martin24 avatar image
martin24 asked

Parameters for AC-coupled PV-inverter connected to Multigrid

By now I have installed the BYD BBox 5.0 at a Multigrid (MG) and connected a Sunny Boy 2.5 (SB) with 2300Wp Modules.

If I try to use this as an island (mains disconnected) with only a 60W bulb as load and the battery nearly fully charged the following is happening:

Battery is working, MG is inverting and supplying the load, frequency is 50.01Hz.

After connecting the SB it will wait for some minutes, then starting and slowly increasing power up to e.g. 920W.eThe MG starts to charge the Battery. Frequency remains at 50.01Hz. Battery voltage is increasing as it it charged.
After some minutes battery voltage reaches 54.4V, MG starts to increase frequency. When 50.2Hz is reached the SB starts to reduce its power. Frequency is increased to 51.51Hz at which the SB still provides 460W (completely in line with AR4105).

Battery voltage is increasing to 55.6V. Then the MG switches off (or the BBox, I am not sure). After some seconds it starts inverting again, now at 52.01Hz. SB waits for 10 Minutes before starting up again. Freq. is still 52.01Hz, SB starts another waiting period. After some time MG reduces frequency to 50.01Hz, so SB starts again and the same thing is happening again.

I guess I need to adjust some values so that the MG switches off the SB by increasing frequency to above 51,5Hz before the battery voltage gets too high. Can you give me some advice which values to set?
Currently I have:
Bulk voltage 55.2V
Absorption: 55.0V
In ESS the frequency at which the AC couple PV interverter starts regulating is set to 50.2Hz, end of regulation 51.5Hz, Switch off at 51.51Hz.
Setting the last to 52Hz does not help.
If I set these values to 50.2/52.0/52.01 it now seems to be working.
But I would expect that the MG increases the frequency to at least the shut down frequency when the power generated is still too high and the battery voltage continues to increase. But for me it seems, the MG does not want to shut down the PV inverter even if it generates to much power for the battery to take.


MultiPlus Quattro Inverter Charger
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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi Martin,

From reading your question it sounds like you have the system working now, after modifying the settings to increase the frequency.

It could be that the default settings are not enough for your Sunnyboy.

Is this correct?

The multi only has control over the output of the solar inverter through frequency. If the multi is outputting 52hz and the solar inverter is still outputting power, then either a settings change on the solar inverters is required, OR an increase of the frequency on the multi OR a reduction in the charge voltage before the battery cuts off.

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martin24 avatar image
martin24 answered ·

Can you explain why there are separate settings for "end of regulation frequency" and "switch off" frequency?

I would expect that when setting regulation to 50.2 to 51.5Hz the multigrid will increase frequency to above 51.5Hz when at 51.5Hz there is still too much power from the PV-inverter.

But this does not happen, it will stick to exactly 51.5Hz and put the PV-inverters power into the battery which causes the battery voltage to get too high.

The SunnyBoy will not output any power at 52.0 Hz, but at 51.5Hz according to VDE AR 4105.

So my workaround (which seems to be working) is setting regulation in the multigrid to 50.2 to 52.0Hz. This way the multigrid "thinks" it can still reduce PV-inverter power by increasing frequency beyond 51.5Hz and the SunnyBoy gets the hint to switch off at 51.5Hz.

But I absolutely don't understand why regulation 50.2 to 51.5Hz, switch off at 52.0Hz does not work because the multigrid then never gets beyond 51.5Hz.

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ross-skyenergy avatar image ross-skyenergy commented ·

Hey Martin

I'm having a similar problem on off grid multi plus. AC coupled with a SB.5 set to MG50hz

I'm using the PV Inverter assistant and have it set to 51/51.5/52, I'm going to try your settings above if you see my below picture the multi doesn't seem to shift at 100% SOC, I think I need to play around with the bulk/absorption voltages as well.

Have you many improvements on yours?

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