On Tue, 18 Jun 2013, propcoder wrote: > Date: Tue, 18 Jun 2013 09:53:33 +0300 > From: propcoder <marius.alks...@gmail.com> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: emc-users@lists.sourceforge.net > Subject: Re: [Emc-users] BLDC - not smooth rotation with hostmot2 and 3-phase > bridge > >> I would not expect very smooth operation in 'D' or step motor mode (no >> encoder >> feedback/PID), especially with IGBTs and their long switching times that >> neccessitate a large dead zone. Do you have the dead zone time set >> properly? I >> think the default is 5 Usec which is (deliberately) huge. (note: too >> small >> a dead time will be fatal to your IRAM) > Same motor, same power supply (12V only), almost the same config, just > MESA 7i39 and motor runs smooth in "n" mode. > If you mean dead time - I set it to 500ns, as I found something like > 400ns at IRAM datasheet. I checked dead time on MESA outputs with scope > and it is correct. > Real switching has a delay of 800-1200ns, but switch-on/off times of > IGBTs are 100-330ns.
Maybe tha actual physical dead time is causing your torque ripple > > 12 volts only - maybe that's the problem? Motors are rated for 48V. > Something about IGBT's? Big resistance maybe? > Will try 48V. IGBTs have a large on voltage (maybe 2V or so) which will add to non linearities. This and the larger dead time may be the cause of this. It could also be a wiring error. Do you have 3 'flat spots' per electrical phase rotation? (1/2 turn on a 4 pole motor) > By the way, what max voltage I can go with this setup when I use phase > current limiting? 600V IRAMs? maybe 450V assuming your isolation, bypassing, and deadtime are right. > >> I would get feedback running before worrying a lot about smoothness. > > Tried "qi" mode with PID (almost the same working config as with 7i39) > too: bldc init passes somehow, but does crazy things due to kinky > movement especially when PID turns on. This is possibly a BLDC setup error. You do need to limit the applied voltage in N mode via "initvalue" since current is only limited by winding resistance. > >> You definately do not want kinks in the top of the voltage waveform. >> if anything you may want a voltage step at the sine zero crossing to >> compensate for the dead zone (if the required dead zone is a significant >> portion of the total PWM period). > My PWM frequence is 12kHz, servo thread - 4kHz. > > So when and why kinky waveforms are used like this > > http://www.postech.ac.kr/ee/cmd/102_BLDC_pedal.htm > ? > No idea unless their motor outputs such a voltage. Spin your motor and look at the generated voltage with a scope. > > > > > ------------------------------------------------------------------------------ > This SF.net email is sponsored by Windows: > > Build for Windows Store. > > http://p.sf.net/sfu/windows-dev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > 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. ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
