When you are designing inverters with IGBTs there are a few key things to worry about. You already discovered the big one, which is the timing of the high side and low side IGBTs on the same output leg. If you turn them on at the same time, or turn one on while the other is still in the process of turning off, you get a very high current through the two of them. This is called "shoot-through" and is definitely something you want to avoid. Remember that IGBTs have resistance measured in tenths of Ohms and your capacitor bank and the traces/wires between it and the IGBTs will be very low impedance by design... That's a lot of energy with an ideal short-circuit path. On a 208V inverter design you might have a 340V bus and a half an ohm IGBT on-resistance ... you get the idea.
If you are using a DSP with any kind of motor control enhancements, there will be a few extra settings to play with on the PWM peripheral. You'll see options for tuning how much dead time there is between PWM outputs, tuning the delay before and after the midpoint of the PWM pulse, and there may also be additional inputs to detect things like de-sat or excessive current.
In my own inverter designs I tended to put the de-sat detection in hardware, as my almost two decades of experience has taught me not to trust software. :-)
Another very critical thing, and one that is not quite as critical anymore with the more advanced PWM controllers, is that the high-side driver and the low-side driver must be balanced. If it takes 500us for a gate fire signal to propagate to the IGBT on the high side, you must add additional delay to the low side (the low side driver is generally a simpler and thus faster circuit). As I said, high-end PWM controllers allow fine-grained control over each PWM output and can unbalance the firing so the hardware side is simpler, but being the old fart that I am, I still think it's good design to have the timing on both sides matched.
When testing, I strongly suggest some kind of fast fusing and even reduced current on the bench. IGBTs can be damned expensive, the magic smoke they let out isn't good for your lungs and the noise they make isn't good for your ears. Wear proper protection equipment and always be fully aware of the lighting that lurketh in a fully charged capacitor bank. Inverter design mandates that you minimize impedance, which just makes the accidents all that more spectacular and dangerous.
Addressing your questions in order:
The IGBT will not be impacted in any way. IGBTs do not conduct current in reverse; this is why they must be coupled with a separate diode [1]. Even with the IGBT on, its free-wheeling (also called 'anti-parallel') diode will conduct the current. MOSFETs, on the other hand, can conduct in both directions. In the MOSFET, the current can reverse-conduct through either its channel or its body diode, depending on the current, channel resistance and body diode drop. The body diode is inherently built into the MOSFET.
It will indeed be turned on, but no current would flow since the collector would be floating. An IGBT, like a MOSFET, turns on gradually. It begins to turn on when the gate voltage exceeds a threshold, relative to the emitter.
Yes to both. The ratings you mention (10A, 600V) are the maximum ratings. You can use the IGBT with 25V bus and 500mA, no problem.
[1] See an example of a TO-247 device which is effectively an IGBT and diode co-packaged: http://www.power-eetimes.com/imf/c/eyJtYXNrIjoiNDMyeDI4OCJ9/images/01-edit-photo-uploads/2014/2014-06-june/onsar2662_fig-1.jpg.
Best Answer
There are tests you can perform to gauge the "health" of a module. Essentially you need to characterise a number of healthy modules. The minimum number of failed devices essentially comes down to device tolerances and measurement accuracy.
What you need to consider is what types of failures are you looking for?
There are four characteristics worth determining for the complete module
An IGBT die datasheet will usually provide the small signal \$C_{iss}\$, \$C_{rss}\$, \$C_{oss}\$. You cannot just take these values and multiply them by 200 as there will be additional stray capacitance within the module under test.
Once these values are measured & captured for a number of healthy modules, you will be able to determine a spread. The number of failed devices you could possibly detect then comes down to the deviation. The loss of one device may still fall within the possible healthy range. 2? 3? once you have some empirical evidence you can come up with a detectable number.
The final method is to mount the module on a heatsink and heat the heatsink to a given temperature (50C, 75C). A significant temperature above ambient to mitigate change in ambient when testing on different days.
Gate ON the IGBT stacks (9V or the correct 15V) but ensure you measure the gate voltage with reasonable accuracy (not a 9V battery when it is really supplying 8V...). Then with a high current source with a resistive shunt to measure the forward current accurately, apply this source Collector --> Emitter.
Measure the Collector->Emitter voltage. The actual current to be applied should be say... 50% of the maximum device current. With the loss of one or many devices this \$V_{ce}\$ will rise.