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Bench Talk for Design Engineers

Bench Talk

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Bench Talk for Design Engineers | The Official Blog of Mouser Electronics


Of Machines and Motors Caroline Storm Westenhover

 

Last semester I took a machine and motors class. It has got to be one of the more difficult classes I have ever taken. Not only because it dealt with magnetism (the bane of many an Electrical Engineer) but also because it dealt with transformations. You know a subject is challenging when the easiest solution is to transform to a different reference frame, solve the problem in the new reference frame, then transform it back to the original. Luckily some Ivory Towered Genius developed a transformation matrix. But the transformation matrix changes based the type of motor and the shape of the rotor, and boy are there some really non-uniform rotors. My last project involved 7th order harmonics, each requiring its own multiple reference frames to solve. Why, oh why, drag me through these complications? Well, turns out there is an answer for that.

It is one of the fundamental complications of motor design and of the power grid that motors require controlled oscillating electromagnetic fields to operate; making them reactive loads that need rectified AC to operate. They have all the equipment of a DC load, requiring power electronics to rectify the AC source, and all the complications of an AC load, reactive power, and s-domain models. Motors also represent a difficult intersection between electrical and mechanical. All of the modeling I did was electrical, with no thought to modeling what could happen to the material. It takes a good team of electrical and mechanical engineers to develop a good motor. Yet motors are the optimal drivers for many appliances, so we assemble teams, model all aspects, and finally come up with working designs.

Perhaps this is just a student stumbling on old truths. But looking at commercially available motors, I am rather impressed with all the options the different motor types and oddly shaped rotors provide. Is a small size worth a higher price tag? Then a Permanent Magnet Synchronous Machine is the one for you. Is maintenance going to be consuming and expensive? Brushless DC it is. Companies are even beginning to resurrect designs that happen to fix new problems.  But what about those crazy shaped rotors that create all sort of weird back EMF requiring a separate reference frame for every major harmonic? Yeah, turns out that is mostly academic.

 

 

Kals, Sammine. 3 Phase Generator Winding Diagram. Digital image. From Wind. Blogspot, 3 Mar. 2015. Web. 27 Dec. 2015.



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My name is Caroline Storm Westenhover. I am a Senior Electrical Engineering student at the University of Texas at Arlington. I am the third of seven children. I enjoy collecting ideas and theories and most enjoy when they come together to present a bigger picture as a whole. Perhaps that is why I like physics and engineering.  My biggest dream is to become an astronaut.


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