What causes unbalanced output in an inverter?

[Arifur]

What is the basic reason of unbalance output of an inverter, even the output connection is open and the IGBT is ok.
Can anybody tell me what is the problem?

Co operation is always encouraged.

 

[Hesch]

Can anybody tell me what is the problem?

It's impossible to locate/suggest an error without a ( sketch of a ) diagram:

Analog/digital, PWM-output, detailed symptoms, whatever?