In message <[email protected]>, dated Wed, 8 Nov 2006, David Cuthbert <[email protected]> writes >I can see using a PLL with a long time constant to obtain immunity from >line noise. But If the line zero crossing shifts abruptly the SCR fires >to one side of zero crossing.
It's unusual for the zero-crossing to simply shift. It's more common to get one or more spurious extra zero-crossings, and the PLL ignores them. That does increase the harmonic current emissions, since the voltage may not be exactly zero at the switching instant, but there doesn't seem to be any way to prevent that. If you try to gate out the switching pulse if the actual voltage is too high at the predicted zero-crossing instant, you may miss complete half-cycles, which is a much less attractive 'feature'. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk Swine wave - a waveform whose spectrum is exceptionally difficult to calculate. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
