What Motor(s) will the Cybertruck use?

[Momo]

Since Model 3 uses both an induction and reluctance it's a good guess that the dual motor CT will be similar set up. With the single motor CT being an induction? Does that mean the 3 motor uses 2 reluctance motors? Or do we think the 3 motor is plaid with some other setup?

I'm not versed in motor mechanics. Can you explain the difference between the Permanent magnet motor Lucid Air will use and why the chief engineer touts it as a better motor than what Tesla has.

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[Dids]

I'm not versed in motor mechanics. Can you explain the difference between the Permanent magnet motor Lucid Air will use and why the chief engineer touts it as a better motor than what Tesla has.

If I'm correct they will be using Permanent Magnet Synchronise Motors in Lucid. Synch motors use a AC frequency modulation to drive they motor, as the motor spins faster the AC frequency increases. People were saying that Tesla was using switched permanent magnet motors which would have made the driver a pulse width modulation. PWM is a DC technology. Sandy Munro said it's not switched. It's synch. So then I think Tesla is the same as Lucid for the permanent magnet motor. But Tesla also uses induction motors. Induction motors generally have better top end efficiency then a PM motor...

 

[ajdelange]

He touts it as better than Tesla because it is his company's motor. Why he thinks it is better I do not know. Did he say? What I'm getting at is that if you say yours is better than mine my first question is "What's your criterion for good?" Motor technology is, at this point, a fine art and a given motor may be better than another in one respect and worse in another. For example, the Tesla PM motors are more efficient than their own induction motors but the induction motors deliver more torque at low speed. "In what way is your motor better than Tesla's?" is a question that can best be answered by the guy that made the claim.

In general a PM motor is better than an induction one in that as it has no copper in the rotor there are no copper losses (motor is more efficient) and as the field direction in the rotor does not reverse there are no hysteresis losses either. The induction motor is better in its torque characteristics. But Tesla has a PM motor too.

 

[Momo]

If I'm correct they will be using Permanent Magnet Synchronise Motors in Lucid. Synch motors use a AC frequency modulation to drive they motor, as the motor spins faster the AC frequency increases. People were saying that Tesla was using switched permanent magnet motors which would have made the driver a pulse width modulation. PWM is a DC technology. Sandy Munro said it's not switched. It's synch. So then I think Tesla is the same as Lucid for the permanent magnet motor. But Tesla also uses induction motors. Induction motors generally have better top end efficiency then a PM motor...

Nice! Thanks a lot for the knowledge shared.

 

[ajdelange]

Most manufacturers seem to be leaning towards PM motors because of the efficiency advantage which leads to more range on a given sized battery. Permanent magnet motors are synchronous meaning that their rotors turn at the same speed as the rotating magnetic field produced in the stator (outer, fixed part of the motor) by the electronics. The other type of motor used in some BEV is the induction motor. It too has a rotating magnetic field generated by the vehicle's electronics but in an induction motor the stator field is made to rotate at a rate slightly greater (motoring) or less (regen) than the rotor. This relative speed induces (hence the name) electric current in the rotor and that current gives rise to a magnetic field which interacts with the stator field to produce the torque. No slip (speed difference), no induced current, no rotor field, no torque. In the PM motor the magnets provide the (constant) rotor field which interacts with the stator field to produce the torque. Obviously the rotor speed is proportional to vehicle speed with the proportionality depending on the tire radius and gearing ratio. For the rest of the post I'll use "rotor/wheel speed" to emphasize the relation ship between the rotor speed and how fast the car is going.

Thus both the IM and PM motors are AC machines. Both produce torque by means of a rotating magnetic field generated by PWM (pulse width modulation) of DC from the battery. In both the field rotation rate is set to be close to the desired rotor/wheel speed and in both the torque can be modulated by speeding up or slowing down the field rotation rate. If you want a car with an IM to go faster you increase torque by speeding up the field rotation rate (increase slip). As the vehicle accelerates you must keep increasing the field rotation rate to maintain the slip if you want to increase speed further. When the desired speed is reached you stop increasing field rate but not that it must be maintained at a rate faster than the rotor/wheel rate in order to produce the torque necessary to overcome drag, rolling resistance etc.

