propcoder wrote: > 2013.07.15 21:56, N. Christopher Perry rašė: > >> You should be able to do that. It does make shot-through a little easier to >> manage. Also, there are 3-phase gate drive controllers that will manage the >> gate timing for you. Do a google search for them. Fairchild and IRF have a >> range of them. >> > What do you mean by gate timing? I use IRAM module from IRF. It has > internal protection from shoot-through, it adds dead times by itself. > > Yes, and at the switching frequencies desired for small, fast, servo motors, and with the slow turn-on and turn-off of IGBTs, the dead time may be very excessive.
Here's a little illustration. I built a brushless servo amp using a six-step drive scheme, using the single-chip IR FET driver for all 6 transistors. I had earlier made a brush servo amp using IR's half-bridge driver chip, the IR2113, which is rated at 2 A of gate drive, but actually close reading of the datasheet shows it is more like 1.6 A. This worked well. The 6-channel driver, however is rated at 0.6A, but close reading reveals you only get 200mA for sure! This slowed the turn-on/off of the FETs so much that it really impacted the servo loop performance. I tried a few tricks, like making variants of the amp with big and small transistors, inverse deadband in the PID, and all sorts of stuff, but none of it worked very well. The version with the "big" transistors needed 800 ns of deadtime, which cuts into the total of 20 us PWM period. Then, I made a new version of the servo amp using single half-bridge FET drivers with about 1.6 A drive, and the performance of the whole servo loop was remarkably improved! The main difference, as far as I can tell, was the reduction of the deadtime. I'm guessing with typical IGBTs, your deadtime may run to several us. Fine for a 60 Hz motor drive, not fast enough for a drive that may need to deliver several hundred Hz to a low-inductance motor. Jon ------------------------------------------------------------------------------ See everything from the browser to the database with AppDynamics Get end-to-end visibility with application monitoring from AppDynamics Isolate bottlenecks and diagnose root cause in seconds. Start your free trial of AppDynamics Pro today! http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
