Today one phase (L3) in my 3-phase grid vanished.
System switched to inverting but AC-coupled Fronius immediately reported state 105 and switched off.
I did not expect this since battery was at 57% SOC, loads where around 900W and expected Fronius's production should be around 600W (it was 10AM and cloudy). There was no need for FQ shifting. I calculated the expected Fronius's production from MPPT production that was going on without problem. MPPT was producing 360W and there is 10/6 power ratio between Fronius and MPPT.
At that point I switched grid off with the main switch. Now all three phases are gone.
Fronius restarted and begin producing as much as expected.
Around 3PM I flipped the main switch back on to see if the missing phase is back.
Immediately Fronous stopped with the "ERROR" on the display and refused to turn on production with the state 105 reported. (Phase L3 was still missing)
Turning the main switch off again "fixed" Fronius's problem and it started producing.
My questions are.
When system switches to inverting because 1 phase is missing how this can influence the AC-coupled Fronius?
What is different between 1 phase missing and all 3 phases missing?
Obviously something is different, but what and why?
Can someone explain to me, why is my AC-coupled Fronius frequency shifted now to the point that is completely OFF?
There is enough load from the house and half of the 20kWh battery waiting for the energy. MPPT chargers are working and Fronius should produce almost 800W with the sun available.
I think there is a bug in the MP-II firmware or ESS assitant that prevents AC-coupled inverters from producing when only one phase is missing.
And here the proof.
After disconnecting my system from grid completely, Fronius started producing.