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plaaspondok avatar image

"AC Coupled PV - feed-in excess" set to "OFF", does not change AC Out frequency for PV inverter when on-grid.

"AC Coupled PV - feed-in excess" set to "OFF", does not change AC Out frequency for PV inverter when on-grid.

I have a PV inverter coupled on AC OUT 1, and the AC frequency shift works well when not connected to the grid.

But when connected to grid, the AC OUT frequency does not function as expected to throttle down the PV inverter to prevent feed-in excess to grid - it incorrectly keeps the AC OUT frequency unchanged at 50Hz and the excess PV power is (unwanted) fed back into the grid, even with "AC Coupled PV - feed-in excess" set to "OFF" in the ESS setup in the Cerbo GX. I also tried "AC Coupled PV - feed-in excess" set to "ON" with "Limit system feed-in" to "ON", but with "Maximum feed-in" set to "0W" - but excess PV power still get fed back into the grid since AC OUT frequency does not change to throttle down the PV Inverter, when connected to grid.

(Again, when not connected to grid, frequency control works perfect. Only when connected to grid, I cannot get the system to NOT feed in excess PV into grid.)

It is like "AC Coupled PV - feed-in excess" set to "OFF" is not respected at all.

Any ideas out there perhaps? Or what am I missing here?

gx deviceModbus TCP
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4 Answers
Alexandra avatar image
Alexandra answered ·

@PlaasPondok

Is your pv inverters one of the compatible ones?

When connected to the grid, the victron itself does not frequency shift as it is syncronises with the grid. The pv will be controlled through the GX device to prevent feed in.

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shaneyake avatar image
shaneyake answered ·

The inverter can not change frequency when connected to grid because that would require shifting the grid frequency which it can not do.


You have to have some other way of communicating to the PV inverter to throttle down. If your PV inverter has no coms to victron system then you will probably need to install meter from that PV manufacture to prevent feedback.

Right now zero-feed-in is only supported by Fronius inverters but can be made to work with other inverters.

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plaaspondok avatar image
plaaspondok answered ·

@Alexandra @Daniël Boekel (Victron Energy Staff) @shaneyake
The PV inverter concerned is SMA Sunny Boy. Will SMA power control be technically possible via Modbus TCP at all? If so, is there any plans for Victron to support Zero Feed-in for SMA as well, similar to that of Fronius perhaps? If not officially supported by Victron, is it possible to write code for Cerbo GX or Assistance to custom build such functionallity perhaps?

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Do you know if your Sunny Boy supports Modbus? If yes, then you should be able to control it from your GX using some custom code or NodeRed.

@shaneyake Yes, SMA Sunny Boy does support Modbus. Where do I start searching on how to custom code in the GX or NodeRed? Any pointers will be greatly appreciated - I am a novice at this. Thanks!

Running NodeRed on the Cerbo
https://www.victronenergy.com/live/venus-os:large

You can then install a Modbus TCP pallet and use that to send commands to the SMA.

Do you have the modbus register addresses for the inverter?

plaaspondok avatar image
plaaspondok answered ·

@Alexandra @Daniël Boekel (Victron Energy Staff) @shaneyake
So just a bit of feedback - With Node-RED and Modbus on the Cerbo GX running Venus OS Large, I have managed to dynamically set the active power of the SMA Sunny Boy to follow the curve of the AC Load every 5 seconds, when SoC > 98%, which then reduce AC Inverter power even to zero, if and when needed. Problem Solved!

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Very interesting, do you mind sharing the details so that others can replicate this?

@Phil Gavin@Alexandra@shaneyake

Hi Phil. If you are familiar already with Victron OS Large, Node-RED, Modbus registers for your device, then this is the basic script in principle you can import as JSON into your Node-RED editor, attached: SMA Sunny Boy AC Power Control from Victron GX OS.txt

With a bit of Javascript you can build a lot more of inteligence and automation into the mix.

The webpage containing SMA Modbus address registers:
https://www.sma.de/suchergebnisse.html?q=Modbus+Interface&L=0&id=24288

The current SMA Modbus address registers:
https://files.sma.de/downloads/SMA_Modbus-de-en_V25.zip