[SOLVED] High Side IGBT breaks down in Inverter

I am trying to make a simple switch mode PWM inverter rather UPS for my own. I have completed the work and got the output but there is a problem i occasionally face that the high side IGBT breaks down. It happens occasionally not always. I even use my inverter perfectly for weeks but then....... It works fine even with full load of 800W without heating up. May be i m missing some kind of Snubber or a filter capacitor which is needed for safe operation of high side IGBT. I have replaced IGBT with MOSFET (2SK2611) but the result is exactly the same. And if anyone can help then do tell me that does a ground side IGBT needs the same safety? Can anyone help....???? The diagram is attached in the image

I'm rather surprised it has worked all this time with no snubbers.

RC snubber should be enough. i'd also suggest you make a more robust gate driver.

I just had more research about snubbers. What will u suggest in this case "RCD clamp snubber" , "RCD charge discharge snubber" or simply an "RC snubber" and what can be the estimated values of R and C for 50Hz for total maximum power output of 800 W

If the DC-bus is correctly bypassed, H-bridges won't need snubbers, I think. But kOhm gate driver impedances can't control IGBTs reliably. You should at least have a pulldown transistor to keep the IGBT safely off, when the other transistor is switching. I don't understand the purpose of gate AC coupling in your circuit, by the way.

Hi,

I think that instead of the 10uF series capacitor (I can't understand why you did this), you should just use a 10R or 22R resistor. Instead of the 10k resistor from gate to ground, use a 1k resistor. The 2.2k resistor is not necessary if you replace the 10uF cap and use the 1k resistor. You can add snubber, but I don't think that'd be the cause of the failure. The snubber can be a simple RC snubber circuit.

To make the turn-off better, you could have an additional transistor that pulls the gate to ground, but for low frequency (eg 50/60Hz) this is not an absolute necessity and you may get away with just a pull-down resistor.

Hope this helps.
Tahmid.

I added RCD clamp snubber on Q1 and Q2 and testing it gave an intresting result. This time Low side IGBT broke down (twice as i conducted). Then i made the gate drive more robust without a coupling capacitor and zener protection. After that; till now its working fine......... Lets see

I tried snubbers but then i realized that the problem was not at all about snubbers, strong gate drive is the reason, i modified it simply on my same pcb as in the picture and it works very fine. 100R ground resistance and capacitor make it very strong. But i got the ultimate result when i used the winding of a pulse transformer as gate drive which takes the gate to negative during off time but the restriction there is about PWM which is not possible there. With pulse transformer i used 10uf/35V capacitor on gate to remove noise. But later on i further found that the switching relay of UPS also creates problem while switching and a back pulse breakes down the IGBT, i think the possible solution is to use a relay of better quality or use small capacitors on the points of relay to avoid sparking bw the points, but i havent tried it yet..... but as far as only inverter is concerned the prblem is only solved by strong gate drive