http://powerelectronics.com/mag/504PET22.pdf said:
An overcurrent condition is one of the fatal drive faults
that could destroy IGBT devices in a motor-drive system.
IGBT overcurrent conditions basically fall into three
categories—line-to-line short, ground fault and shootthrough.
Table 1 lists overcurrent conditions and their
potential causes.
When considering an IGBT overcurrent protection
scheme, two important factors must be evaluated.
An IGBT desaturation circuit is the alternative way to
protect the IGBTs. The discrete circuit can be constructed
in the secondary side of the opto gate driver or the optoisolated
device that has a desaturation circuit. The circuit
detects voltage buildup across the collector and emitter
while the device is fully on. If the voltage exceeds a certain
limit, the desaturation circuit shuts off the associated gate
signal. When implemented as a discrete circuit, the required
components are a comparator with voltage reference, a
high-voltage diode, and resistors and capacitors.