How a AC to DC Inverter works

**broken link removed**I am wondering how exactly the attached drawing works when the inverter is supplying DC from AC. (Only one of three shown)
The Insulated Gate Bipolar Transistors (IGBTs) are configured to supply the Negative DC Rail first when they are fired, so how do we get the positive DC supply?
I am happy how the IGBTs are fired and how it works to give out a 3 Phase supply but not the other way.
The drawing is missing the flywheel diodes in parallel with the IGBTs.

Your diagram misses a very important point: Where is the other AC line connected relative to the Power Supply's Load?