What is the main function of IGBT in vfd and why failure IGBT in drive what is the reason?

The Function Of IGBT (Insulated Gate Bipolar Transistor) in VFD (Variable Frequency Drive) is high switching speed necessary for PWM VFD operation. 

IGBT provides a high switching speed necessary for PWM VFD OPERATION.

A VFD IGBT can turn on in less than 400 nanoseconds and off in less than 500 nanoseconds

IGBT is a three terminal insulated bi-polar transistor. it is used as the switch in power electronics.vfd will operate and protect and control the frequency of the A.C. input signal.