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Why did my IGBTs burn?

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seyyah

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I designed a 3 phase inverter with 6 discrete 600V rated IGBTs. I applied 10 KHz SPWM to the AC motor(2.2KW induction machine) via the inverter. DC bus is obtained from 380VAC rectification which is @537VDC at no load. I burnt some of the igbts at first try. Then i reduced DC BUS voltage to 300VDC. Tried again at first it didn't burn, but then again. Why is it burning? Due to high voltage at turn off? Do i need a snubber?
I tried the inverter at low voltage (35V) and with a low power ac motor. It worked without problem. But at high voltage, high side is not switching appropriately when dc bus is online. Without dcbus is online, high side is ok. My gate driver is IR2113 based and i tried bootstrap capacitors from 10uF to 470uF. I saw some designs working well similar to mine with low value bootstrap capacitors. What may be the problem?
Please help me because i'm stuck now and don't know what to do and don't want to burn another igbt. Thanks.
 

Why did IGBTs burn?

The IGBT are tolerant to high current but very sensible at over voltage. Usually for 380V power lines you have to use 1200V IGBT and for high power 1700 volt. The voltage spikes caused by commutation (induced voltage on traces and lines from IGBT to your DC line) will be added to your DC rail and easy overpass the maximum voltage.
The PCB layout is very important in order to minimise the trace inductances. Also you have to add low inductance capacitors on DC rail as close to the IGBT leads as possible.
 

Re: Why did IGBTs burn?

Thanks for your reply. Actually i'm doing my project part by part. So every module has own pcb or it's placed on a bread board. Connections are made via cables. So there is no one pcb board. Do small indcutances affect the igbts? Should i place driver and igbts on the same board. Must i add a small high voltage caps accross the dcbus near to the igbts? I think at least it musn't burn with 300VDC. I'd be pleasure to hear all kinds of suggestions to improve reliability and prevent damage.
 

Why did IGBTs burn?

The main problem are not the drivers, but the inductance of the DC bus.
You have to minimise this inductance.
Use twisted pairs of cables from HV capacitors to IGBT's.
Place small value capacitors near the IGBT's on DC bus.
Maintain a decent voltage margin for DC voltage. (use 220V monophase instead 380 V)
Watch with an osciloscope the spikes on DC bus caused by commutation. Try different layout configuration to minimise this spikes.
Use at least a double layer PCB for final product with big zones of ground and DC+ voltage on diferent layers in order to minimise inductance.
If you consider commuting 50A in 10 microsecond on 10 microHenry inductance you will get a spike of 50volt amplitude.
 

Why did IGBTs burn?

Did you provide enough 'dead time' to prevent shoot through problem?
 

Re: Why did IGBTs burn?

Deadtime is ok. I think problem is in gate driver or driver pcb. I changed it and it seems ok..
 

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