Hello everyone
I am doing my final electrical engineering project. I am building an induction furnace using a full bridge IGBT inverter. I am using an IR2110 high/low driver as well as dual channel optocoupler for isolation purposes.



I have encounter a problem when testing the inverter at no-load. A large ringing occurs at the flat tops of my inverter output. At this stage my IGBT's do not get hot when running at no-load, but the ringing does prevent me from pushing higher voltage through my DC bus.



I implemented a C-snubber and found that the ringing went away the larger the capacitor over the emitter and collector of the IGBT's. What i noticed was when the ringing went done, the IGBT's became hotter even at no-load.

The yellow curve is the current measured through the conductor between my DC supply and the DC bus terminals on my inverter PCB. The blue again is my inverter output at no load. The yellow is a bit concerning seeing that no load is attached. I have significant amount of deadtime also implemented through my stm32. After presenting this problem to my study leader, he suggested that I implement a diode between my DC supply and DC bus on the inverter. I implemented it and found that the ringing at the my flattops disappeared.

Now my IGBT's get hot and the diode also starts to heat up. I don't want to push the DC voltage to much because the current increases with it(see yellow curve). I am lost as to what can be the cause for these losses being generated by the IGBT's. For additional information below is my gate to emitter voltage waveform and looks like there is no shoot through between the two complementary signals from the IR2110 and the optocoupler.


Any suggestions will be appreciated.
Thank you in advance.

 

Welcome to AAC!
You say you are using IR2110, but the schematic shows IR2113. Which is correct?

 

Hi Alec, pardon I am using the ir2113. Both 2113 and 2110 are the same but rated for 600V and 500V respectively.

 

The snubber capacitor across each IGBT *must have* a series resistor.
Otherwise while the IGBT is turning on, meaning the linear switching portion where power dissipation is very high, the capacitor will discharge adding to the heat dissipation.

There are other snubber configurations, which add a diode in parallel with the resistor, to further improve performance.

 

When I added an RC snubber to the IGBT's, the response became like this (ignore the yellow curve). I play around with resistor values between 10 and 100 ohm in series with a 100 nF capacitor. The response stays the same with varying ringing voltage variations. Any reason why that might be ?

 

To compare apples to apples, you MUST show sthe Vds waveforms showing the different snubber configurations, without changing any, nada, none of the scope settings between one image and the another.
These settings, in addition to the timebase and vertical scale, include the acquisition type, the trigger level and type, and having the reference cursor always at the same level. The only thing that you are going to touch is the delta cursor.
Remove extraneous (the yellow waveform), simply turn the channel off.

Since some changes will be very subtle, the best approach is to take the first waveform, store it in reference memory, and then take the second waveform and overlay it. Make sure the reference gain and offset match the primary waveform.

Lastly, make sure that your probe is properly compensated before taking any high speed waveform.

 

At that frequency it is usual to use Mosfet at that freq. not IGBT PWM which are recommended at much lower switching.
Also see Tahmids blog on the circuits https://tahmidmc.blogspot.com/2013/01/using-high-low-side-driver-ir2110-with.html.