Princeton: This is a picture of extreme ringing of a 400 amp IGBT just before it blew up, because there were no capacitors in the circuit. The capacitors absorb the on-rush of current FROM the batteries when the MOSFETs shut off. The diodes ground out the inductive current from the motor. If you are using the controller as a light dimmer, you don't need the diodes.
I do agree with the use of some zeners or transient suppressors, in parallel with the power diodes, to suppress over-voltages. My controller periodically blows up MOSFETs for no obvious reason. The last time, I jumped in the car, stepped on the throttle, and popped 10 of my 12 FETs. I bought some 180v transient suppressors, that I plan to add.
Also my controller is water-cooled.
