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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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1 Answer
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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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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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