[dcb]

I would separate your safety concerns from the control concerns. $7 is cheap compared to some of the current sensors our there and the time required to turn it into a dynamic fuse.

Also, derate the IGBTs, and heat sink them, I wouldn't expect a 30 amp igbt to be happy at a constant 30 amps.

Look at the igbt datasheet to see if it has built in diode protection and gate voltage requirements.

And consider using two spdt switch to control them, that ties the gate to ground or 15v (check datasheet) source, just to keep it simple, safe and reliable, where off means off, with a low gate resistor so they turn on/off quickly. You can also tie it into the high side of the pack easily with spdt.

You will want a tiny bit of delay between turning one off and turning the other on (to ensure the igbt has actually turned off). A simple mechanical interlock (sliding bar) on the switches that only allows one switch on at a time would provide plenty of delay for the igbt to turn off and also allow you to turn them both off. So it goes, turn off pack 1, slide bar, turn on pack 2.

I don't understand why you need 4 switches? You have two packs and only need to switch one leg of the pack in or out. Switching both legs is inefficient and not common practice.