Node-RED logic to disconnect AC-in based on unstable grid frequency

Node-RED
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1

Hi all,
I’d like to start a discussion for controlling AC-in connection/disconnection based primarily on grid frequency stability, not just voltage.

Background / why

We recently installed our first grid-tied Multi RS system (we previously did grid-tied installs mostly with MultiPlus / Quattro; Multi RS has been used by us mainly off-grid until now).

This site is on Easter Island (Rapa Nui) where the grid is notoriously unstable. For the first ~10 days the Multi RS tracked the grid fine, but then we experienced ~2 days where the AC-in relay was clicking constantly (rapid connect/disconnect). After inspection we correlated it with grid frequency going “roller-coaster” in VRM.

What I’m trying to achieve

I’m looking for a Node-RED algorithm on the GX device that evaluates grid stability and decides whether the inverter/charger should:

  • stay grid-connected (normal operation), or

  • temporarily switch to Inverter-only / AC-in disconnected when the grid frequency becomes unstable,

  • then reconnect once frequency is stable again (with proper hysteresis / delays to avoid relay chatter).

This is for a guest house: sometimes loads are tiny (no guests), sometimes loads spike (kettle / AC / etc.). So it cannot be permanently off-grid — it must reconnect to grid in “emergency” scenarios or when battery/solar cannot support the loads.

Existing logic (voltage-based, simple)

On other sites with chronic low voltage I already use a simple Node-RED rule:

  • If PV + battery can cover loads → run inverter only (don’t “copy” bad grid voltage)

  • If battery is low → connect to grid just long enough to recover, then isolate again

Now I want the same idea, but triggered by frequency instability (pattern/noise/rapid deviation), not merely undervoltage.

Questions for the community

  1. Has anyone already implemented a frequency-stability detector in Node-RED (GX) that drives AC-in connect/disconnect?

  2. What’s the best signal / DBus path you use for AC-in frequency (and/or “grid is OK” flags)?

  3. Recommended approach for debounce / hysteresis / minimum time connected/disconnected to protect the relay and avoid oscillations?

What I’m thinking (rough requirements)

  • Use AC-in frequency as input

  • Detect instability via one of:

    • frequency outside thresholds for X seconds

    • high rate-of-change (Δf/Δt) above threshold

    • standard deviation over a rolling window above threshold

  • Actions:

    • If unstable → force inverter-only (disconnect AC-in)

    • If stable for Y minutes → reconnect

    • Override: if SOC low / battery power limit reached / load too high → reconnect even if grid is marginal (best-effort)

If anyone has an existing flow or even just a proven strategy, I’d really appreciate it.

2

Happens even if you disable the “UPS function” in grid settings section?

3

Unfortunately, yes.

Here screenshot of the graphs during the affected period - first half is AC out Voltage, so the fat chunks are the times when the Inverter decides to Ignore AC Input and reverts to Inverter only so the AC Out spikes to 230V.

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