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Nazareth Kevorkian avatar image
Nazareth Kevorkian asked

AC Coupled Fronius Drops Power on Shifted Frequency Prematurely and More than Needed

Hi, I have an AC-coupled Fronius Symos on 3-phase configured Quattro inverters. I have enabled Frequency shifting in ESS assistant with pre-set configuration: starts at 51, lowest at 52.7, shuts down on 53Hz. I have set the Fronius on MG50 to enable this power reduction on shifted frequency. But lately I noticed that at 80% SOC, the frequency starts shifting up, and the batteries cannot be charged properly on AC PV power, although enough power to charge them fully is available. I also know that Fronius on MG50 starts power decrease at 51Hz and shuts down on 52Hz. What can I do to have better charging for my batteries on AC PV (start frequency shifting on 90% SOC and end with 53Hz on 100% SOC)?

ESSFroniusAC PV Couplingfrequency
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Hi,

what battery do you have? CANbus managed Lithium?

BR

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Rolls 2YS31P. I have a BMV700 as a monitor for the batteries.
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2 Answers
shaneyake avatar image
shaneyake answered ·

I would change the settings to the settings victron recommends and see if that fixes it.
https://www.victronenergy.com/live/ac_coupling:fronius

50.2 Start
52.7 Minimum
53.0 Disconnect

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Hi @shaneyake thanks for the reply. Actually I made mistake in the question. It was set just at the recommended settings: 50.2 start, 52.7 minimum, 53 disconnect. BUt it did not function properly and I have undercharged batteries always.

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Nazareth Kevorkian avatar image
Nazareth Kevorkian answered ·

Update:
I made these changes to the ESS assistant configuration to iterate on results:

Frequencies:

  • Start 50.2 > 50.1
  • Minimum 52.7 > 51.5
  • Disconnect 53.0 > 52.5

What I noticed last 2 days, is that at the Quattro shifts the frequency up to 52.5 at 80% SOC, which reduces the PV output but does not disconnect (Fronius disconnect is at 53Hz). This takeaway is important, because the ESS wants to disconnect the PV power completely to protect the batteries, when the batteries are still at ~80% SOC. This is exactly the scenario I wanted to avoid.

What are the criteria based on which the ESS shifts the frequency: is it the SOC, the Voltage, etc? I would like to be able to do full bulk and absorption up to 90-95% SOC in a pure off-grid Solar scenario and I somehow am not able to control the frequency shifting ESS conditions to enable that.

@Johannes Boonstra (Victron Energy Staff) could you please help me with this issue?

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On the GX under system settings, is the Battery monitor set to your BMV? Is the Battery Monitor in the Quattro turned off?

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On CCGX, the battery monitor is on Automatic and it has been always auto-selected on BMV700 on VE.Direct.

In VE.Config settings pushed into the Quattros, under General tab page, the battery monitor is selected. Shall I deselect it?

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I would set the Battery monitor to BMV700, auto doesn't always work.


From my understanding, if you are using a external Battery Monitor you should uncheck the VE.Config Battery monitor.

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Done. But do you believe that this is the problem? I believe that the problem is elsewhere, because w/o changing these settings with just ESS frequency settings change the behavior changed.
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If the Quattro isn't getting the correct battery information it will frequency shift incorrectly.

So in mind, what you are saying is that the system is reducing the charging too early makes me believe the system doesn't know the correct state of the battery is. Let's see what these settings do.

Is the ESS settings still?
50.2 Start
52.7 Minimum
53.0 Disconnect

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It is now.
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Is everything working now?
Can you post some screenshots of SOC and Frequency?

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Now we are at night and we happen to have grid AC in. We shall wait until tmrw day time.
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@shaneyake
Update: The Frequency shifting reaches 52.5Hz at 90% SOC and keeps the batteries on 90%. I would like to stabilize the batteries on almost 100%soc-freq-va.png

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soc-freq-va.png (137.1 KiB)
Okay, so we are getting somewhere.

Can you send me screenshot of the charger tab in VE.Config?
I am wondering if your float voltage is too low. It looks like it ran at 56v for 3 hours then dropped down to 50V. Is that correct?

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@shaneyake Here you go attached.

One thing to note, my battery bank is now comprised of 23 cells of 2V instead of 24. I am replacing one unit now. So please consider that in your calc, probably a good idea is to suggest a cell float voltage and then we can multiply by 23.

charger-tab.png

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charger-tab.png (81.0 KiB)

One other screenshot from today. Same behavior, shifting frequency to not charge more than 90% SOC.soc-freq-va-270821.png

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So from what I can tell the frequency shifting is working correctly. You might want to increase your Adsorption time to keep charging your batteries. You might also need to change the BMV reset point but it looks like everything is working according to the settings you have in the charger tab.

What type of batteries do you have? 2V lead acid?

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