Re: [avr-chat] BLDC control with ATmega128?

[Rolf Magnus]

On Friday 03 February 2006 09:35, David Brown wrote:

> > Has anyone attempted this? I was hung up on the fact that there are 6
> > 16-bit PWM generators, but then realized I only needed 3 (plus 3
> > GPIOs), and I think it can be done with a single PWM, 6 GPIOs and
> > some external logic.
> >
> > In any case, has anyone done this, and can you offer any advice? Thanks!
> >
> > --
> > Rick
>
> It should be perfectly possible (assuming you have hall-effect sensors on
> the motor). 

It also works with sensorless motors, using back-EMF sensing. An ATmega128 is 
vastly oversized for this task. An ATtiny2313 or an ATmega8 are enough.
See the following links (of which most are in german though):

http://home.versanet.de/~b-konze/blmc_flea/blmc.htm
http://www.bldc.de/forum/viewforum.php?f=2&sid=9dd24b969162caf15865d948376cc1af
http://www.speedy-bl.com/electr.htm
http://www.rcgroups.com/forums/showthread.php?t=140454

They are all about sensorless bldc motor controllers for RC models.

There are also some application notes that can help, like Atmels AVR443 and 
444, where an ATmega48 is used. See:

http://www.atmel.com/dyn/general/advanced_search_results.asp?device=1&tools=1&faqs=1&datasheets=1&appNotes=1&userGuides=1&software=1&press=1&articles=1&flyers=1&checkAllReference=1&target=brushless

irf.com also has some appnotes.

> I don't think there is any real advantage in using PWM for both the top side
> and bottom side transistors for a BLDC motor

irf's appnote an-1048 talks about this. Doing the PWM on all transistors can 
have the advantage of an even distribution of switching losses (if you use N 
channel fets on both high and low side and do proper gate driving). Another 
alternative that also gives you an even distribution is to do the PWM on the 
high side during half of a commutation cycle and on the low side during the 
other half.

> (as distinct from a PMSM, where you *do* need them).