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Registered Member #3640
Joined: Sat Jan 22 2011, 12:16PM
Location: Germany close to Heidelberg
Posts: 39
Dear all, since a while I am kind of obsessed of the different ways of introducing phase lead to a driver. For the people not familiar with the concept: This is about circuitry to trigger the switching of the IGBT in advance of the zero current time, so that the combined delays of driver circuit and IGBTs are compensated, so that the switching really is as close to the Zero current time as possible.
Ways I have seen so far or theoretically thinkable: 1) Using a PLL - e.g. like Steve Conner 2) Using a parallel inductivity to the CT - like Finn, Steve Ward or Reaching aka CTC did in their predictor/UD2/etc. versions 3) Using a FGPA - e.g. like Tsar is working on 4) Using a mikro controller - e..g the Picollo uC from TI (powerfull piece) 5) Using DDS (Direct Digital Synthesis - not seen yet, but should be possible (had a recent thread on it with limited feedback). 6) and lastly an All Pass Filter - something mentioned by GeordieBoy long ago in some thread.
Esp. number 6) seems so simple, that I am surprised that noone seemed to have tried this before. I tried a simulation in LtSpice, attached for your review. Need to buy some fast OpAmps, then I'll try on breadboard. Adjustment should easily possible via R3 or R4.
What other potential ways to introduce phase lead might exist? In particular looking for simple options which would allow to keep delay compensation independant from frequency. 3), 4), 5) would allow this, but are complex. ]phasenschieber_tl072.zip[/file]
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
I am working on the same! Going a different approach though. I am working with the switching circuitry from a miller tig welding machine. It is capable of switching 300 amps dead on the zero crossing at a 60 to 70% duty cycle. 24 volts, however, that is what i am working out how to change!
So, MORE POSSIBLE!!! Gotta love the scavenger approach!!
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
I'd be a little concerned about the circuit in your simulation, it looks like the shift error on the first cycle is huge, much worse than the first-cycle error on a parallel inductor CT.
Registered Member #3640
Joined: Sat Jan 22 2011, 12:16PM
Location: Germany close to Heidelberg
Posts: 39
You are indeed right. I simulated a conventional circuit with a parallel inductor, and it's significantly better. Both simulations are added again (I measured the differences out).
Question now is, why is this. Bad dimensioning of the all pass, or wrong parts?
]feedbackschaltung_phase_lead.zip[/file]
Dr. Electron, what's the circuit used in your welder case for phase lead?
Registered Member #4084
Joined: Sun Sept 04 2011, 10:51PM
Location: Germany, near Gelsenkirchen (FC Schalke04)
Posts: 4
You can use LVDS Linedrivers. That are damn fast Amps. I use them in my ZC-Detection, but you need a good filtered powersupply or they will start oscillating. I dont have the exactly Type in mind, but they are some MAXIM drivers and work quite well up to 250MHz I use them at just 50kHz.
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6 different Methods of introducing phase lead to DRSSTC drivers. More possible?
