Fronius AC Coupled PV causing overcharging

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munga asked Aug 03 2023 at 12:57 PM

Fronius AC Coupled PV causing overcharging

I had a strange result today on a 2 x 5MP2 (10kVA) and 8.2kWp Fronius Primo with 9.99kWp (18 x 555Wp) panels. The system is connected to a Solar MD battery 14.3kWh.The problem was that the system continued to charge the battery even though it was at 100% causing the battery to charge to almost 58V. The BMS had parameters of CCL = 4A and CVL 52V yet it continued charging. Note this was not during a grid outage so not using FPSC to shift the power down.

Load demand on the inverter was about 200 - 300W.

The AC coupled Fronius is setup as ESS and per the Victron Guide. 1 : 1 (10kVA ( 5 + 5) : 8.2kW). Is it a problem with battery size?

Modbus TCP power limit control

Battery Voltage and Current

CCL, CVL and DCL

Multiplus-II AC PV Coupling Fronius

9

Alexandra ♦ commented · Aug 03 2023 at 1:10 PM

@munga

We need a bit more data here.

What is the frequency at this time?

Does the Fronius have the throttled state?

How are the comms set up?

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munga Alexandra ♦ commented · Aug 03 2023 at 1:15 PM

So as I said the FPSC was not active as the grid was present. The Cerbo and Fronius are all hirdwired to a network switch so using Modbus TCP to control the power. I posted a graph of the Fronius throttling as per special widget.

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munga Alexandra ♦ commented · Aug 10 2023 at 9:44 AM

Hi

So the issue arises when the grid is present, not while doing FSPC. The Fronius is running throttled, you can see the time lapse of the power limiting but it seems this is not limiting enough allowing the battery to overcharge.

Here you can see the BMS cutout when the voltage got too high.

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throttling.png (28.5 KiB)

bms-cutout.png (36.9 KiB)

spatula commented · Aug 14 2023 at 1:25 PM

Hi Munga, were you able to resolve this?

I have the same problem with 2 x 5MP2 (10kVA) and 3.6kWp Fronius Primo with 12.1kWp (22 x 555Wp) panels connected to a Solar MD battery 14.3kW. No need for me to post my charts, they are like yours.

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munga spatula commented · Aug 15 2023 at 7:53 AM

I'd be interested if you get a solution to this. I see Fronius have released FW version 34310 for the Primo. I'm going to try to update to that.

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munga spatula commented · Aug 15 2023 at 2:23 PM

How do you have 22 x 555W on a 3.6kWp Primo?

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Alexandra ♦ munga commented · Aug 18 2023 at 3:53 PM

Also not following the 1:1 rule there so not surprised.

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munga Alexandra ♦ commented · Sep 05 2023 at 7:58 PM

The 1:1 rule is for offgrid, these issues occurred on grid. The issue is a faulty MP2 pair on the same phase:

https://community.victronenergy.com/questions/229608/charge-current-offset-with-parallel-multiplus-ii.html

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munga spatula commented · Sep 05 2023 at 7:57 PM

Yes:

https://community.victronenergy.com/questions/229608/charge-current-offset-with-parallel-multiplus-ii.html

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munga answered · Sep 05 2023 at 7:56 PM

I answered my own question

https://community.victronenergy.com/questions/229608/charge-current-offset-with-parallel-multiplus-ii.html

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Answer 1 · 2023-08-10T09:48:39Z

munga answered · Aug 10 2023 at 9:48 AM

You can see AC consumption is well below the limit of the throttling causing the battery to overcharge.

ac-consumption-vs-pv-limit-vs-battery-voltage.png (86.0 KiB)

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Alexandra ♦ commented · Aug 14 2023 at 2:50 PM

@munga @Spatula

The system is requesting is not requesting the charge. The Fronius most likely is not responding or possibly not receiving the signal to throttle. This points to the Fronius not set up correctly.

How is the Fronius programmed? did you go through all the steps in the DNO editor?

That is pretty massive sudden voltage rise with not many amps. Maybe lower the charged voltages a bit on the battery as well. or cap it in DVCC. lower the grid charge amps and let the battery charge up slower. On a side note, I have seen a few cell failures in Solar MD batteries, are the cells ok? balancing ok and all that?

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1692024928630.png (42.9 KiB)

munga Alexandra ♦ commented · Aug 15 2023 at 7:39 AM

It feels as if the response from the Fronius is not fast enough. The comms and settings are correct as far as I can tell. These are the actual settings:

Modbus settings

DNO settings - controlling via Modbus and then via DPR as fall back in case comms is lost.

The Cerbo GX and Fronius are hardwired via a dedicated 5 port Ethernet switch.

Fronius is setup and talking to Cerbo GX:

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tcp-modbus.png (51.0 KiB)

munga Alexandra ♦ commented · Aug 15 2023 at 7:43 AM

Cell voltages are within 0.03V over 48 hours - no cells seem bad

No alarms etc.

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2-day-cell-voltages.png (28.7 KiB)

cell-alarms.png (18.3 KiB)

munga Alexandra ♦ commented · Aug 15 2023 at 7:49 AM

Fronius is definitely getting signals to throttle. You can see 48 hours of throttling. I am not sure how the Victron decides what to tell the Fronius to throttle by but it seems that the Victron is not getting the throttling correct. When the battery is full the throttling should be lower than the household demand and it is constantly higher hence over charging is happening.

I have many sites (15+) with AC coupled PV but this is the only site that has this problem. Main difference is they are single MP2 with Fronius 5kW. I am not sure how the system decides what to throttle by.

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fronius-running-throttled-3.png (28.6 KiB)

Answer 2 · 2023-08-14T15:23:06Z

spatula answered · Aug 14 2023 at 3:23 PM

Hi Alexandra,

Thank you.

The installer will be fitting a Solar MD logger tomorrow to collect as much info as possible. I'll let you know what we find. Regarding the configuration the installer has done some thorough checking and I'll pass on your comments to them.

Answer 3 · 2023-08-16T14:00:16Z

munga answered · Aug 16 2023 at 2:00 PM

My suspicion is that this overcharging is related to dual (parallel) multiplus-II install. It is almost as if the 2 inverters are both demanding power from the PV therefore doubling the required amount and hence overcharging this battery. Instead they should be each halving the demanded power.

Answer 4 · 2023-08-18T08:53:20Z

munga answered · Aug 18 2023 at 8:53 AM

Anyone got some insight into this?

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Alexandra ♦ commented · Aug 18 2023 at 7:39 PM

@munga

What are the battery charge settings on the Victron?

58v is way high and Solar Md charges only to 54.6v, I do in practice run them a little lower than that.

Have you tried cappjng the voltage in DVCC to 54v?

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munga Alexandra ♦ commented · Aug 20 2023 at 12:51 PM

Yes I tried to cap it at 55v under DVCC but it just overcharges. System running under BMS control but Victron overrides these and keeps charging.

All the settings are as per the guide for Solar MD:
https://www.victronenergy.com/live/battery_compatibility:solar_md

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Alexandra ♦ munga commented · Aug 20 2023 at 1:14 PM

@munga

Confirm under services in the GX modbus tcp is enabled?

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Fronius AC Coupled PV causing overcharging

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