Three Phase Inverters fed by renewables parallel with main grid

Inverters in parallel

There is a microgrid consists of renewables and battery-bank that provide power by three phase inverters.
each inverter in either isolated or connected mode operates fine but when inverters are parallel they don't operate.
The two first files are two inverters individually connected to main grid, and the third is whole grid with two inverters and main grid. there is also an image of grid.
Can any one explain why it does not work when two inverters are in parallel?