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Old 15th July 2019, 09:45   #1
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Default Electric vehicles - Types of motors?

Let me open this post by saying I don't have much knowledge regarding various electric motors and their advantages or disadvantages for use in a electric vehicle.

Yesterday i was thinking why Hyundai couldn't give us a model with 64kWh battery and the lower powered 100kW motor of 39kWh model for an even better range than a 64kWh battery with 150kW motor could provide. Or is it possible to de-tune the 150kW PMSM motor in 64kWh Kona to 100kW or lower output which makes that large battery and low power motor variant totally redundant.

Proper and almost practical as a daily driver electric vehicles are now at our doorstep (Kona, Ather etc) and just like we used to discuss various internal combustion engine types i think it is time for us to start discussing electric motors.

What are the advantages and disadvantages of each type of electric motors
for use in a vehicle? For starters, which among the three types listed below is the better motor? Only Tesla seems to use an AC induction motor while the rest are going with permanent magnet types. Also doesn't the strength of a magnet reduce over time and in high heat conditions?
  • Tesla use a 3 phase 4 pole AC induction motor
  • Hyundai Kona, Leaf, Prius use Permanent Magnet AC Synchronous Motor (PMSM)
  • Ather scooterand old Prius use a brushless DC motor

Last edited by Zappo : 15th July 2019 at 12:07. Reason: Typo corrected
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Old 15th July 2019, 10:33   #2
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Default Re: Electric vehicles - Types of motors?

I think Tesla is moving away from induction motors to permanent magnet types. The cost is higher but efficient and mechanically smaller.

Variable frequency drives are being improved to control the permanent magnet types and might replace the induction motors.
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Old 15th July 2019, 10:47   #3
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Default Re: Electric vehicles - Types of motors?

A most appropriate thread. Thankyou for starting it. I am not an engineer and don't understand much about electric motors. I met a tech entrepreneur from California who said his firm is working on a motor that absorbs the EMF given out by a motor and feeds the energy back into the battery. I listened politely having no clue if this is possible or not and whether it is worthwhile even. Welcome any opinions from the experts.

Eventually improvements in motors and batteries will be needed to make EVs truly attractive.

Last edited by V.Narayan : 15th July 2019 at 10:48.
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Old 15th July 2019, 10:47   #4
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by Sankar View Post
[*]Tesla use a 3 phase 4 pole AC induction motor
I have read on other forums that the Tesla model 3 uses a switched reluctance interior permanent magnet motor. Some info here.

https://electrek.co/2018/02/27/tesla...-magnet-motor/

I think, recently Tesla switched model S and X to also use similar motors.
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Old 15th July 2019, 11:48   #5
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Default Re: Electric vehicles - Types of motors?

What would be the life of the permanent magnets?
And what precautions does one need to take to ensure their longevity?
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Old 15th July 2019, 11:50   #6
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Default Re: Electric vehicles - Types of motors?

We should all be thankful to the late Count Tesla for ac, since the Edison camp wanted all dc.

A lot of the disadvantage of dc motors is gone, since the advent of Rare Earth magnets (SmCo5 and its deritatives).Small in weight and very powerful. Only an ac motor will have a lower torque, so it is horses for courses.

I will not worry about the motor used.
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Old 15th July 2019, 11:56   #7
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Default Re: Electric vehicles - Types of motors?

PMSM and brushless dc motor are almost the same thing. They have small constructional differences but the physics is same.
Induction motor is an older technology that doesn’t require magnets. They are cheap and easy to make but have lower efficiency than PMSM and other motors which is why tesla is moving away from them.

Currently, switched reluctance motors are becoming more popular.Tesla has now switched to using this motor in the new models. The stepper motors used in 3d printers are an example of this kind of motor.

There is also a new technology called axial flux motors which have extremely high power density that are being developed for electric planes. However, I personally don’t see them coming to mainstream cars for a long time.

A good discussion thread on this topic:
https://electronics.stackexchange.co...ad-of-a-dc-one

Coming to the original question that you asked, the power of the motor doesn’t matter much when it comes to range. You see, motors are extremely good at taking what they need i.e. the amount of energy that a motor will demand from battery only depends on the load that its experiencing. And the only thing that determines load on the motor are the weight of the vehicle, vehicle speed and acceleration. You can put a million kW motor and it will still give you the same range if these 3 parameters are kept the same. So if you want to a better range, reduce the driving speed, acceleration and weight.

Last edited by LiCoO2 : 15th July 2019 at 12:02.
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Old 15th July 2019, 14:35   #8
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by srishiva View Post
I think Tesla is moving away from induction motors to permanent magnet types. The cost is higher but efficient and mechanically smaller.

Variable frequency drives are being improved to control the permanent magnet types and might replace the induction motors.
Quote:
Originally Posted by GutsyGibbon View Post
I have read on other forums that the Tesla model 3 uses a switched reluctance interior permanent magnet motor. Some info here.

https://electrek.co/2018/02/27/tesla...-magnet-motor/

I think, recently Tesla switched model S and X to also use similar motors.
This is good news because if Tesla Motors is going this route. So if its good for Tesla (considering their market acceptance) it should be good for the rest.


Quote:
Originally Posted by V.Narayan View Post
A most appropriate thread. Thankyou for starting it. I am not an engineer and don't understand much about electric motors. I met a tech entrepreneur from California who said his firm is working on a motor that absorbs the EMF given out by a motor and feeds the energy back into the battery. I listened politely having no clue if this is possible or not and whether it is worthwhile even. Welcome any opinions from the experts.

Eventually improvements in motors and batteries will be needed to make EVs truly attractive.
Thank you Sir.
In a vehicle a there is a lot of scope for power generation from passive components, like the vehicle suspension which is a source of linear motion. The complexity of converting the linear motion into power is in the hands of people in the know, there are some papers on it.

Watch makers are doing it converting linear motion into electricity, Seiko Kinetic.

Quote:
Originally Posted by alpha1 View Post
What would be the life of the permanent magnets?
And what precautions does one need to take to ensure their longevity?
I'm also looking for an answer to this, time and temperature makes them weaker.

Quote:
Originally Posted by LiCoO2 View Post
PMSM and brushless dc motor are almost the same thing. They have small constructional differences but the physics is same.
Does it have to with one being AC (PMSM found in cars) and the other being DC (BLDC) and the related controllers?

[quote=LiCoO2;4621047]
There is also a new technology called axial flux motors which have extremely high power density that are being developed for electric planes. However, I personally donít see them coming to mainstream cars for a long time.

A good discussion thread on this topic:
https://electronics.stackexchange.co...ad-of-a-dc-one[quote]

Thanks. I didn't know about Axial Flux motors.

Quote:
Originally Posted by LiCoO2 View Post
Coming to the original question that you asked, the power of the motor doesnít matter much when it comes to range. You see, motors are extremely good at taking what they need i.e. the amount of energy that a motor will demand from battery only depends on the load that its experiencing. And the only thing that determines load on the motor are the weight of the vehicle, vehicle speed and acceleration. You can put a million kW motor and it will still give you the same range if these 3 parameters are kept the same. So if you want to a better range, reduce the driving speed, acceleration and weight.
Got it, so basically the motor will draw only as much as required and 100kW or 150kW shouldn't matter.
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Old 15th July 2019, 15:05   #9
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by Sankar View Post
Does it have to with one being AC (PMSM found in cars) and the other being DC (BLDC) and the related controllers
No.

The only type of motor that can run on DC is a brushed DC motor. They have brushes in them. They are the kind of motors that you will find in old toys.

induction motors, PMSM, bldc, switched reluctance are all brushless and hence need alternating current to run.

PMSM and BLDC are the same thing for all practical purposes. In practice, small PMSM motors are called BLDC in day to day usage while the big motors (>30 kW) are called PMSM.

But if you really want to get technical, hereís a good academic discussion: What is the difference between BLDC and PMSM motors?

A better term for PMSM and BLDC would be synchronous motor.

Induction motors are asynchronous motors.

Hereís a good video on different types of motors:
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Old 15th July 2019, 17:30   #10
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by LiCoO2 View Post
A better term for PMSM and BLDC would be synchronous motor.
I don't remember my electrical machines fundamentals after 30 years... However, isn't synchronous motor essentially an AC motor, since it must run at the frequency of the AC voltage?

What is this synchronous DC motor?
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Old 15th July 2019, 18:25   #11
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Default Re: Electric vehicles - Types of motors?

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Originally Posted by Samurai View Post
I don't remember my electrical machines fundamentals after 30 years... However, isn't synchronous motor essentially an AC motor, since it must run at the frequency of the AC voltage?

What is this synchronous DC motor?
BLDC is essentially a motor with built in SMPS , so it's fed by DC but internally there is AC at the frequency of motor, that is switching happens sensing position of rotor thus synchronous.

In fact in classic carbon brush DC motors also the current was alternating in the coil because as the rotor moved the direction of current was switched.

