PMSM And SRM- Electric Motors For EV, Advantage ...

28 Oct.,2024

 

PMSM And SRM- Electric Motors For EV, Advantage ...

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Introduction to Switched Reluctant Motors (SRM)

The switched reluctance motor (SRM) is a reluctance torque-driven DC electric motor. Unlike most brushed DC motors, power is routed to the stator (case) windings rather than the rotor.

It emulates the behavior of an AC motor by switching the DC between the stator windings.

It complicates electrical design because power must be delivered to the various windings via a switching mechanism. Electronic devices can accurately time current switching, making SRM designs easier.

The switched reluctance motor operates on the changing reluctance principle, which implies that the rotor of this motor is constantly aiming to align through the lowest reluctance lane.

The rotational magnetic field can be produced with the help of a power electronics switching circuit.

Advantages of Switched Reluctant Motors (SRM)

Construction is straightforward and robust.  No windings, slip rings, brushes, etc are included in the rotor as a result it is easier to maintain than other types of motors.  There&#;s no static magnet. 

Ventilation is easier as losses take place mostly within the stator.  Power semiconductor switching circuitry is easier. 

It&#;s possible to urge very high speed.

Disadvantages of Switched Reluctant Motors (SRM)

Torque-rippling causes noise pollution at medium to high speeds  Stator phase winding should be capable of carrying magnetizing current.  It requires position sensors.

Introduction to Permanent magnet synchronous motors (PMSM)

Permanent magnet synchronous motors are a form of AC synchronous motor in which the field is stimulated by permanent magnets, which produce sinusoidal back EMF. 

It has the same rotor and stator as an induction motor, but the rotor is a permanent magnet that creates a magnetic field. As a result, the rotor&#;s field winding does not need to be wound. It is also known as a 3-phase Brushless permanent sine-wave motor.

It is regulated by the synchronously rotating magnetic field that generates electromotive force. A rotating magnetic field is formed in between the air gaps when the stator winding is activated by a 3-phase supply.

When the rotor field poles maintain the revolving magnetic field at synchronous speed and the rotor rotates continuously, the torque is produced. Given this fact, these motors are not self-starting, a variable frequency power supply is required.

Advantages of Permanent magnet synchronous motors (PMSM)

Torque ripples are absent.  High-Performance efficiency (output to input ratio)  Availability in different sizes.  Smooth torque.

Disadvantages of Permanent magnet synchronous motors (PMSM)

We need a control system as we can only change the stator current.  There are no self-starting motors.  There is a high initial cost involved.  Performance on PMSM depends on the quality of the magnet used.

Why PMSM or SRM are used rather than traditional and cost-effective Induction Motors to manufacture EVs?  Let&#;s talk about Induction Motors in brief-

SRM Vs PMSM Motors in Electric Vehicle?

The invention was brought up by Nikola Tesla in . The basic principle of the working of induction motors is electromagnetic induction where the magnetic field generated around the conductor induces current due to continuous rotation. This induction motor functions with the flow of AC induction.

The above-discussed principle of electromagnetic induction creates a minute delay which is known as slip. Due to the induced current flow, there is a noticeable difference between the motor speed due to the magnetic field and the rotating shaft speed.

Therefore, to remember in an easier sense, these induction motors are termed as &#;Asynchronous Motors&#;.  Now, that we have an idea about Induction Motors, let us understand why PMSM is better than induction motors.

  • Firstly, PMSM is a synchronous motor whereas the induction motor is an asynchronous motor. Slips produce torque in induction motors, sometimes slips are unnecessary and lead to energy losses and decreasing efficiency of the induction motors.

  • Secondly, PMSM is designed in such a way that it has a higher performance output compared to Induction Motors. (You can refer to the graph given below when both motors are compared based on power factor).

Power Factors of IM and PMSM under different load rangesThe above graph indicates PMSM&#;s consistent efficiency under different load ranges.

This eventually indicates energy saving during its EV&#;s running span.

  • Thirdly, Permanent magnet synchronous motors PMSM can generate torque even at zero speed ensuring smooth pickup and braking operations compared to induction motors.

    Goto Windmax Power to know more.

Lastly, EVs are being manufactured in large masses where the more efficient and sustainable motor will lead the motors&#; demand in the EV market.  One of the most controversial and complicated motors amongst different motors. SRM has been understood for a long time yet this wasn&#;t much in use for electronic advancements.

So why do we use PMSM Motor?

When we compare SRM and IM, they are just better and worse in some situations.

SRM has more power density but lacks in keeping up the power factor against IM. There are more vibrations caused by SRM due to torque ripples while it can generate a huge amount of torque in the shortest time when compared with other electric motors. 

There needs to be a better arrangement for operating SRMs (starting and syncing).

There have been optimizations taking place but those are just minor improvements in SRM advancements.  The recent noticeable advancements have been observed in the Tesla Model 3 and Toyota Prius.

I am talking about the IPM-SynRM electric motor, The Toyota Prius is an HEV with a single magnet piece but it wasn&#;t as revolutionary as the Tesla Model 3.  The EV Markets are rising like never before and everyone is just so excited to notice and learn about the different advancements going on recently.

Top 5 Electric Motor Manufacturers in India

The Rebel EV industry has a large number of electric motor manufacturers: here is the list of the top 5 electric car motor manufacturers in India.

