MultiPlus-II ESS shows very slow and constant power ramp after grid reconnect

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1

I am running a mobile ESS system based on multiple Victron MultiPlus-II inverters with battery storage. The whole system is controlled by an external software (LabVIEW).

Through a communication table (register IDs), I send the following parameters to each inverter:

  • Active power setpoint per unit (e.g. -5000 W per inverter for discharge)

  • Permission to charge / discharge

The system is used for different testing and validation purposes.

System setup:

  • 3-phase connection to building grid via CEE 32 A supply

  • External switch logic with contactors

  • All inverters switch on after ~60 seconds in a coordinated sequence

  • Initial state is pass-through mode (grid is directly passed through)

Control sequence:

  1. System starts in pass-through mode

  2. Power setpoints are written (e.g. -5000 W per inverter)

  3. A signal enables “discharge allowed”

  4. Expected behaviour: all inverters ramp up to the requested power within seconds

Observed behaviour:

First start (after grid connection):

  • System works as expected

  • Power setpoints are reached within a few seconds

  • Fast and stable response

After grid disconnection and restart:

  • Power setpoints are only reached very slowly

  • Ramp rate is very low (around ~3 A per minute equivalent)

  • In some cases, target power is barely reached or takes a very long time

When this slow ramping happens, the increase is completely constant over time.
It is not stepping or oscillating, but a steady linear ramp until the target value is reached.
It then takes several minutes to reach the requested power setpoint: e.g. 7 minutes for reching 5 kW

Question:

What could cause this very different behaviour between first start and restart after grid loss?

Specifically I would like to understand:

  • Does the MultiPlus/ESS system have an internal state after grid loss that limits ramp speed?

  • Are there protection or synchronization mechanisms (grid reconnect, DC bus stability, etc.) that reduce power ramp rate?

  • Are there known conditions where power ramping is strongly limited (SOC, grid code, frequency/voltage stability, ESS state)?

  • Could this also be related to how external control via registers is applied (timing or state transitions)?

Can anyone explain this behaviour and suggest how to fix it?

2

Best thing to do is to check the behaviour is the same without your control software and any other modifications.

If it persists then it is the usual ramp behaviour on reconnect, something that is affected by the grid code as well.

3

Regular ramp rate in ESS is 400W/s.

Which gridcode have you set, maybe it contains a slower ramp rate after a loss-of-mains with the intention to only slowly load the mains after a failure. First startup of the MP could be considered normal, second is then slow LOM ramp

4

The standard ramp rate doesn’t apply to grid acceptance after loss of mains.

5

Thats what i meant, sorry. On first start/connect the MPs use the standard rate, on the second they use the one defined in the gridcode, if there is one

6

Here are 3 different grid codes, they all specify reconnection times.

G99: greater than 20 seconds
South africa: Greater than 60 seconds.
Europe (note the detail);

Screenshot 2026-04-13 at 15.56.09
Screenshot 2026-04-13 at 15.56.09734×424 83.5 KB

7

But reconnect time is not the ramp rate. In the picture theres normal reconnect at 0s for 100% (so i assume the standard 400W/s applies) and at the bottom is after LOM, 600s for 100% which could be what @H-Asmer sees.

So you could set that to 0s as well since its solely a test unit

8

Yes, the 10 minutes to 100% restriction is the cause. All codes have something to this effect.
In my region it seems to be around a minute, but then I don’t usually use large amounts of power, so it may be longer.
If regulations permit then the best option is to modify or use another code and see if that helps.