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Back:EMF and energy conversion in a PMSM

  1. Jan 31, 2016 #1


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    I'm seeking comments & opinions on a couple of statements I've come across in a book: "A text book of electrical technology" https://books.google.co.uk/books?id...ved=0ahUKEwiI9MH7ntTKAhXDRhQKHalHBEAQ6AEIHzAD (amongst others) that states:

    "In fact, it seems to be one of the fundamental laws of Nature that no energy conversion from one form to another is possible until there is some one to oppose the conversion. But for the presence of this opposition, there would simply be no energy conversion.... whereas in motors back-EMF does this job."

    Or more succinctly put in other places as: "Back-EMF is fundamental to the conversion of electrical energy to mechanical energy in a BLDC motor".

    Thoughts? Supportive or against?

    (Simple) scientific explanations to support or refute the statement?
  2. jcsd
  3. Jan 31, 2016 #2


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    Gold Member

    I think it should be: for the absence of this opposition . . . .

    Back-EMF in the motor is due to induced voltage in the coils, meaning that there is some (varying) magnetic flux through the coils.
    The magnetic field in the airgap contains magnetic energy density. When the motor turns, it will try to minimize the volume of the magnetic field ( limiting the volume to a space between opposite north- and south- poles ), thus minimizing the amount of magnetic enegy. The loss of magnetic energy is converted to mechanical energy.
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