What specifies how much energy can be disspated in an IGBT when switching off?
A general bit of advice for reading data sheets. If you're looking for (let's say) the power consumption, which will be in amps, or the gain bandwidth product, which will be in Hz, it's far easier to run your eye quickly down the righthand 'units' column, looking for the relevant unit, than reading down the left hand measurement description column.

This energy dissipation will be measured in Joules, and it's about the only specification in those units. It's called either the 'Unclamped Inductive Switching Energy' (UIS) or the Collector-Emitter Avalanche Energy.

As the inductor current is interrupted, the voltage will rise. The IGBT structure is fairly robust, and avalanches stably at the breakdown voltage, as long as the energy dumped (assumed adiabatically (that is instantaneously, without any heat loss to the surroundings)) into the junction is limited to limit the temperature rise.

This example IGBT is a fairly small one, 20A 400V, designed for car ignition. It has a single pulse CE avalanche energy of around 400mJ. You might expect the spec to more or less scale with IGBT current, so it looks like you're looking for a >>1000A part before you start seeing 10s of Joules specified. This might be reasonable if you have a 300A load.

If you want to switch the current off quickly, then you need to allow the voltage to rise, and the higher the better. There are alternatives to dumping the energy in the IGBT junction. 

The simplest is to put a resistor plus diode in parallel with the inductor. Arrange the resistor value R2 to develop a bit less than the IGBT's breakdown voltage at the inductor current, so that it limits the voltage across the IGBT. The current will not stop as quickly as for using a constant voltage breakdown mechanism, but heat in a big resistor is a lot easier to handle than heat in a small semiconductor junction.

A faster way (more time-averaged voltage provided) is to charge a capacitor C3. If it's big enough, the voltage will be fairly constant during the pulse, and it can be steadily discharged by a low power route, R3.







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