This circuit is likely a modified sinewave inverter (three step AC output) using only a push-pull transformer. When output is suppose to be zero both (Q14,Q28) MOSFET's turn on to short the transformer at winding 9-2 to ensure output remains at zero volts. It can also act as an active snubber. The two diodes, along with MOSFET inherent D-S diodes, form a full wave rectifier that provides input to mcu for overshoots to trigger both MOSFET's on.
Somewhat more complicated then just using a H-Bridge output driver but transformer eliminates separate DC-DC converter. Reduces overall inverter major parts by two MOSFET's. It requires a large low frequency transformer. There are UPS supplies that use H-bridge drivers on battery side of low frequency transformer.