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DVCC for better battery management

Hi,

Offgrid MP + AC coupled SMA Sunny Boy (SB) with lead carbon super capacitor batteries. An additional BlueSolar MPPT controller is planned for the future but currently not connected.

I'm looking for more information about DVCC as I see unexpected/undesired behaviour, where the MP is telling the SB to reduce power generation (possibly to the point where the SB reduces power output to 0W) and subsequently starts to use the batteries to provide power to the loads. After a little while, the SB ramps up power generation again (presumably in response to a lower frequency generated by the MP) and provides power to the loads and the MP starts charging the batteries again. This seems to particularly happen once the batteries are full.

While this might well be normal when an addiotional load just comes on (and the SB was more or less idling due to full batteries); I would not expect it to happen during the time that a larger load is present. Note there's normally an AC base load of at least 100W.

Does it make sense to enable DVCC in VenusOS for this AC coupled system? Where can I read about how this works in more detail? I did look at the Victron manual page and also searched the internet but so far haven't found much that is relevant.

Jan


DVCC
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3 Answers
John Rushworth avatar image
John Rushworth answered ·
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jbakuwel avatar image
jbakuwel answered ·

Good morning Matthijs,

I did read the information in the CCGX manual but was hoping to find something more detailed. For example I am unable to ascertain whether enabling DVCC potentially improves what I see happening here (in an off grid non ESS system).

I am not sure if I'm asking why the PV inverter is derated early :-)

I understand this paragraph: "To prevent DC and AC voltage overshoots because of varying solar irradiance and/or load fluctuations, it will limit the charge current already before battery voltage has rised up to the absorption voltage. It will derate the maximum charge current from 100% at 13.5 / 27 / 54V to 10% at 14.4 / 28.8 / 57.6V. These thresholds are not related to the configured absorption voltage." with regard to "early derating".

What I do not understand is why these thresholds are not related to configured absorption voltage: after all this is different for different battery types. For example, these voltages for the LCSC (lead carbon super capacitor) batteries I have here are (at 25 deg/C): absorption 55.20V and float 53.88V.

I see the following sequence of events:

- batteries full & small AC base load of 100-200W
- PV inverter is derated and providing power to AC loads and a small current into the batteries
- (so far so good)
- larger load (1-2KW) comes on
- PV inverter ramps up power after a little while [good]
- PV inverter is derated while larger load is still present to the point where the PV inverter display reads 0W (both physical display and on VenusOS) [not so good]
- PV inverter ramps up again while larger load is still present
- sometimes this repeats

I also need to learn more about what the MP does. I see the MP going back to absorption charging when the batteries are full after a momentary voltage drop caused by a large(r) load (say 2KW) for a few minutes where the load is briefly/initially supplied by the MP but once the PV inverter ramps up that load is supplied by the AC coupled PV inverter.

Please note I'm not asking for help with the events above: I can only do that after I've analysed it in more detail. It could also be something related to the Sunny Boy; at this stage I'm only assuming the SB is simply following orders from the MP.

But I'd like to learn more about the DVCC function in VenusOS so I understand what it is doing.

regards,
Jan



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mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

hi, DVCC documentation is here:

https://www.victronenergy.com/live/ccgx:start


Let me know if you miss anything.


You are asking why, in an AC-Coupled system, the PV inverter might derate early, right? See here:

https://www.victronenergy.com/live/assistants:pv-inverter-support


In particular chapter 3. Does that explain it?

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