Tata AutoCorp, General Motors, Virya Mobility, Nidec Corp., Aisin Seiki Co. Ltd., etc.

Advantages of Reluctance Motor

Simple motor construction. Low rotor inertia facilitates high starting torque. These motors produce high self-inductance. Can produce variable speeds at constant power outputs.

Switched Reluctance motor vs BLDC for EV

BLDC motors perform better when compared to SRMs at high speeds.

SRM is more cost-effective than BLDC motors. When both these motors are under high-power applications, SRM motors perform much better than BLDC motors as SRM are cooler during their operations.

SRM vs IM

As discussed in this article, SRM has a higher power density than IM. Due to high power density, SRM performs operations more efficiently than IM. IM is more cost-effective than SRM.

Permanent Magnet (PMAC) Motors & Electrically ...

You understand the differences between premium efficiency (IE3) motors and PMAC or ECM motors (IE4&5). You understand the cost implications of both styles of motors. Is there anything you need to know about selection and commissioning of these motors? The R. L. Deppmann Monday Morning Minutes may offer a few tips.

What is Special About Selecting Permanent Magnet Motors?

We engineers love lists. Here is a list of selection thoughts on PMAC motors for pumps.

  1. PMAC motors are only available to about 30 HP. Verify the motor is available in the HP you need and the approximate increase in cost before you specify them.
  2. PMAC motors tend to be a smaller frame size than standard premium efficiency motors. Make sure the pump frame and the motor frame match. These motors do not always follow the standard NEMA T-frame motor frame charts currently published.
  3. When replacing an existing motor, verify if the pump needs any modification since the frame size maybe smaller.
  4. These motors MUST have a variable frequency drive to work (VFD). They will not work with across the line or part load starters.
  5. You cannot use a drive with a manual or automatic bypass because the motor needs a VFD.
  6. When selecting the pump, use the true synchronous RPM curve. Example: RPM, not RPM.

Commissioning the VFD on a Permanent Magnet Motor Application

The startup of the variable speed drive (VFD) on a PMAC application requires some special knowledge about the drive and the motor. If the pump supplier is supplying the drive and the startup services, there may be less RFIs requesting information not shown in the submittals. Here are a few things of importance.

  1. The VFD should be supplied for use with a permanent magnet motor. Many PMAC motor manufacturers list drives they have tested with their motors. This might be a time to have the drive provided by the pump supplier for unit responsibility.
  2. I mentioned the hertz in the last article, and some people thought it was a typo. It was not. The design speed of the motor is NOT running at 60 Hz. The motor has a large speed range and the person setting up the VFD has to &#;tune&#; the motor to the correct speed. One motor may be 150 Hz to get RPM while another might be 90 Hz. This is motor specific and may or may not be on the motor tag.
  3. Some added points are the rotor resistance, the two inductive values of Ld and Lq, and the emf back voltage. The point is, there is a lot of information needed to set up the drive. It is not something a novice should tackle. The specifier should require a startup report for the owner with the PMAC specific values in the report.

Look at the two motor tags above. The same manufacturer has one tag with all the information needed and one tag without. The R. L. Deppmann Startup and Warranty Department technician would have the correct information available before getting to the project.

Advantages and Disadvantages of Permanent Magnet Motors?

Here is a brief and possibly incomplete listing of the advantages and disadvantages of using a PMAC motor over a premium efficiency motor.

ADVANTAGES

  1. The PMAC motor has a higher efficiency than the motors you currently specify. This efficiency is even more pronounced at lower speeds and lower horsepower.
  2. The higher efficiency produces lower electric bills for your client. Payback may be as low as 3 years.
  3. The PMAC motor is noticeably quiet. The motor is quiet at full speed and has much less &#;whine&#; at lower speeds.
  4. ECM motors are only available in lower horsepower, but they normally have a variable speed adjustment inside of them and they do not need a drive. Visit part 1 of this series for more detail.
  5. ECM &#;Smart pumps&#; also include some control functions for the pump. Again, visit part 1 of this series for more information.
  6. If you are an early adopter engineer, this is the latest and most efficient choice for you.

DISADVANTAGES

  1. These motors come with a first cost premium. They are not required by code so the owner and engineer should be on the same page before the value engineering options come forward.
  2. The project may have some pumps with PMAC motors and some where the PMAC is not available. The plans and specifications should be clear on this.
  3. VFDs must be supplied for these motors to work. The drive must be specified for use with PMAC motors.
  4. The startup of the VFD and pump will need more professional knowledge and motor information. Deppmann does their own startups with trained professionals.

A Word about R.L. Deppmann and Monday Morning Minutes as Ends

R. L. Deppmann is very committed to being the company we say we are. Our core values are:

 

Knowledge

Responsiveness

Empowerment

 

Our core purpose beside making money is:

 

We exist to help people make better decisions.

 

The R. L. Deppmann Monday Morning Minutes (MMM) series exists to help you make better decisions. The MMM will provide you with the knowledge we have of our industry&#;s systems and products. As you read MMM and think about the articles, we expect that you can respond better to your customers. Our staff is empowered to respond to your questions and challenges to the content. If you have comments about the MMM series or have a subject you want us to cover in the future, please contact us by clicking here.

Happy New Year to Everyone from the R.L. Deppmann Employee Owners