Multiplus II ESS with Fronius Gen 24 on AC out

Q&A and troubleshooting
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1

I have a 3 phase 50 Hz power grid with 3 x Multiplus II 5000/48 set up in an ESS configuration, with a Fronius Gen 24 coupled on AC out. I have a battery bank of Pylontech US 5000 of 8 x4.9 kWh, configured corectly as per Victron-Pylontech configuration page. Pylontech BMS communicates via CAN bus with Victron ESS.

Fronius in configured corectly on MG 50 with solar API toggle on. Victron ESS comunicates corectly with Fronius.

When the grid goes off, Victron ESS switches to offgrid and Fronius continues to stay online an feed into the microgrid and the batteries / AC loads.

When I did these tests the baterries were at 45 % SoC, Fronius was generating about 2 kW.

THE PROBLEM :slight_smile:
When the grid comes back, Victron reconnects after the 30 sec (set grid reconnect time) in the following sequence:

  • after 7 seconds I hear all 3 Multipluses contactors actuating
  • after 15 seconds Victron increases AC out frequency at 53 Hz - HERE Fronius disconnects
  • after 30 seconds Victron connects on grid - again contactors actuating
  • Fronius monitors the grid for 30 sec (set grid monitoring time) then connects back after 30 sec (set grid reconnect time)

Is this the normal behaviour of the ESS system ?

2

Hey, I think that’s normal. I have the same setup, (also with fronius) and it does the exact same thing. I guess the 53 Hz increase is interntional so they make sure that every AC inverter is off while reconnecting to the grid.
I can only speculate why, here my guesses:

  1. The AC Sinus can be shiftet a bit after reconnect so the Inverter would stop anyway → but unintentional (not so “clean”)
  2. The System has to be sure there is the same voltage between off and on grid while connecting, so it sends an “off” Signal to all inverters and consumer. So this could help to prevent voltage fluctuations while reconnecting.

Maybe someone (from victron) knows more? :slight_smile: