Gate Circuit Opend in a VFD??

Case one: Who is still using thyristors in a VFD?

Case 2: If one transistor fails to fire, it affects everything in that you have no conduction in that half-phase for two phase firing sequences. The output would go immediately imbalanced, there would be a very high DC component on the output and the motor would start to fight itself. Most modern VFDs now have a detection circuit that would immediately know that an IGBT was not firing and shut down the entire VFD.

Thanks of the answer, my question now ,is every old SCR phase control circuit can be replaced with IGB control circuit ?

I think IGB works only with DC ?