IGBT Problems burnt out problem

[M.Imran Ali]

Hi experts
I have problem , I am designing a buck converter input is 900 volt DC and out put is 384 volt DC . Using TLP350 Driver with 18 / -5 volt .
My problem is that when i exceed input voltage greater than 800 volt igbt burnt with gate to emitter shorted a gate to collector also .
I am using Semikron IGBT skm300GAR128D , That is 300 amp 1200 volt but i not have stilled put load greater than 5 amp .
Operating frequency is 40Khz ......
Please response as soon as possible it is urgent . gate resistance is 200 ohm , i tried 19 ohm , 10 ohm but result same .

 

[FvM]

Did you watch the IGBT waveforms at lower DC input voltage, e.g. 600V? 18V gate voltage sounds a bit high, do you have TVS diodes near the IGBT?

Failure at moderate output currents suggests massive circuit overvoltages due to bad circuit layout or missing input bus capacitor. Gate resistors above some 10 ohms are rarely suitable.

I also doubt that 40 kHz operation at full load current will achieve acceptable losses.

 

[M.Imran Ali]

I have input capacitors but don't have TVS diode across IGBT ?

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Do i need to replace 1200 volt IGBT with 1700 volt IGBT?

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Where to install TVS diode across emitter to Collector?

 

[FvM]

I can tell that 900 or 1000V isn't a problem with bridge modules with state-of-the-art bus bars and bus capcitors. Similarly, presuming SKM300GAR128D is a IGBT/Diode module, there should be a low inductance bus capacitor connected to the bus nodes directly at the module.

1700V has higher overvoltage margin but definitely won't work at high frequencies. You'll rather go towards 5 kHz or so. So I guess it's no option for your design.

To limit overvoltage across the IGBT, active clamping is a usual solution. TVS diodes probably won't handle the energy, at least at higher load currents. RC snubbers may be also used to handle the effects of excessive circuit inductance.

It should be mentioned that in a chopper circuit with overvoltage problems, the diode is the next failure candidate if you limit only the transistor voltage.

 

[M.Imran Ali]

I have 2uf cap between emitter and collector , Please suggest me what can i do to solve my problem?

 

[FvM]

I have 2uf cap between emitter and collector

To achieve what? I don't see how the IGBT could handle this huge capacitive load.

 

[M.Imran Ali]

I used snubber circuit but result is same?