OK, well I'll give it a go.
Don't think of them as "transistors"... since they're operating as an ideal switch, think of them as contacts for a relay. Ignore the BJT transistor look and draw in an open relay contact... -||-
Let's call the "transistors"
A B C
D E F
Then we have legs 1, 2, and 3 of the motor.
Close A and E. You now have 679 volts between legs 1 and 2.
Open A and E and close B and F. Now you have 679 volts between legs 2 and 3.
And round it goes...
Does that help?