pauldeegan avatar image
pauldeegan asked

Ignore AC input when feeding back to generator OFF GRID

Hi, It would be good if we were able to program the multi to ignore AC input when current is detected feeding back to a generator (from excess of PV inverter). I have set up general user flag to ignore AC input, but there is no way of triggering it under these circumstances.

A bit disappointing.

Any suggestions?

ac coupling
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1 Answer
Alexandra avatar image
Alexandra answered ·


I am assuming that the GX has no control over the PV inverter. Does the PV inverter respond to frequency shift? If it does then run the generator at a frequency a bit higher to throttle it a bit.

If it is feeding back though it means it is covering loads and has extra to send to charging the battery so why is the generator running at this point?

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pauldeegan avatar image pauldeegan commented ·

Hi Alexandra,

I am well aware of the in and outs of the system. As an off grid designer, I think about how things can go wrong (Murphy's law). In this case it would be bad luck if this were to happen for many reasons, including the ones you have raised.

I would like a safety net. It is a software update that is sorely needed. If the Swiss cheese holes line up and there is excess PV that ends up being absorbed by the generator I think it would be good for the GX device to detect this (because it can) and then set "Ignore AC input" (it can also do this) for a predetermined time for the purposes of protecting the generator. Say ignore for 5 minutes and then try again. This will protect the generator.

When weak AC is on (this often needs to be set) the multiplus can only charge the batteries at about half power (e.g. 4000W for a 8000W multi). If you have 7kW of PV inverter coupled this means it is possible, under certain circumstances that power could backfeed the generator.

When selecting the grid code "Off Grid" it states in the grid code "feeding back to the grid not allowed".

I am aware of all of the things that can be done, assistants, contactors, AC out 2 relay for PV etc. I would like to see a software update for the multi to have in place its own safety net so that it will behave correctly, in line with the grid code, regardless of any setting or assistant that set.

Please please please Victron, make this update. @Guy Stewart (Victron Community Manager)

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Alexandra avatar image Alexandra ♦ pauldeegan commented ·
Didn't answer the question about if the PV inverter responds to frequency shifting there. If it did then the inverter would be able to throttle it when it needed to.

If you are off-grid then why do you need a grid code? Grid code then makes generator acceptance more difficult if it is not a well regulated one.

Maybe a bit more explanation is needed here.

It would be better to have the system shut the PV inverter down or throttle it rather than reject the generator.

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pauldeegan avatar image pauldeegan Alexandra ♦ commented ·
The PV inverter responds to frequency shift. When the generator is coupled it then has complete control of the frequency and this is the problem. Relying on the generator being tuned to give a slightly higher frequency and keeping the inverter output low is a poor design. It is no guarantee that it will not wander off in time.

I was merely making a point about the grid code. I am not using a grid code as it is off grid. Please disregard this.

I disagree that it would be better to have the system shut down the PV over the generator. If there is enough PV to provide the needed load then it would be better to have the system reject the generator input. Because frequency shift is the method to control the PV the MPII would then need to ignore the AC input so that it can then recommence frequency shift.

All that Victron has to do is add this feature to the next firmware. They have already added similar features such as generator warm up and cool down which are basically the same thing (ignore AC input under certain conditions and in doing so it is able to frequency shift during this ignore period)

I understand that what I am asking for is not in existence yet, but if I do not ask it will never happen. The current options for a solution are inadequate and unsuitable for my needs.

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