On Fri, 13 Apr 2012, Stephen Dubovsky wrote: > Date: Fri, 13 Apr 2012 18:14:41 -0400 > From: Stephen Dubovsky <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] 3 phase bldc question > >> Cogging in BLDC/PMSMs is because of square wave drive currents >> > > Not exactly. There are 2 things at play here. > > 1) Cogging is from the variable reluctance based on rotor angle. It has > nothing to do w/ the drive waveform. It exists even when the leads are > open circuited. In simple terms, the magnet is getting closer/farther from > a pole that forms a magnetic short (low reluctance, similar to low > resistance). It wasn't to 'roll downhill' and sit in a valley and get as > close to the metal as possible.
Of course cogging has to do with the drive waveform, common square wave drives with Hall commutation have large torque (~13%) ripple Magnetic cogging may be noticeble for 2 phase cheapo PC fan motors but certainly not true at all for normal 3 phase BLDC/PMSM servo motors (which have NO dicernible magnetic cogging) I have many PMSMs here from 100 W to 5 KW and _none_ of them show static cogging Peter Wallace Mesa Electronics ------------------------------------------------------------------------------ For Developers, A Lot Can Happen In A Second. Boundary is the first to Know...and Tell You. Monitor Your Applications in Ultra-Fine Resolution. Try it FREE! http://p.sf.net/sfu/Boundary-d2dvs2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
