Re: An interesting BLDC controller concept

Chris Carlen wrote:
David Brown wrote:
There are (I believe) two main forms of windings for this sort of three phase brushless DC motors - BLDC windings, optimized to be run by trapezoidal waveforms, and PMSM windings, optimized for sinusoidal waveforms. Of course, you can use either waveform for either type of motor winding, at a slight efficiency loss, but there is no point in striving to get a nice sinewave unless you are sure your motor matches it, and unless you can be sure of very smooth running.

Are you referring to slotted vs. slotless stators? If so, which of your designations "BLDC" and "PMSM" is slotted/slotless? Also, what does the abbreviation PMSM mean?


I haven't heard the terms "slotted" and "slottless", so I'm afraid I can't help you.

"PMSM" is "permanent magnet synchronous motor".

I had a discussion with a sales engineer at http://www.aerotech.com about slotless/slotted motors. It wasn't clear from this discussion though which should be driven with trapezoid vs. sine.

There also doesn't seem to be clear guidance from motor manufacturers about this.


That's certainly true, at least for all the motors I've seen.

One thing is certain, my Maxon motors produce perfect sinewave back EMF waveforms. I wonder if a slotted motor would produce something more "trapezoidal?"


Actually Maxon motors can be driven well with either form, and it is not clear from their documentation (that I've read) which is optimal. I think they work well enough with either kind of driving.

As for using a PLL based on the hall effect sensors - you do realise that the 6 switching points from a typical motor hall effect sensor setup are not accurately at 60 degree steps? You are going to get some serious jitter effects if you try and multiply the step rate, unless you just use a single step (i.e., one signal per electrical revolution).

Yes, they are not perfectly accurate. I think I was inclining just toward looking at a single pulse/rev. Though now it brings up an interesting refinement:

A controller could calibrate itself to the hall misalignment by running the motor in a PLL and measuring the hall timings. Now I have to think about how this information could be used later to correct the hall timings...but there must be a way. Probably would have to be a digital PLL implementation of some sort.



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