How to find relationship between switching energy loss, temperature and current in an IGBT
I usually use spice to estimate switching losses, the first thing I do is make sure the FET model is right, then I calculate the energy from the device and filter it, then use a time constant witch is close to that of the package of the device. The picture below shows a spice energy calculation with an RC time constant:



Another thing that would be useful would be to integrate this with the FET package thermal junction conductivity, but I haven't done that yet, I'm mostly interested in the average ammount of power from a device or FET.