Fronius Flickering on AC out - reactive power settings?

DIY
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I have got a (single phase) Fronius primo 3.6.1 inverter connected to the output of a (single phase) multiplus 5kW inverter and the AC voltage is flickering at around 8 Hz. This causes flickering of the lights in the house, which is very irritating and possibly bad for equipment.

I am using an ESS assistant on the multiplus and no other assistants.
The Fronius can provide a maximum power of 3.6 kW and 2 kW of solar panels are connected to the Fronius, but they are pointing at North and at this time of year they will only ever provide a maximum of 1 kW. So the 1:1 rule is satisfied.
Although the multiplus has a (single phase) grid connection, the multiplus is set to invert only (ignore AC in), and a 48VDC flooded lead acid battery of 1000Ah is connected.

I am using an ESS setup provided by Venus running on a Raspi. I have not changed any setting, not that ESS seems to offer many settings.

It seems to be a well known problem that when the Fronius provided power is equal or exceeds the AC loads slightly, that flickering occurs.

The Fronius is connected via LAN, and the Victron VRM portal correctly shows the same power generation as the Fronius is showing on the front page.
The Fronius is configured to use MG50 grid setting.
No frequency control is occurring when there is flickering.
The flickering even occurs when the Fronius is switched on but hardly producing any power at all (18W).

Now to my questions:

It seems to me that there may be some reactive power issue occurring.
I have found a manual for the Fronius to correct this, with the PROFI settings, which I can access because I have the access code on the front panel.
https://midniteftp.com/forum/index.php?action=dlattach;attach=7812

  1. has anybody tried changing the reactive power settings?
  2. If I tried the settings suggested in the link above, would that possibly damage anything?
  3. there are quite a few reactive power modes that Fronius offers. I haven’t been able to find a manual which explains those things in sufficient details. Does anybody know where to find such a manual?
  4. Are there any SAFE things I could just try to see if it works?

At the moment the WAF (Wife Acceptance Factor) is sub-optimal due to the flickering lights.

I have all the latest firmware on all devices.
Fronius Primo firmware 0.3.30.1
Multiplus firmware 552
raspi Venus firmware 3.42

1 Like
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:laughing:

Think a few more details would help to hopefully improve the WAF:

  • Are you having a (standing) Grid Connection, or Offgrid use case?
  • One multi + primo means single phased? Is your house also single phased, or do you just have 2 phases that are “unmanaged”?
  • If grid: does it have a grid meter? Most the time these can be used to also display the powerfactor (cos phi between current and voltage) per phase.
  • is the flickering of 4hz a “subjective guess” or does the data of your MP provide data, showing this?

4 Hz is a ridiculous high offset, that should almost be impossible, while grid is present. (The European Grid will basically shutdown, when going out of 49.5 - 50.2 Hz)

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I clarified the post a bit: yes it is a single phase grid connected multiplus but the AC input is set to “ignore AC” and “invert only”, so for all intents and purposes the mode it is in is basically off-grid.

I have added some pictures which I have taken of the AC out of the victron with an oscilloscope.

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You can see from the pictures that there is a recurring wave with a duration of 8 sine wave peaks, or 160 ms long. The delta V equals 34 VAC peak to peak, which is modulating the 240 VAC RMS output. So the modulated wave has an amplitude of perhaps 10%, or plusminus 5% if you will.

An extra bit of information: whilst this flickering is going on the Fronius is happily showing a 0 VAR out, whilst it is supplying 300W power.
I do not know if that means that there is not some reactive thing going on which can still be solved by making some changes in the Fronius.
Previously I had an old grid tie SMA sunny boy inverter (2kW with 1kW of panels) hooked up to the output of the multiplus instead, and it produced far less of a flickering effect.

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No I do not have a power meter between the Multiplus and the house, or between the Multiplus and the Fronius inverter.

I have seen them on ebay for 13 GBP so whilst I do not want such a chinesium part to be permanently in my setup, I am considering to buy one for diagnostics purposes.