How Tesla model - 3’s electric motor works and it’s details

January 22, 2021

ABOUT THE AUTHOR

Yogeshwari S Gaddam, B.E in Electrical Engineering Currently she is working at Imajey consulting engineers pvt. ltd. as a Team lead for Visual Education. She is passionate about understanding the physics behind complex technologies, such as motors: Induction motors, SynRM motors, and IPM-SynRM motors and explaining them in simple words. To know more about the author check this link

Introduction to Tesla Model 3's IPM-SynRM

In this article I will take you on a journey through the working of Tesla model -3’s electric motor, IPMsynRM (Internal Permanent Magnet Synchronous Reluctance Motor). I will explain the evaluation of this motor in detail. Without any further due lets learn.



Tesla-S’s motor

Before starting this, i want to explain to you in short about Tesla-S’s motor. Everyone knows that induction motors are used everywhere in this electrical world as shown in the Fig:1A at left side. For long drives at cruise speed, losing 3% to 4% of energy to generate currents in the rotor bars is not up to the mark. That's why to overcome this issue Tesla engineers have replaced it with a PM motor(Fig:1A) at right side. If they use it, they do not experience energy loss in the rotor. There is no need to generate current, also it produces good torque at high speed. But here we also have another issue, back EMF and eddy currents losses. Let’s try to resolve this problem.

Fig:1A Illustration of Tesla-S’s motor : Induction Motor and PM Motor
Fig:1B Back EMF

IPM-SynRM motors(SynRM + PM motor)

The solution is here, an integration of a SynRM motor and a permanent magnet motor is used(Fig:2A). The PM motor is good for high speed, whereas SynRM is efficient and it has no back EMF issue.

You can see Fig:2B below, this motor has a simple design. The Magnet has been placed into the slotted cuts of the SynRM motor, deep within the iron core. This placement will help to reduce back EMF issues on the stator windings to major extend. This design is the Tesla Model 3’s Electric motor. Now let's discuss in detail Working of Tesla model -3’s IPM SynRM electric motor in the next section.

Fig:2A IPM-SynRM is an Integration of SynRM motor and PM Magnet motor
Fig:2B Magnets are placed deep within the iron core

FEA illustration:

Now we need to analyze this motor more. Therefore for your better understanding I have added an FEA simulation to observe the Resultant magnetic field produced by this Permanents magnets arrangement. The FEA software EMWorks 2D, paired along Solidworks, comes to the rescue. If these magnets were placed far apart, each magnet would create its own magnetic field as shown in the fig below, using this resultant field let’s do further analysis.

Fig:3 FEA simulation of RMF produce by PM arrangement

Torque analysis

In the latest IPM-SynRM design, remove the iron core and keep only the permanent magnets as shown in the Fig:4 at left side. At this RMF position, the permanent magnets will not experience torque, as there is no tangential component for these four forces, and the torque the remaining forces produce cancel each other out(Fig:4 Right side).

Fig:4 In Latest IPM-SynRM design, remove the iron core and keep only the permanent magnets

If the RMF is rotated by 45 degrees, we get maximum torque out of permanent magnets. If rotated again by 45 degrees the torque the rotor produces goes to zero again.

Fig:5A IPM-SynRM-Design
Fig:5B Again RMF is rotated by 45 degrees, torque become zero again

Now the iron part of the rotor has an opposite effect on the same technique. Let me summarise it for you. At the initial angle, torque production will be zero because it’s a perfectly misaligned and symmetrical case(Fig:6A). When we slightly offset the RMF, the rotor will experience a negative and maximum torque. When RMF reaches 45 degrees(Fig:6B), the torque becomes zero again, because this is a perfectly symmetrical case again. As we further rotate the RMF, the reluctance torque produced will be positive.

Fig:6A At Initial angle Torque is become zero
Fig:6B At 45 degree angle Torque is again zero

Combined torque - at 50 degrees

Now let's analyze Tesla model-3’s motor, If the RMF angle is around 50 degrees, we’ll get maximum torque from the motor. So Tesla Motors engineers made sure that when you start the car, the RMF angle is around 50 degrees, which will guarantee maximum torque production(Fig:7A).

Please keep this in mind as the motor speed increases, and the PM induces a back EMF on the stator coil. Here the solution at high speeds is to align the RMF opposite to the permanent magnetic field.

As you can see, the RMF weakens or almost cancels the permanent magnet field(Fig:7B). This way, even at high speeds, such motors won’t produce much back EMF. Obviously, at this stage the torque production will mostly come from the reluctance effect.

Fig:7A RMF angle is around 50 Degree
Fig:7B RMF weakens

Model- 3 uses a six-pole design, which is no different than a four-pole design, apart from getting higher torque.

Fig:8A 4-Pole and 6-poles design of Tesla model-3's motor
Fig:8B Graph

IPMSynRM used in the Toyota Prius, a hybrid electric car

Do you know this innovative motor is also used in another car? In the Toyota Prius, a similar IPMSynRM motor technology is used. What is the difference between both? Prius uses solid magnets, whereas each magnet in Model 3 is segmented into four parts as shown in the Fig:9. This segmentation reduces the eddy currents in the magnets, preventing them from overheating, which in turn saves them from demagnetization and runs the motor cooler.

Fig:9 Prius motor is also using IPM-SynRM motor

The 2019 version of model S cars have IPM-SynRM fitted at the front wheel. You can see the comparison here why tesla 3’s motors are now at top in the EV world than the induction motors.

1. Ipm-SynRm motors are 96% Efficient, as compared to induction motors are 94% Efficient.

2. Effective cooling is easy to do in IPM-SynRM, but in an induction motor it is tedious.

With the help of these improvements, IPMSynRMs have definitely set new standards in the EV world.

We hope you understood and enjoyed this explanation of how Tesla model -3’s electric motor works and its details.

I have also explained the Tesla model 3’s electric motor in simpler fashion which you can check this link Tesla model 3’s electric motor.

Other more Articles:

How synchronous reluctance motor work?

Basics of synchronous reluctance motor

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