Grid export occurring despite PreventFeedback=1 and MaxFeedInPower=0 — 3-phase MultiPlus-II system

Q&A and troubleshooting
, , , , , ,
1

Hello,

I have a 3-phase ESS system and I’m experiencing
unwanted grid export despite having all zero-export
protections enabled. The grid meter (utility company
meter) registered a peak export of 72W.

System configuration:

  • 3x MultiPlus-II 48/6500/100-50 (3-phase)
  • Cerbo GX MK2, Venus OS 3.73 (latest firmware)
  • JK BMS connected via CAN bus
  • VM-3P75CT energy meter (installed on grid input,
    before MultiPlus AC-in)
  • SmartShunt 1000A
  • 16S LiFePO4 battery, 16kWh / 330Ah

ESS Settings:

  • Mode: Optimized without BatteryLife
  • Grid metering: External meter
  • Multiphase regulation: Individual phase
  • Minimum SOC: 10%
  • Grid setpoint: 150W

Zero-export protections enabled:

  • AC-coupled PV feed-in: OFF
  • DC-coupled PV feed-in: OFF
  • Limit system feed-in: ON
  • Maximum feed-in: 0W
  • PreventFeedback = 1 (set via MQTT:
    W/{VRM_ID}/settings/0/Settings/CGwacs/PreventFeedback)
  • MaxFeedInPower = 0 (set via MQTT:
    W/{VRM_ID}/settings/0/Settings/CGwacs/MaxFeedInPower)

Both MQTT values confirmed via readback as correct.

What happened:

  1. System was running normally with AC-in connected
  2. Turned on a 3kW electric heater
  3. System drew from battery (DCL limited to 30A)
    and topped up from grid
  4. Turned off the heater
  5. VRM showed grid L1: -1044W (export!)
    while L2: +112W and L3: +105W
  6. Total grid showed -799W
  7. This continued for approximately 30 seconds
  8. I manually disconnected AC-in
  9. Utility meter confirmed peak export of 72W

Note: No PV is installed in this system.
The export was from the battery, not PV.

Questions:

  1. Why did PreventFeedback=1 not prevent
    battery-to-grid export?
  2. Does PreventFeedback only prevent PV feed-in
    and NOT battery feed-in?
  3. Is there a known issue with PreventFeedback
    in Venus OS 3.73 on 3-phase systems?
  4. What is the correct way to achieve absolute
    zero export (including battery) in a 3-phase
    ESS system?

Thank you

2

Power variations of your PV and consumers makes this goal almost impossible, mainly because system cannot instantly react to all variations.

The only way, known to me, is to go higher with Grid Setpoint, with the expense of higher consumption from grid.

3

Which grid code are you using? The standard power ramp in grid parallel is 400W/s, but the grid code could alter that, further reducing the ramp rate.

With your 3kW load switching i would expect the system to regulate to zero feed in/out in theoretically 7.5s, but realistically id go for 10s. In that time, import/export happens. Apart from physically disconnecting from the grid theres nothing you can do to avoid that.

Has nothing to do with this situation, but your battery is somewhat undersized for 18kW of inverter power. Id reconsider that.

4

Hey,
Thanks for answer, grid code is: EN50549-1:2019, any sugestions for grid code change?

And I know battery is undersizded but im building the whole ecosystem, and there is limit of discharge set.
Thanks :wink:

####update ####
“Problem” fixed, issue was with indeed grid seetings i was not waiting for 600s after connecting the grid:

image
image498×139 57.3 KB

After 600s waiting eveything is working smooth :slight_smile:

5

I was going in the same direction.

AFAIK, EN50549-1:2019 does not define a ramp rate for regular use, only for special situation like reconnecting after grid failure, over/under voltage or over/under frequency events. For normal regulations it only defines that the ramp rate needs to be configurable by the DNO, but not an exact number.

If you look into the grid code settings, you can see the normal connect ramp rate, which is set at 100% in 0s, so in other words the 400W/s Victron standard rate applies. For your 18kW system, 45s for 100% would be the same as 400W/s. Further increasing the time only reduces the ramp rate.

image
image437×424 5.97 KB