It is designed to generate ac output of 27 levels/ phase. Three H bridges are used with three unequal distributed DC sources (1:3:9). "A" represents the no. of level in the output and "F" indicates the output frequency. Sinusoidal PWM used to vary the output voltage and frequency. So the model can be used for other applications like drives, DVR, grid tied inverter etc.,
Need information on designing pulse generation circuit.
I did not understand how this circuit generates 27 levels. We have 3 dc sources. So number of levels should be (2*3)+1=7 [2s+1....where s is no of dc sources].