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. 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
