Re: Recent s.s.t.c work

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>



> I invite comments from the List

Yeeha! Go for it KC!


> Perhaps someone has an opinion as to whether that's fast enough to save a 
> brick in the event of full upper:lower conduction.

I think you are mighty brave to actually try and incorporate shoot-through 
protection. Any protection is probably better than what we have just now.

The problem you'll run up against with this design is stray inductance of 
the current sense resistor. You wrote that it had a resistance of 0.001 
ohm. So the reactance at the operating frequency ought to be less than that 
or you'll get spurious triggering due to L*di/dt voltages.

If you're running at 50kHz then Xl=0.001=2pi*50000*L so L=3.2nH, good luck!

And the same goes for any mutual inductance linking the power circuit to 
the wires that connect the shunt to the sensing circuit. This is one reason 
why we tend to use CTs and Rogowski coils rather than shunts. In your 
existing circuit you could use a Rogowski coil in series with the sensing 
wires and adjust it to "buck out" the stray self/mutual inductance.

Finally, there's a philosophical question here. If your driver circuit is 
reliable it should never cause shoot-through by misdriving. So the only 
situation that will cause serious shoot-through is if one IGBT in the arm 
tries to turn on into the other one that has failed short circuit. Now, 
those IGBTs come two to a package and if one has failed the whole package 
has to be thrown away. So who cares about saving the other one? Just my 
opinion of course. I could probably be persuaded otherwise.


> The photo shows my primary: 6 turns of paralleled 1/4" Cu tubing wound 
> inside an 18-gallon plastic bucket.

Neat!


Steve Conner