If you want to speed up a vehicle with a PM you do the same thing initially i.e. increase the field rotation rate so that it gets ahead of the rotor. The increased angle between them produces more torque so that the vehicle speeds up which, of course, allows the rotor to catch up so that here too one must continue increasing the field speed until the desired vehicle speed had been reached. At that point you trim the field speed to get the relative angle between rotor and stator fields to be the angle that produces the necessary torque to maintain that speed and then hold the field speed fixed. It will be equal to (synchronous with) the rotor/wheel speed

With PWM the DC battery current is switched to run through the stator coils first in one direction and then the other. The net current through the coil depends of the relative length of time the current flowed in each direction. The "width" here refers to the fraction of the switching cycle in one direction. Thus if the + direction switch is on for 100 % of the cycle the net current flow is maximum in the + direction. If the + switch is on for 50% of the cycle this implies that the - switch is on for the other half and current flows in one direction half the time and the net current flow is 0. And if the + direction switch is on 0% of the time the - direction one has to be on 100% of the time and the current flow is maximum in the reverse direction. Thus by modulating the width of the + direction I can set current to any level less than the maximum in either direction.

The PWM cycle is short (20's of microseconds). The width chosen for each cycle is such that the output current (or actually voltage) waveform is a close approximation to a sine wave whose frequency corresponds to the required rotation rate of the motor's stator field. The frequency of these sine waves is much less than that of the PWM cycles i.e. 10's of milliseconds.

I've given a high level description here of some of the major differences between how IM and PM (synchronous) motors are controlled. There is much more to it than just slip (IM) or load angle (PM) control. Oviously the PWM scheme allows the frequency of the voltage waveform to be set by the controller but its amplitude and phase relative to the rotor position can also be controlled and this is done using DSP (Digital SIgnal Processing) techniques. Also note that I do not claim to be describing what Tesla is doing but rather what it is very probable they are doing given the state of the art.

 

[TruckElectric]

Update:

I originally posted that Tesla doesn't publish their motor ratings. I was going on what I had read somewhere and at the time it may have been correct.

Well, after snooping around in Tesla's owners manuals I found something interesting.


In the model 3 owners manual it does not list the motor at all; although in the index it does list a motor specifications and page number to find it but it's not there.

The model Y owners manual does list the motor(s) under Specifcations: Subsytems

Rear motor: AC permanent magnet synchronous motor, liquid-cooled, with variable frequency drive. Front motor: AC induction motor, liquid-cooled, with variable frequency drive.


The model S owners manual gives even more information.

Front Motor AC induction motor, liquid-cooled, with variable frequency drive
Rear Motor AC permanent magnet synchronous motor, liquid-cooled, with variable frequency drive
Nominal Voltage 320 Volts

Maximun Motor Power for The Performance

Front motor 205 kW Rear motor 375 kW

Maximum Motor Torque

Front motor 420 Nm Rear motor 720 Nm



I didn't bother looking up the Model X


Just remember that the original Model S only had Induction motors. The inclusion of the PMSM is recent. It came after the Model 3 which had a new motor(PMSM) not included in the Model S and Model X.

 

[ajdelange]

For the X

Front Motor	AC permanent magnet synchronous motor, liquid-cooled, with variable frequency drive
Rear Motor	AC induction motor, liquid-cooled, with variable frequency drive
Nominal Voltage	320 volts

Strange that the positions of the induction and PM motors are reversed in S and X!

If the photo at the beginning of the thread represents the motors in these vehicles it clearly is an IPMSM/PMASRM

 

[TruckElectric]

For the X

Front Motor	AC permanent magnet synchronous motor, liquid-cooled, with variable frequency drive
Rear Motor	AC induction motor, liquid-cooled, with variable frequency drive
Nominal Voltage	320 volts

Strange that the positions of the induction and PM motors are reversed in S and X!

If the photo at the beginning of the thread represents the motors in these vehicles it clearly is an IPMSM/PMASRM

Thanks for the diagram showing Taxonomy of AC motors.


Basically I was going on what I had read and then deduction about the PMSM and PMSRM.

There were many what seemed to be knowledgeable comments about the Model 3 motor and there was disagreement about whether it was switched or synchronous. Even Jack Rickard and YTuber Ingineerix believed it to be a switched motor. Also an article in CleanTechnica was sure it was a switched motor CleanTechnica

But I found that pic from a teardown of a Model 3 motor and knew then it wasn't a switched motor.

 

[ajdelange]

It is pretty clear than Tesla would want to be using vector control and I think that would be hard to do with a switched design not to mention problems with harmonics, reduced efficiency, cogging etc. Plus they would want to continue to use the controllers they had developed for the induction motors.

 

[TruckElectric]

It is pretty clear than Tesla would want to be using vector control and I think that would be hard to do with a switched design not to mention problems with harmonics, reduced efficiency, cogging etc. Plus they would want to continue to use the controllers they had developed for the induction motors.

The addition of magnets in the rotor of the reluctance motor is to improve performance and it seems they achieved that.


