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Micro-grid with MultiPlus II and Fronius Primo - causing flickering lights


We built a new single-phase installation recently with the following components:

  • MultiPlus II 48/5000
  • Cerbo GX
  • 4x Pylontech US2000C
  • PV inverter Fronius Primo 4.0

Grid is connected to MultiPlus AC in, all loads and the PV inverter are connected to AC out 1, like so:


Grid metering is done by the internal meter of the MultiPlus, Fronius is connected via ethernet (zero feed-in with ModBus via TCP).

Generally speaking, this setup works really great, now we're getting to the last 10% of optimization, and the current issue is the transition from grid-parallel to micro-grid, which causes the following:

  • Error 105 on Fronius (AC frequency too high) when switching off the connection to the grid (Fronius restarts/recovers quite quickly though)
  • Flickering lights at certain load constellations while operating on micro-grid (e.g. Fronius delivering 2.5 kW and loads around the same value (oven + small toaster)

The flickering can be described as brightness oscillation around 1-2 Hz, as if MultiPlus competed with Fronius for the voltage regulation. If useful, I can upload a video later.

Parameters are set as recommended by the documentation (MG50 on Fronius, Frequencies set in the ESS assistand according to Native Fronius zero feed-in works fine also. The documentation mentions "Q5 How can I get the Fronius firmware that improves flickering?", but the Fronius is brand-new and all firmwares have been updated, so this shouldn't be the point.

Any ideas and help is much appreciated :-)


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2 Answers
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ips-ad answered ·

This has been solved in the meantime, by Fronius providing a downgrade to fro32071.upd. They said they are aware of the issue and will probably fix it in one of the next versions.

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popnic avatar image popnic commented ·

Just for info. Not solved in my case.

There is no firmware fix available for newest Fronius Primo. 2022 models does not accept firmware version fro 32xxx.upd anymore.

The latest and greatest firmware has some improvements but still not acceptable.

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popnic avatar image popnic commented ·

Thank you for telling us how you solve your problem.

I found that a same setup has same issue. I will contact Fronius.

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Rob Duthie avatar image
Rob Duthie answered ·


The latest ver fro33350 had fixes for MG50-60, but still has issues with flicking.


Rob D


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