ESS only reaches the grid setpoint when AC PV surplus feed-in is enabled

DIY
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1

Hello everyone,

I have a problem with the ESS control of my Victron system.

System:

  • MultiPlus-II GX 48/5000/70-50
  • single-phase MultiPlus on a three-phase grid connection
  • Fronius PV inverter currently on the AC-in/grid side
  • all loads currently also on the AC-in side
  • Shelly Pro 3EM as an external energy meter
  • connected via “Shelly 3EM HTTP JSON service”, firmware v0.1
  • ESS mode: Optimised without BatteryLife
  • Multi-phase regulation: Sum of all phases
  • Grid setpoint: 50 W
  • AC and DC PV surplus feed-in normally disabled

Symptoms:

As long as the battery is being charged and “AC-coupled PV – surplus feed-in” is disabled, the ESS does not reach the configured grid setpoint of 50 W.

Example:

  • Grid L1: 25 W import
  • Grid L2: 124 W import
  • Grid L3: 2 W import
  • Total grid: 152 W
  • PV power: 621 W
  • Battery charging: 409 W
  • AC consumption: 357 W
  • Battery SoC: 61%

It appears that the MultiPlus keeps its phase L1 only just in the positive range. The import on L2 and L3 is not offset by negative power on L1, even though “Sum of all phases” is selected.

As soon as I enable “AC-coupled PV – surplus feed-in”, the regulation works immediately:

  • Grid L1: approx. −96 W
  • Grid L2: approx. 145 W
  • Grid L3: approx. 3 W
  • Total grid: approx. 52 W

The MultiPlus then feeds in enough power on L1 to offset the simultaneous import on the other phases and reach the grid setpoint.

I also compared the Shelly measurement with the SML value from my official electricity meter:

  • Shelly/Victron: 52 W
  • official electricity meter via SML: 60 W

The individual phase values also largely match. I therefore consider an incorrect total value from the Shelly rather unlikely.

The problem when surplus feed-in is enabled:

When the battery is full, the available PV surplus is actually fed into the public grid. That is exactly what I want to prevent. When AC surplus feed-in is disabled, however, the Fronius is correctly throttled back when the battery is full, and grid import remains reliably at approximately 50 W.

My desired behaviour would be:

  1. While the battery is charging, regulate the sum of L1, L2 and L3 to 50 W.
  2. For this purpose, L1 may also briefly become negative, as long as the net total remains positive.
  3. When the battery is full, the Fronius should be limited and there should be no actual surplus feed-in.

According to the Victron documentation, a single-phase ESS with the “Sum of all phases” setting should actually compensate for the total value across all three phases.

Is this behaviour known? Is cross-phase compensation deliberately disabled when AC PV surplus feed-in is disabled, or am I still missing a setting?

Could the cause be the Shelly D-Bus service being used, even though the total and phase values are displayed correctly?

4

Does no one have any ideas about this? :blush: