In industrial application, VSI is mostly used, because a wide range
of speed control is possible. Three phase VSI is operated at two modes i) 180
degree mode operation and ii) 120 degree mode operation. In 180 degree
mode of operation three switches conduct at one cycle, each IGBT is operated
at 60 degree delay angle. In this mode of operation, one can easily get the
pure sine wave using a filter. So it is otherwise called as a quasi square wave
mode or switched mode (Ned Mohan et al 2009). In 120 degree mode
operation is pair of switch conduct at 120 degree delay angle. In this mode a
shoot through fault occurs.