ESS immediately shifts to 63 Hz and disconnects Huawei inverter when AC Input is present but rejecte

Q&A and troubleshooting
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1

Hello everyone,

I’m working on the following system:

  • 2 × Victron Quattro 48/5000 configured in split-phase
  • ESS enabled
  • Huawei SUN2000-5KTL-L1 AC-coupled on AC Output
  • Fidus lithium batteries with DVCC/BMS communication

I have observed what appears to be unexpected behavior and would like to understand if this is normal or if there is a configuration that can change it.

Scenario 1 – AC Input connected but rejected

  • Utility (AC Input) is physically connected.
  • The utility voltage is outside the accepted limits, so the Quattros reject the grid and continue powering the loads in inverter mode.
  • The battery is around 97% SOC.
  • The house load is approximately 4 kW.

In this condition, as soon as the Huawei attempts to synchronize, the Quattro immediately increases the output frequency to approximately 63 Hz, forcing the Huawei to disconnect.

It does not appear to gradually shift the frequency to regulate the Huawei’s output. Instead, it jumps directly to the disconnect frequency.

Scenario 2 – AC Input physically disconnected

If I open the AC Input breaker and completely isolate the utility from the Quattros:

  • The Quattros form the microgrid.
  • The Huawei synchronizes correctly.
  • The Huawei produces power normally.

Scenario 3 – Normal pass-through operation

When the utility voltage is within acceptable limits and the Quattros are operating in pass-through mode:

  • The Huawei synchronizes correctly.
  • The Huawei produces power normally.
  • Everything works exactly as expected.

My concern

The Huawei operates correctly in both of these situations:

  • Pass-through mode.
  • Islanded operation with AC Input physically disconnected.

The only situation where it is forced offline is when the AC Input is physically connected but rejected due to voltage being out of range.

Since the Quattros are already supplying the loads from the inverter and are not using the utility, I would expect the Huawei to synchronize with the microgrid created by the Quattros just as it does when AC Input is physically disconnected.

Instead, ESS immediately raises the frequency to approximately 63 Hz and disconnects the Huawei.

My questions are:

  • Is this expected ESS behavior?
  • Why does ESS immediately force a 63 Hz shutdown instead of allowing normal frequency-based power regulation?
  • Is there any ESS configuration that allows the Huawei to continue operating while AC Input is present but rejected?
  • Has anyone successfully operated a Huawei SUN2000 in this exact scenario?

Thank you for your help.

2

Are there any alarms or log information from the Huawei?
Is the Huawei grid detection causing the issue? eg is it backfeeding some power to the Quattro to check if grid mains power is alive?

Any history/log data from the Quattro that gives any insight?

Perhaps someone more familiar with the Huawei would have some thoughts.

3

The problem is it is still there and being ‘watched’ by the inverter.

You can influence this behaviour to some extent by adjusting the PV restart voltage.
While I haven’t worked with 60 Hz systems, on some 50 Hz installations setting the PV restart voltage to the float voltage (or adjusted off the defaults depending on the battery) has helped reduce the occurrence.

For reference, the reason newer inverters incorporate a double-disconnect arrangement is that the incoming supply can still be detected at the inverter terminals even when it is in a rejected state. To meet compliance requirements, a double-disconnect mechanism is therefore required (and why most of the newer models have it). This is why the Zeihl UFR1001E relay should be used, as this a ‘quirk’ of the inverter you have chosen not ess (or adjustable in ess) itself