David avatar image

Three Phase off grid and single phase generator

Hi Victron team,

An installer/customer of DPA Solar is designing a 3 phase off grid system (possibly 3 x Quattro 8kVa) and has asked me if a single phase generator can be connected to AC IN on the master? I've read through the tutorial on VE SystemConfigurator and see that a similar example (3 phase gen with single phase shore power) requires 4 Multis.

Do we need 4 Quattros if the customer wants to keep his single phase gen? Or do we tell him to purchase a 3 phase gen?



MultiPlus Quattro Inverter Chargerinstallation3 phase
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2 Answers
Johannes Boonstra (Victron Energy Staff) avatar image
Johannes Boonstra (Victron Energy Staff) answered ·

Hello David and Paul, The answer is as follows.

In principal a three phase system works as one unit.

So although in different boxes the state the units are in is equal.

This means all three phases need to be present ( with the correct rotation) before all units will go into passthrough ( and then start charging).

There is however a setting in VeBus system configurator that this behavior can be changed.

This is called switch as group, when this is disabled the units can " decide " themselves in which state they can be.

However there are some restrictions as the output frequency needs to be equal to the input freq as otherwise the unit start going out of phase.

So L1 is the leader in these systems where " switch as group " is OFF.

So if L1 gets a 230V source connected it will change the systems frequency to match the incoming AC voltage, so that the phase voltages stay the same.

Then the L1 can go into the passthrough state and charger mode (or even power assist) while the others remain in inverter mode.

In this mode you can also transfer energy through the dc side to the other phases of course. If in this case also L2 gets a AC voltage which is 120deg out of phase of the L1, this L2 can also go into pass through/charge. Same for L3. So in your case, when L1 gets the single phase genset and switch as group is OFF, this power will be used.

There are also restrictions!

When the PV inverter support Assistant (or ESS which has this function built in) is used the switch as group may NOT be used. The reason is that if there is too much power coming from the PV on AC out, the frequency cannot be changed as there is a single phase input on which the system is synced.

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Hi Johannes - We really appreciate this concise answer.

David W

Please assist:

So on a 3 phase system with the "Switch as a Group" being disabled in order to allow for a single phase Generator input,, you can not use the PV Inverter suppport, as it won't allow you to download the assistant. Is there no way using a single phase generator on the Master Multi when using PV Inverter support?

good day,

I am solving the same problem.
3ph quattro and 1 generator.
I understand the answer. However, in my case, the PV inverters will be on AC-IN, and charging will be controlled by ET340 meters. One will be at the input of the building, the other will be at the PV inverters.

So if the system is offgrid, the PV inverters will be disconnected (they are on AC-IN).
Is it possible to use ESS and "switch as group" together in this case?
The assistant will not change the frequency because there will be no inverters on AC-OUT.

Are my thoughts correct?

Thank you

Paul B avatar image
Paul B answered ·

I stand to be corrected here, as I have not done this, but my logic says that it should be posable.

However my understanding is

As each inverter is fully independant, but they all use the same battery bank and are each 120 deg out of phase from each other.

inother words set the system up as though it was going to have a 3 phase gen. but two phases would not be connected to any supply at all.

therefor you could connect a single phase gen to one inverter (best to be the master inverter),

I WOULD THINK and that one inverter would supply that say L1 phase plus the inverter charger would also charge the battery bank from that ONE inverter/charger only.

the other 2 inverters being L2 and L3 would draw off the battery bank, and supply the other two phases, so you would need to limit the consumption on those two phases to not be more than the battery chargers output on average. but then you may also have solar connected to gthe batteries and this would add to the battery charging.

Thats my thoughts, but I maybe totally wrong as well.

I dont think you would do any damage by trying , all that would happen is a shutdown I would think.

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Thanks but because I'm passing this back to a installer/customer, i need a definite answer, so I may have to wait for Guy or HQ. Have you done many 3 phase or parallel installs?