On Fri, 15 Dec 2006, Jon Elson wrote: > Date: Fri, 15 Dec 2006 21:26:55 -0600 > From: Jon Elson <[EMAIL PROTECTED]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] Mesa m5i20 PWM frequency ? > > Peter C. Wallace wrote: > >> But whats the dead time? If you are not using a closed loop current control, >> (that is the controller PWM runs the HBridge directly) the dead time will >> become a significant part of your 50 KHz cycle time leading to non-linearity >> in PWM versus motor voltage. At least that my experience, high PWM results in >> higher losses with no particular advantages (unless you are running a motor >> with inductive/mechanical time constants so fast that it matters -- perhaps a >> voice coil) >> >> > The internal dead time of the bridge driver is about 100 ns, but the > opto-isolators > are slow, so the minimum output pulse width is about 200 ns. To make > sure the > bootstrap capacitors are kept charged, I require 200 ns off time (not > exactly dead > time, but close) between on pulses. > > The advantage of the higher PWM frequency is I avoid saturation of the > output filter > inductors. Most cheap servo drives do not have an output filter, and > there are many > problems caused by that. Most notably it can cause encoder errors, > which can be > a safety problem as well as just a major annoyance. If I ran at a lower > PWM frequency, > then the filter components, especially the inductors, would have to be > larger, as > the maximum on-time would be longer.
Dont your output filter inductors always have to carry full motor current, regardless of PWM rate? (Well at a really low PWM rate you would have more motor current ripple so the peak current would be higher) > > Jon > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share your > opinions on IT & business topics through brief surveys - and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
