Article on Brushless Motor Terminology 2

Hi All:

I have an article up at engineering.com that covers common points of confusion on brushless motor terminology. It can be found here:

http://www.engineering.com/Designer...icleID/8131/What-is-a-DC-Brushless-Motor.aspx

A DC brushless motor is an AC motor. Specifically, it is a permanent-magnet synchronous (AC) motor (PMSM).

So why, you may ask, is it called a DC brushless motor?

The term "DC brushless motor" is a marketing term. The intent was to sell these motors as replacements for DC brush motors in servo applications....

For a long time this had been kicking around in my head as an FAQ for this motors forum. Would you like to see a form of it here? If so, what additions and/or changes would you like to see?

Curt Wilson
Delta Tau Data Systems

 

[electricpete]

Oh, so that's why they call is a brushless dc motor.
I always wondered about that. Good article.

=====================================
(2B)+(2B)' ?

 

[DHambley]

That article explained a lot, Curt. Thanks.

Darrell Hambley P.E.
SENTEK Engineering, LLC

 

[Brad1979]

Nice article. Have you read James Mevey's thesis "Sensorless Field Oriented Control of Brushless Permanent Magnet Synchronous Motors?" In it he has a nice section discussing terminology. He did a literature search and found the brushless PM motors have been called the following names:

[ul]
[li]BACM brushless AC motor[/li]
[li]BDCM brush/brushless DC motor[/li]
[li]BLDC brushless DC[/li]
[li]BLSM brushless servo/synchronous motor[/li]
[li]BPM brush/brushless PM[/li]
[li]ECBM electronically commutated brushless motor[/li]
[li]ECDCM electronically commutated DC motor[/li]
[li]EDCM equivalent DC motor[/li]
[li]PMAC permanent magnet AC[/li]
[li]PMBDC permanent magnet brush/brushless DC[/li]
[li]PMDC permanent magnet DC[/li]
[li]PMSM permanent magnet synchronous motor[/li]
[li]SPM sinusoidal/surface/synchronous PM[/li]
[li]SPMSM surface PM synchronous motor[/li]
[li]SMPMSM surface mounted PM synchronous motor[/li]
[/ul]
My preferred terminology is what you use in your article - PMSM. I'm not even a fan of "trapezoidally wound" and "sinusoidally wound" because it's more of a continuum than separate buckets that they are placed in. When I get asked about this I usually just say that all PMSM's are functionally the same in that their method of torque production is identical. The main difference is that different PMSM's can be designed with different rotor-stator flux linkages to meet different design goals.

 

[cswilson]

Brad: Thanks for the info. I had not seen that thesis, but I have seen most of the terms. PMSM is what I see most often in the serious technical literature -- IEEE papers and the like.

However, I disagree on "trapezoidally wound" versus "sinusoidally wound". I see it more as a dichotomy instead of a continuum. I don't see any point in making a motor somewhere in between the two. That said, the waveforms for trapezoidally wound motors are further from true trapezoids than sinusoidally wound motors are from true sinusoids, and different trap motor designs have different variations from the ideal waveforms.

But the biggest issues I see in the field come from using one type of motor when the other should be used (or using an inappropriate commutation algorithm for the motor design).

 

[Clyde38]

Interesting article. . . As I remember, early “Brushless DC” motors were an attempt to remove the mechanical commutation (brushes, commutator bar, brush rigging, etc.) and replace with electronic commutation (no brushes, “Brushless DC”). With the exception of the influence of the mechanical brush rigging vs. electronic commutation, the performance (Torque vs. Speed) was equivalent to the “DC Brush” motor. Three phase induction motors were well suited to do this by using the existing three phase induction stator and replacing the squirrel cage rotor with a permanent magnet rotor an commutate the stator winding by having shaft position feedback to sequence the phases. The type of electronics (drive scheme) has somewhat influenced naming varieties for this motor (for example six step vs. sine etc.)