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We have a 3-phase BLDC motor with 3 Hall effect sensors. I believe the motor is star connected but the datasheet has little information and we are still trying to obtain this information from the manufacturer.

Researching online, I have understood that 3-phase BLDC motors can be controlled trapezoidally (60° or block control), sinusoidally or with field oriented control.

My understanding was you could use any of these control methods on any BLDC motor; which one you choose depends on your application (with sinusoidal control allowing for constant speed and torque output whereas field oriented control outputs the greatest torque as the stator magnetic field is perpendicular to the rotor permanent magnet's field).

Is this correct so far?

If yes, why might a motor manufacturer say "our motor is wound sinusoidally" as if to suggest the physical windings have been wound in such a way ONLY sinusoidal control can be used? Or might they have said this because they prefer you to use sinusoidal control but in reality, you could use any?

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  • \$\begingroup\$ FOC will probably work slightly better with a sinusoidal wound motor. All the theory and math assumes the back EMF is sinusoidal. In a motor specifically intended for trapezoidal control, little effort might be put into making it sinusoidal. But you can control any motor with any of the various algorithms. Any differences will be relatively subtle (such as torque ripple or vibration, etc). \$\endgroup\$
    – user57037
    Sep 17, 2022 at 3:02
  • \$\begingroup\$ For some applications, e.g., high-end positioning applications, it is probably much better to make a servomotor using sinusoidal back EMF (although they do have encoders so maybe it isn't THAT critical). \$\endgroup\$
    – user57037
    Sep 17, 2022 at 3:04

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Technically you could, but matching your drive method to the shape of the BEMF waveform produced by the motor is more efficient.

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  • \$\begingroup\$ So would I be correct in saying BLDC motors can be physically wound 'Sinusoidally', 'Trapezoidally' or where the windings are equally distributed around the stator? If this is correct, what other windings configurations are possible? \$\endgroup\$
    – MRB
    Sep 16, 2022 at 16:08
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    \$\begingroup\$ @MRB I've only ever heard of windings wound to produce a trapezoidal or sinusoidal BEMF pattern. Theoretically, you could probably produce many other shapes if you wanted but little practical purpose. Sinusoidal matches AC sources and trapezoidal matches easy to make switching sources. I'm not even sure what they do to the windings or stator to determine the BEMF shape to begin with. \$\endgroup\$
    – DKNguyen
    Sep 16, 2022 at 17:23
  • \$\begingroup\$ Also, so-called trapezoidal back EMF motors still produce a somewhat rounded back EMF. \$\endgroup\$
    – user57037
    Sep 17, 2022 at 3:04

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