It was assumed that Tesla had added magnets in the stator to reduce cogging - thus the switched reluctance motor, but the teardown of the motor proved that a wrong assumption.


I do believe this will be the motor(s) used in the CT. They seem to have done well in the Semi.

 

[ajdelange]

All these motors are "reluctance" motors to a certain extent and all, therefore, cog somewhat. If one adds permanent magnets to a reluctance motor then it becomes a PMSM but there will still be some reluctance torque because the reluctance of the material from which the magnets is made is very low so that the d and q inductances differ (if that means something to you, fine, if not don't worry about it). The problem seems to be what to call such a motor and, as my taxonomy diagram seems to suggest, depends on the path which the development of the motor followed. If one starts out building a PM motor he calls it a PMSM (even though it develops some reluctance torque) but if one starts with a reluctance motor and then adds magnets to pick up some magnetic torque he is more likely to call it a PMASRM.

When it was discovered that the 3 had a different type of motor it was announced by the self appointed experts on the fora that the motor was a "switched reluctance permanent magnet motor". Sandy Munroe did an autopsy on an early 3 motor and spoke of it in awe indicating that they didn't really know what sort of motor it was but that they thought the magnets gave it some unique properties especially since they appeared to be Hallbach arrays. Nonetheless it is clear from the images of rotor and stator in that video that the motor is an IPMSM

When all is said and done the real question is "What should we call this motor?". The answer is clearly that we should call it what Tesla calls it: A Permanent Magnet Synchronous Motor. If we want to add a little information we could augment that to Interior Permanent Magnet Synchronous Motor.

 

[TruckElectric]

When all is said and done the real question is "What should we call this motor?". The answer is clearly that we should call it what Tesla calls it: A Permanent Magnet Synchronous Motor. If we want to add a little information we could augment that to Interior Permanent Magnet Synchronous Motor.

I will call it a PMASRM since it is a reluctance motor. The diagram you posted is accurate. If you look at the Interior PM motor at the bottom it is connected to PM Assisted Reluctance.

Update: It is a PMSM not a PMASRM. If it was a PMASRM Tesla would have said so. They say it's a PMSM in their Owner's Manual.

Also interesting about that diagram. It includes a BLDC motor curiously since it says "Taxonomy of AC motors".

 

[ajdelange]

I will call it a PMASRM since it is a reluctance motor.

Except that it isn't really other than in the sense that all motors develop some reluctance torque. To call it a reluctance motor suggests that the majority of the torque it produces is reluctance torque and that's not the case here. Show the picture to a motor guy and ask him what it is. He will answer IPSM. And as Tesla calls it that I suggest you call it that too but you are free, of course, to call it whatever you like. It was erroneously called a reluctance motor in many of these fora for several months. It would be nice if people stopped doing that as it can only lead to propagating this misinformation.

The diagram you posted is accurate.

Given that it came from a textbook on motors and how much textbooks cost these days I would hope so!

If you look at the Interior PM motor at the bottom it is connected to PM Assisted Reluctance.

The problem seems to be what to call such a motor and, as my taxonomy diagram seems to suggest, depends on the path which the development of the motor followed. If one starts out building a PM motor he calls it a PMSM (even though it develops some reluctance torque) but if one starts with a reluctance motor and then adds magnets to pick up some magnetic torque he is more likely to call it a PMASRM.

That's why the two are connected. They are the same thing.

Also interesting about that diagram. It includes a BLDC motor curiously since it says "Taxonomy of AC motors".

Nothing curious about that. A brushless "DC motor" is clearly an AC motor with the only difference between it and a PMSM being trapezoidal vs sinusoidal EMF. This is indicated on the diagram.

 

[TruckElectric]

Except that it isn't really other than in the sense that all motors develop some reluctance torque. To call it a reluctance motor suggests that the majority of the torque it produces is reluctance torque and that's not the case here. Show the picture to a motor guy and ask him what it is. He will answer IPSM. And as Tesla calls it that I suggest you call it that too but you are free, of course, to call it whatever you like. It was erroneously called a reluctance motor in many of these fora for several months. It would be nice if people stopped doing that as it can only lead to propagating this misinformation.

Given that it came from a textbook on motors and how much textbooks cost these days I would hope so!

You are correct since Tesla does call their motor PMSM and so it shall be called.

I had in my mind that Tesla was trying to get away from using too much rare earth materials that are used in magnets that it made sense to use the PMASRM that uses less magnets.

 

[TruckElectric]

Show the picture to a motor guy and ask him what it is. He will answer IPSM.