AC or DC is w.r.t to the input and not what runs in coil ( always AC)
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Old 16th July 2019, 00:44   #12
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by Sankar View Post
Proper and almost practical as a daily driver electric vehicles are now at our doorstep (Kona, Ather etc) and just like we used to discuss various internal combustion engine types i think it is time for us to start discussing electric motors.

What are the advantages and disadvantages of each type of electric motors
for use in a vehicle? For starters, which among the three types listed below is the better motor? Only Tesla seems to use an AC induction motor while the rest are going with permanent magnet types. Also doesn't the strength of a magnet reduce over time and in high heat conditions?
Sankar, unfortunately, a lot of information online, esp the Simpler versions (eg Wikipedia is incorrect) and was written by people who do not practice electrical engineering or study it.

I would recommend trying to find this textbook
ISBN 9780470604465 (Introduction to Robotics). This goes into a lot of details into all types of motors.

From a motor standpoint, the lines between DC and AC motors a blurred. Eg DC brushless motors are called hybrid motors. They cannot run on DC current. you have to supply DC current to a controller and that actually supplies the waveform.

As far as Testla is concerned they use Pulse Width Modulation control Variable Frequency drive.
you can read more about VFDs here
https://www.ecmweb.com/power-quality...equency-drives

Electric car motors are mostly VFDs of various different types.

Are they DC or are they AC, it does not really matter all that matters is you understand how they work and the above link does a good job.
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Old 16th July 2019, 09:18   #13
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by tsk1979 View Post
Sankar, unfortunately, a lot of information online, esp the Simpler versions (eg Wikipedia is incorrect) and was written by people who do not practice electrical engineering or study it.

I would recommend trying to find this textbook
ISBN 9780470604465 (Introduction to Robotics). This goes into a lot of details into all types of motors.

From a motor standpoint, the lines between DC and AC motors a blurred. Eg DC brushless motors are called hybrid motors. They cannot run on DC current. you have to supply DC current to a controller and that actually supplies the waveform.

As far as Testla is concerned they use Pulse Width Modulation control Variable Frequency drive.
you can read more about VFDs here
https://www.ecmweb.com/power-quality...equency-drives

Electric car motors are mostly VFDs of various different types.

Are they DC or are they AC, it does not really matter all that matters is you understand how they work and the above link does a good job.
I didn't wait after reading your post, searched on Amazon found that book (by Saeed B.Niku) and made an order. Thanks Tanveer.
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Old 16th July 2019, 09:45   #14
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by Sankar View Post
Yesterday i was thinking why Hyundai couldn't give us a model with 64kWh battery and the lower powered 100kW motor of 39kWh model for an even better range than a 64kWh battery with 150kW motor could provide. Or is it possible to de-tune the 150kW PMSM motor in 64kWh Kona to 100kW or lower output which makes that large battery and low power motor variant totally redundant.

For a 1 Ton car to balance 100 kph on a flat road the power requirement will be something like 12kw. The motors generate only what is necessary to overcome the load applied on them. That is exactly why you see the current vary when load varies.
Everything beyond the balancing load is the acceleration reserve, and will be only used during acceleration.
If you ever see an engineer downloading data from the Volvo Hybrid bus, at just below 20kph in city traffic the motor is actually working below 10kw when it comes to 20 it shifts from electric to diesel. Even though it is powered by a 120kw motor. The very quick 0 to 40 kph is what the 120kw motor provided. Note that this is a 16 ton bus I'm talking about.
https://www.volvobuses.in/en-in/our-...vo-hybrid.html



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Old 16th July 2019, 12:15   #15
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by Sankar View Post
I didn't wait after reading your post, searched on Amazon found that book (by Saeed B.Niku) and made an order. Thanks Tanveer.
Great!
While for software there are excellent resources available online, I have seen for pure engineering related stuff, especially Electrical, VLSI and Mechanical engineering you often have to dig into a textbook.

some very good textbooks
These are used in Engineering courses in India and therefore are very cheap with Indian editions.
  • Clayton A E & Hancock N N, Performance and Design of DC Machines, ELBS, 1971
  • Langsdorf A S, Theory ofDC Machinery, McGraw Hill, 1999
  • Nagrath I J & Kothari D P, Electric Machines, 3rded, Tata McGraw Hill, 2004
  • Say M G, The Performance and Design of AC Machines, CBS, 1983
  • Chapman S J, Electric Machinery Fundamentals, McGraw Hill, 1999
  • Toro V D, Electrical Machines and Power Systems, Prentice Hall, 1988
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