "Switched" or Synchronous", as though it's always referring to the same design.

If either of you care to describe the differences between the two designs I (and I'm sure others) would love to hear. For me personally I have yet to understand how a motor can be synchronous when it seems the electromagnets in the stator are always a bit ahead of the rotor... pulling it along. ;>
 
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BTW - I quoted Ingineerix in the article where he simply stated “Switched Reluctance motor, using permanent magnets.” Ingineerix went on to say, “Tesla calls it a PMSRM, Permanent Magnet Switched Reluctance Motor. It’s a new type, and very hard to get right, but Tesla did it!” He didn't go any further.
 

mongo

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May 3, 2017
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@Gerasimental and @R.S great comments.



Exactly. It got lost because in researching the piece I didn't stumble across the distinction between the two. I am not an engineer, and have been simply playing journalist as I try to understand this fascinating tech. What I have not gotten down yet is the difference between PMSRM and PMSynRM machines. Virtually all the references I came across discussed the Switched Reluctance Machine, and there's even been an assertion that the "S" in "SRM" can mean either "Switched" or Synchronous", as though it's always referring to the same design.

If either of you care to describe the differences between the two designs I (and I'm sure others) would love to hear. For me personally I have yet to understand how a motor can be synchronous when it seems the electromagnets in the stator are always a bit ahead of the rotor... pulling it along. ;>


Synchronous meaning the motor/ rotor spins at the same speed as the exciting stator field. The offset/ phase angle between the rotor and the stator field may vary based on torque but they rotate at the same speed.

Contrasted to that is an AC induction motor where the rotor spins at a different speed than the stator field due to the slip factor which generates torque. More loaded: rotor turns slower, less load: rotor approaches synchonous speed.
 
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Agreed on every count. The difference between PMSRM and PMSynRM seems to have been lost in the CleanTechnica article. Haven't watched Ingineerix' video, but it would be interesting to see if he is more specific. Seeing the end windings should be enough to distinguish the two, right? As the PMSRM would have concentrated windings vs distributed for the PMSynRM.

You can still build a PMSynRM with concentrated windings, but if they are distributed, it's definitely no PMSRM.

From everything we know right now, Tesla calling it an IPM on the window sticker, to the superior thermal capability on the track, I am pretty sure it's an IPM, or PMSynRM.

This just exists because ingineerix called it a SRM (he also called it a BLDC) and then said it has permanent magnets (in the rotor). Someone then researched the PMSRM, found out that nobody uses it and that basically means "Tesla is way ahead".

So the mistake fitted the narrative of Tesla being the only ones that understand electric motors (I remember the times when I argued that the Model 3 will probably have an IPM, because better, to only get lectured about: "the superiority of an AC induction engine and the so called invertor") So Tesla, again, going for something weird sounded interesting enough to go around the interwebs.
 
@Gerasimental and @R.S great comments.



Exactly. It got lost because in researching the piece I didn't stumble across the distinction between the two. I am not an engineer, and have been simply playing journalist as I try to understand this fascinating tech. What I have not gotten down yet is the difference between PMSRM and PMSynRM machines. Virtually all the references I came across discussed the Switched Reluctance Machine, and there's even been an assertion that the "S" in "SRM" can mean either "Switched" or Synchronous", as though it's always referring to the same design.

If either of you care to describe the differences between the two designs I (and I'm sure others) would love to hear. For me personally I have yet to understand how a motor can be synchronous when it seems the electromagnets in the stator are always a bit ahead of the rotor... pulling it along. ;>
Broken down it's as follows:

A regular synchronous PM motor has permanent magnets somewhere in or on the rotor, those usually form a magnetic field that induces a sine wave into the stator windings. If the stator windings carry a current themselves, the rotor moves along at the same speed as the magnetic field of the stator. Imagine a magnetic compass needle following another magnet around.

The SRM uses the reluctance, so basically the rotor iron magnetizes. But other than with a synchronous machine, only one pole is excited and the salient poles in the core move until they are under that pole. Then the next pole gets excited and it makes another step.

A PMSynRM also uses reluctance, iron being magnetic, but also magnets and, other than the SRM, it moves continuously. The magnets are in the rotor and increase the magnetic flux.

A PMSRM again does those step movements and has the magnets on the stator.

A BLDC also does steps like the PMSRM, but has magnets on the rotor.

A big difference is the torque ripple and the duty cycle. In the BLDC, SRM and PMSRM the currents are rectangular, in the IPM, or PMSynRM they are modulated sine waves. Additionally in the SRM the currents through the windings don't change direction. So the effective current (root mean square) in the IPM windings is 1/sqrt(2) = 0.7, in the BLDC it's 0.66 and in the SRM it's either 0.33, or 0.5.

So with the same maximum current per winding, a sine waveform is the one with the most torque.

And since especially at high speeds, the rectangular wave form can't be done anymore, since the inverter is at it's voltage limit, the torque ripples increase.
 

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