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link-cat avatar image
link-cat asked

Offgrid 3 Phase with AC coupled 3 phase

I wasn't able to find the answer on the forum and in the manuals or Victron unlimited.

I'm planing for a 3 phase completely offgrid situation with 3 units of MP 10k. Will be adding a Fronius 20kw 3 phase PV inverter (or 3*MP2-15kva+1 Fronius ECO 27kw)

As it would be disconnected for the grid, I suspect the MP are going to do frequency shifting (instead of Modbus communication). That's ok (not ideal, but ok).

All the house/shop will be on AC-OUT. If the batteries are full, the MP's will increase freq to stop the Fronius (in all 3 phases).

What's going to happen if L1 has a load? As the frequency shifting applies to the PV inverter, all 3 phases will be shut down. If L1 has a load, the idea scenario will do that the Fronius deliver power to that load (L1 1500W, L2 0W, L3 0W). But I've no idea if it works like that (specially if the communication is via freq. Shifting instead of Modbus).

I suspect (hope I'm wrong) that the MP on phase 1 is going to invert from the battery, and as the battery gets drained, the frequency shifting will decrease, starting again the Fronius, to recharge the battery (AC-DC). In this case, is not ideal, the battery will be most of the time playing between 100% to whatever takes to restart the Fronius.

Cheers

Modbus TCPoffgridAC PV Coupling3 phase
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2 Answers
Alexandra avatar image
Alexandra answered ·

@link_cat

it wont increase to stop production entirely, but the fronius will run in a throttled state.

Fronius do prefer to have balanced loads though so you may find it throttles under the load.

Hope you have plans for a DC mppts if offgrid as well. A combo is most ideal.

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link-cat avatar image link-cat commented ·
Hi, do you know where can I find the details or manual about this? Haven't seen it on webinars or victron professional.

I can't understand why it shouldn't stop completely if the battery is 100% and there are no loads (where the energy goes then...?)

The ideal scenario will be the 3 phases with similar load, but it isn't always easy.

Thanks for the suggestion on the mppt side, yes, there are 4 250/100 on the list.


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Alexandra avatar image Alexandra ♦ link-cat commented ·

You post mentioned a small load on one phase with a full battery. I can confirm during a power cut, the fronius on three phase runs throttled and balanced production over the phases.

The frequency shifts up and the fronius runs in throttled state- it reports this to the vrm. That is how the mechanism works.

But having a small amount of DC mppts is also a good idea.


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link-cat avatar image
link-cat answered ·

Hi, do you know where can I find the details or manual about this? Haven't seen it on webinars or victron professional.

I can't understand why it shouldn't stop completely if the battery is 100% and there are no loads (where the energy goes then...?)

The ideal scenario will be the 3 phases with similar load, but it isn't always easy.

Thanks for the suggestion on the mppt side, yes, there are 4 250/100 on the list.

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