BLDC: Asymetrical Zero Cross detection

Hello,

for detecting the Zero-cross of a sensorless BLDC I use a starpoint reproduction and give this Neutral-Point-signal and the evaluated Phase to a comparator. At higher speed there is no problem with zero- cross detection. But at lower speed, the zero crossing detection is asymmetrical: The falling edge comes late, the rising edge comes very soon. So the following phases of the runngin motor are long - short - long - short ....

Who knows something about this effect?

Best regards

Wolf

Reply to
Wolfgang
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I'd like to try and help, but even though I'm more or less conversant with motor theory and electronics, the terminology here is unfamiliar to me. What's BLDC? Is this a generator or a drive application, is there speed control electronics involved. A bit more info on the situation would assist.

Is your phase set stiff and reasonably sinusoidal?

Reply to
Bruce Varley

Brushless DC? A schematic would be good.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

snipped-for-privacy@r36g2000vbn.googlegroups.com...

Brushless DC. Undoubtedly drive -- if it were a generator one would just be rectifying, which is a fairly easy problem. It sounds like the OP is designing the drive electronics -- for sensorless BLDC (i.e. brushless without commutation sensing) you use back EMF to figure out the motor phase.

Reply to
Tim Wescott

A DC bias would cause that effect.

Jerry

Reply to
Jerry Avins

On 26 Okt., 15:01, Tim Wescott wrote: =A0It sounds like the OP is

Yes - you are right.

Wolf

Reply to
Wolfgang

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