High frequency issue when grid fails

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mmh asked Jun 24, '22

High frequency issue when grid fails

I work in a hospital in Mulanje (Malawi). We have recently connected 6 Quattro (6x15kW) with 6 Fronius Symo (6x15kW) AC-coupled. We have 6 battery banks (29 batteries in total). Each bank has a BMV and battery capacity of 500Ah (5x100Ah). 1 bank is different with 400Ah (4x100Ah). It is in Malawi not allowed to feed back to the grid. The system is running pretty good but we are dealing with one issue.

When we have low voltage (<180v) the Victron will switch from grid to the battery. Then the frequency goes up briefly to 52,9Hz or 53,1Hz. The next thing is that the Fronius-inverters shut down because of high frequency (error state 105). We have the correct county-settings in the Fronius (MG50). I know that it happens when there is no place to store the energy. But it happens also when the battery is at 40% and the hospital load is 40-60kW. The Fronius-inverters try to start up again and again but gives error until the grid-voltage is good enough for the Victron to go back to the grid. Normally it happens, between 11-2, when the sun is very strong and we need the Fronius-inverters to charge the batteries for the night. In the ESS is the possibility to change the frequency range but the advice to leave it like it is. I added some pictures for clarification. What can we do to solve this issue?

Thanks in advance, Gerwin Habermehl

ESS Fronius frequency

cerbo-briefly-high-frequency.jpg (2.6 MiB)

ess-settings.jpg (562.1 KiB)

frequency-settings-fronius-symo.jpg (2.4 MiB)

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Alexandra ♦ commented · Jun 25, 2022 at 12:32 PM

@MMH

Do you have a grid meter installed?

What is set to monitor the SOC in the system?

Do the fronius units still remain connected on grid falure?

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mmh Alexandra ♦ commented · Jun 25, 2022 at 04:41 PM

@Alexandra

Yes we have a grid meter (Carlo gavazzi). The SOC is monitored by Victron BMV's who communicate with a cerbo GX. The settings are now that we use the batteries by night until 40% and charge during the day if possible with solar. The Fronius inverters do continue by grid failure. Actually by normal grid failure the continue very good. Only when one of the phases has low voltage and the Victrons switched to batteries the Fronius inverters shut down due high frequency.

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marekp commented · Jun 25, 2022 at 07:03 PM

@MMH

Since you have Quatro units, how is the anty-islanding done in your system?

Is single input relay allowed in your country?

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Modifications Space

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Answer 1 · 2022-06-25T13:16:02Z

marekp answered · Jun 25, 2022 at 01:16 PM

@MMH

I had a similar problem when only one phase was missing (I think it was L3).

https://community.victronenergy.com/questions/129044/3-phase-system-and-1-phase-missing-what-should-hap.html

System switched to inverting.

Battery was not full (57%) but Fronius was frequency shifted off.

The only solution was to disconnect the system from grid on all 3 phases.

When I did that Fronius came back to life.

Later on, Victron Service confirmed that this is expected behavior.

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mmh commented · Jun 25, 2022 at 05:04 PM

@MarekP

That is indeed de same issue. We are now changing some battery voltage settings to see if that makes any difference. I will let you know when it helps. So you are still switch manual when you deal with this voltage issue? Or can you maybe program a relay switch?

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marekp mmh commented · Jun 25, 2022 at 06:57 PM

@MMH

Before you start looking for solution please read the answer I got from Victron Service regarding that problem.

In the last sentence they suggest the solution that works.

"That frequency shifting issue is how it has always worked. Yes it could be better and it will be looked at in the feature.
As long as some AC input is present, the units keep "getting ready" to connect as soon as voltage is within limits.
This means that to prevent overvoltage on the output, the PV inverters are shut down by periodically raising frequency.
We hope to change this in de feature, but if that happens it won't be soon.
To overcome the issue, in locations with a lot of grid disturbance sometimes a grid safety relay is used."

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mmh marekp commented · Jun 27, 2022 at 09:59 AM

Thanks for sharing

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Answer 2 · 2022-07-24T11:04:13Z

Hi all, help appreciated again for this system running in a rural african hospital;

Following up on above, the issue seems to be more complicated then low voltage on one grid phase.

I checked the VE.Bus monitor when:

A. state 105 error appears on fronius and B. At the same time Quattro's refuse to connect AC-input 1 (grid in our case, genset sits on AC-input 2).

VE.Bus monitor in this case shows that AC1 voltage is perfectly normal 220V on 3 phases with normal frequency-in of 50.1 Hz. So we can't blame the utility company.

Frequency-out is 52.9 Hz - I suspect due to upregulation by the Quattro to reduce PV power.

Result: no PV (Fronius downregulated through frequency shifting) and no AC-1 (grid) input as frequency in and out do not match! this unhelpful situation exists for many hours every day mostly during sunny hours.

My only solution until now is to close main grid switch and make this an off-grid system, then everything works well.

All modbus settings in Fronius datamanager are correct, grid-feed in is not allowed on GX device settings (ESS) and works well.

System has 6x15Kw fronius symo on AC-output and 2x15Kw symo on AC-input.

6x Quattro 15kW, all properly sized cabling done by professionals.

1x Fronius and 1x Carlo Gavazzi grid meter and Cerbo as GX device.

Other details above.

I tried:

- allow grid feed-in with limit of 5000W, this made no difference

Considering now:

- Delete ESS assistent and use the ignore AC1-input virtual switch. However shame to lose all good ESS features, also not sure if this would help.

Any ideas?

A second problem is that our new 65kVA diesel genset is accepted on AC2-in, without the GX device (cerbo) connected. The moment I plug in the Cerbo, it disconnects. Suspecting again that the ESS assistent does this as there seems to be no physical issue with the genset.

Here I tried all options for genset issues as per documentation (weak AC input checked, UPS unchecked, accept wide frequency checked) but not yet 'disable LOM on AC-input 2.'

Comments on these two issues would be much appreciated. Thanks

Answer 3 · 2023-12-11T12:42:37Z

assyntdavid answered · Dec 11, 2023 at 12:42 PM

@MMH Regarding the frequency shifting issue shutting down the PV inverter, have you come across this post https://community.victronenergy.com/questions/8792/multiplus-485000-with-pv-installed-45kw-output-hz.html

I found your post because I have a similar problem with a simpler system using a Multiplus 2 (ie only one ACinput). This morning I found his solution of reording the Assistants, ie move general flag to position 1 and ESS down to position 2. It has worked for me!

All the best,

David

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Answer 4 · 2023-12-11T12:51:11Z

mmh answered · Dec 11, 2023 at 12:51 PM

Hi @assyntdavid assyntdavid

Thanks very much for your input, much appreciated. The issue was resolved for us by upgrading our connection to the transformer. We went from 3x16mm2 to 3x100m2 aluminum over a distance of 300m, renewed the fuses at the transformer and upgraded the connection to it. This solved the issue - so it was the poor quality grid connection is what caused it. We only run the ESS assistant, no others.

Since we very often have undervoltage in Malawi we also installed a contactor +voltage window regulator before the system around the same time. This effectively results in a grid-lost situation when there is undervoltage so that the PV inverters happily work for us on the micro-grid. All in all it took a lot of money and time but we're happy how it works now for our hospital.

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