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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hi Furnace, thanks for your PM, which I do my best to answer here.
I'm no expert in these things, but if that is indeed the signal measured off your gate, then we must ask what it is, and where is it coming from?
What is the frequency of that strong sine wave? Is it at your mains frequency - 50 Hz or 60 Hz - or a multiple of it?
If you look at the tops and bottoms of the rough square wave, you'll see it isn't flat, but takes the form of a train of damped waves. You should count the number of peaks on these waves, and work out their frequency. Where are they coming from? Some kind of 'ringing' perhaps?
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
Location:
Posts: 108
Thanks for the help guys.Proud mary the wave signals you see is measured with the scope at the negateive of the igbt or the inverter and at the one end of the tank. Im running at 40khtz phase shifted. At the moment i cant do any testing because i killed one off my tc chips, so i had to order new stock from digi key which will only arrive on tuesday. I will definitly try the batery ash small to see if the problem can be eliminated this way because i also think that it can be a ripple in my dc regulated supply.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
It looks to me like parasitic oscillation between leakage inductance and the gate capacitance of your bricks. It looks a lot slower than most of what you see normally, probably because you don't usually see this occur with igbts that large. Could you post a picture showing the igbt bricks and their connection to the GDT?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
furnace wrote ...
I will definitly try the batery ash small to see if the problem can be eliminated this way because i also think that it can be a ripple in my dc regulated supply.
Personally I think Ben is on the right track. I just suggested using a battery so that you can eliminate the power supply as the source.
You need to eliminate as many possible causes as possible first, before you start speculating, etc. But trying a battery will eliminate the power supply (I expect), then we can look elsewhere. Also, you need to be certain your power supply is ok.
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
Location:
Posts: 108
The oscillation is already there before the gdt is connected to the brick so it starts from my 2 tc chips and it just gets worse when i start giving power to the inverter.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
furnace wrote ...
The oscillation is already there before the gdt is connected to the brick so it starts from my 2 tc chips and it just gets worse when i start giving power to the inverter.
Is the ringing there before you connect the primary of the GDT to the tc drivers? If the tc gate drive ic's have a clean wave on them when left floating, but then get sloppy when the GDT is connected(bricks connected or not) then you have to look into primary side ringing. could you show the connection from the ic to the gdt? What do you use for the value of your dc blocking capacitor?
Registered Member #4992
Joined: Wed May 23 2012, 03:57PM
Location:
Posts: 108
Yes its already there before the primary of the gdt is connected and i have 1uf cap connected on the primary.So when the tc chips float the signal is not clean. It starts there already.
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Gate drive signal
