I may have a potential thermal issue with 1 IGBT in a 6 pack configuration for 3 phase AC inverter. The IGBT has a self-shutdown thermal protection and it looks like it is faulting the device into shutdown temporarily. Not sure if its from Conduction losses or switching losses?
How does an IGBT have thermal shutdown...? Unless you mean it's built into the control circuit. Does the 6 pack of an integrated NTC?
You can't really get a decent measurement of switching losses. I know people in industry who are able to actually plot current and voltage through each IGBT with enough bandwidth and memory to do a direct measurement, but it takes a ton of specialized equipment which I'm guessing you don't have.
First I would try a spreadsheet method where you look at one full cycle (that is a motor rotation cycle, not a PWM period) for one IGBT. Actually you should only need 90 degrees of a cycle, not sure for a 3phase inverter. Break it up into a bunch of discrete time points (you don't need one for every PWM period). You should know what the average leg current for that IGBT at each point, so you should know the turn on and turn off energy for the IGBT (if you read the datasheet closely), and the energy lost each PWM cycle due to conduction losses (since you also know duty cycle). Multiply all of these by your average PWM frequency and that should give you your average power loss.
This method sounds tedious, but was extremely useful to me once when I was designing a high power PFC supply. It turned out that power dissipation was about twice what I expected due to large recovery currents from my catch diodes. Also I realized that the thermal impedance of my IGBTs and thermal pads was higher than expected.
I've attached the last spreadsheet I did, which was with a f450r12ke3 IGBT six pack (but we didn't use it as a 3phase inverter, rather we were making an interleaved PFC boost converter, so you'll need to revise it somewhat). You can see how we did rough linear curve fits for the switching and conduction losses, taken from the device datasheets. Sheet 2 has the actual table which calculates the losses at each time step over 90 degrees of an AC cycle. Also includes estimated thermal impedance to give an estimated temperature rise.
If after doing the spreadsheet you're convinced that you're still getting more dissipation or temperature rise than expected, I would then take a scope to the system and see whether you're getting rise and fall times that match up with the IGBT's datasheet. Also consider that you may have poor thermal conduction.