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marekp avatar image
marekp asked

Why AC-coupled Fronius is FQ shifted OFF when only one phase is missing?

Strange situation.

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?


phase.jpg

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.

screen-shot-2022-04-09-at-83406-am.png

And here the proof.

After disconnecting my system from grid completely, Fronius started producing.

screen-shot-2022-04-09-at-84702-am.png

AC PV Coupling
phase.jpg (154.6 KiB)
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shaneyake avatar image shaneyake commented ·
Are you using DVCC? Does your BMS have coms with the GX?


Can you post a picture of the Battery voltage and current?
As well as the CCL and DCL values?
You can post a comment with more images.

Your system looks to be frequency shifting, back and forth a bunch. Which could be a BMS related problem.

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3 Answers
Alexandra avatar image
Alexandra answered ·

@MarekP

Just a thought, but frequency shifting control will be a little messed up as working on grid and offgrid is different, and you now have a mix.

Maybe you would need to have switched as a group on? Then all switch to inverting when one phase is off. Unless you have a reason why they are not switching as a group?

I could not say for sure as I have never experienced this scenario.

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marekp avatar image marekp commented ·

@Alexandra

Thank you for your input.

I do not understand this system behavior.

When 1 phase is missing the system should, as a whole, switch to inverting.

AC-coupled Fronius should produce since there are loads and battery has allot of room to take energy.

But system is shifting FQ to the point that makes Fronius to turn OFF.

In my view, the system should ignore the remaining phases and act as there is no grid.

When in inverting mode the input relays should be OFF, aren't they?

If they are, there is no ON-grid situation for the reaming phases.

In my original post two pictures are missing.

The showed the different behavior when only 1 phase is missing and all phases gone.

For some reason I cannot insert them again.

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Alexandra avatar image Alexandra ♦ marekp commented ·

Ess is loaded onto all phases so when one phase falls away, ess on that phase is not in control. The mix will be the issue, I would think anyway.

Are you able to fake a single phase dropout with L1? See if the same error happens.

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shaneyake avatar image shaneyake marekp commented ·

In VE.Bus System Configure make sure you have switch as group ticked.

If switch as group is ticked and you lose a phase it will bring the complete system off-grid.

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marekp avatar image marekp shaneyake commented ·

@shaneyake

Thnak you for the tip. Will check it tomorrow.

But when I look at a voltages in AC input phases and AC output phases, on AC-input I can see which one is missing but on the AC-output all phases are generated by inverters (They all have exactly 230V) from the moment one phase switched off.

Is it not the indication that all inverters are OFF-grid from the moment one phase switched off?

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shaneyake avatar image shaneyake marekp commented ·
Does the input current drop to Zero on all phases? If they are disconnected it normally goes to a perfect 0 vs slight up and down when connected. That seems to be the most reliable way for me to see if connected or not.
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marekp avatar image marekp shaneyake commented ·

@shaneyake

YES, all 3 phases show 0A current from the moment the L3 is gone.

You can see it for phase L1 on the picture I inserted in the first post.

For some reason I cannot insert any more pictures, :)

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Alexandra avatar image Alexandra ♦ marekp commented ·

@MarekP

I saw that, it seems grid rejection and grid faliure/blackout mixed have the undesired frequency too high error (105). But the frequency is at 52.9hz. 53 is the disconnect.
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marekp avatar image marekp Alexandra ♦ commented ·

@Alexandra

That 52.9Hz is just resolution error.

Believe me, Fronius is off completely.

With total disconnect there should not be this FQ shifting.

I tried to ask Victron, but they are not answering my question.

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Vangelis Beligiannis avatar image
Vangelis Beligiannis answered ·

Hello. I have exactly the same problem with 3 multiplus Ii48/8000 and a fronius symo. In my case it is even more strange as the output frequency is 50Hz and I still get the 105 error for overfrequency. When i switch off all phases the error goes away! I contacted fronius and they said it has to do with the Victron output. If you contacted victron and they did not answer, it means they have no idea. I will get back if I find something.

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marekp avatar image marekp commented ·
@Vangelis Beligiannis

Try asking Victron service. Maybe they will take it seriously when more than one system is affected.

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Vangelis Beligiannis avatar image
Vangelis Beligiannis answered ·

So back to the problem with more details.

The Fronius inverter will show the error 105 when phase L2 or L3 are lost.

If L1 is lost than the inverter operates normally.


I contacted my dealer as well.

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marekp avatar image marekp commented ·
@Vangelis Beligiannis

Victron Service answered my question, and the way my system works i perfectly normal. They may work on this in the future but now it is not a priority.

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