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AC PV Coupling

AC and DC Coupled Grid-Tied System, PV Inverter throttled incorrectly

To all the experts or struggling enthusiasts like myself - I really hope someone can enlighten me as to why my system is suddenly behaving this way:

My setup:

  • 2x5kva MultiPlus II Inverters - 48v grid tied system
  • 4.5kW PV via a SolarEdge HD Wave 5kW PV Inverter - AC Output coupled
  • 6kW PV via a Victron 250/100 MPPT charge controller

Recently (which could relate it to a firmware update), my PV Inverter is getting throttled when my Critical Loads exceed a certain value (about 4kW). My battery is not full (83% in this case) and my PV Charger (MPPT) does not bring enough power to sustain my loads and charge my battery. This leads to my battery actually discharging while the sun is at max:


What is interesting is that when my critical loads decrease, to say 2kW, the PV Inverter kicks in again. This also happens when I add an AC Load (on the AC input side). Discussing this with a friend lead us to consider maybe the Factor 1.0 rule applies, but surely this should not apply as my PV on the AC Coupled side is only 4.5kW. But something makes me think that it has to do with either:

  • Prioritizing the DC coupled over the AC coupled (which does not make sense to me), or
  • It's trying to protect the system from an potential overload if the loads suddenly disappear

What is also interesting is that when the grid is off (this happens due to our lovely nationwide loadshedding) the PV inverter produces as expected and does not get throttled:


I'm running ESS assistant and feed-In is switched off (I'm not feeding back into the grid). There seems to be no frequency shifting happening in these cases (based on my VRM analysis, so I'm assuming the Multiplus or GX is communicating with my SolarEdge PV Inverter via modbus.

Can anyone please help me explain this phenomenon?

Previously @Izak (Victron Energy Staff) from Victron has been super helpful in diagnosing a comms issue between SolarEdge and the GX device, so I have all the faith in this community :)

wim-immelman asked
klausr commented ·

4 Answers

Multiplus frequency shifting: stuck at control range maximum


I use frequency shifting by a MultiPlus 48/3000/35-50 (firmware v430, off grid) to control electrical heaters via an AC Thor controller. The idea is to maximize PV power consumption. Layout:


My MultiPlus setup is the following (full settings attached):

Charger settings:

Absorption voltage 55.50 V (absorption voltage of set MPPT = 57.4 V)
Float voltage 55.10 V (MPPT float 55.2 V)

PV inverter support assistant settings:

*) The solar converter will start reducing its output power at 50.10 Hz.
Output power will be reduced to minimum when the frequency is 51.00 Hz.
The converter will disconnect when the frequency is higher than 53.00 Hz.
*) Total installed PV inverter power is 1500 Watts.
Total installed PV panel power is 1500 Watts.

The issue is that the MultiPlus frequently gets stuck at the maximal value of the frequency control range, i.e. 51 Hz. So not at the "disconnect" value of 53 Hz, which seems to be reset according to what is written in the documentation of the PV inverter assistant (at a voltage equal to Float V - 5.2 V).

An example of this issue is shown in the graph below. At time = 0 h (midnight), the system is already stuck at 51 Hz from the previous day (green curve), despite the fact that the battery voltage is 49 V or lower (blue curve), which is well below the charger absorption voltage setting of 55.5 V (dotted blue line). I had switched off the AC Thor loads the previous day, to avoid battery draining.

In the morning I remotely reset the MultiPlus to get the frequency back at 50 Hz.

At around 12:00 pm, the system did what it should: when the battery voltage increased above +/- 55.5 V (blue curve), the frequency shifted. I switched on the loads again, and AC power was sent to the heaters by the AC Thor controller (red curve). I have two sequential heaters of different power controlled by the AC Thor, explaining the variation in AC power consumption.

One can also see that at the end of the day, around t =18 h , the system again was stuck at 51 Hz (and so power consumption maximal at 1500 W), despite the fact that there was not enough PV power available and that the battery voltage reached values as low as 48 V. This is far below the absorption (and float) voltage set for the MultiPlus charger, so one would expect the frequency to be shifted back to 50 Hz. The battery was drained to 80 %, at which time the AC loads were switched off automatically by a Multiplus relay that I programmed for this purpose.

The problem is of course this behaviour drains the battery unnecessarily.

Weirdly enough, the issue does not always happen. Many times it just works as it should (see bottom graph). I did not find any regularity, except that it seems to happen on days with alternating sunshine/clouds, and after the Multiplus returned from the "disconnect" frequency, 53 Hz in my case. Similar behaviour has been reported a few times before on this forum (mostly in the context of frequency shifting for AC coupled PV charging) but a definitive solution was not given.

Can this be solved by changing the settings somehow? I tried many charger voltage/ frequency range settings already, but always the issue pops up. Or is this inherent to the way the frequency shifting is programmed?

Thank you.


Multiplus settings: MP_settings.txt

A good (sunny) day - example of how it should work:


alexander-aerts asked
Paul B edited ·

1 Answer

Experience connecting a Fronius Gen24 to AC-In of a Victron Quattro


Is anyone having the experience connecting a Fronius Gen24 Primo to the AC-In of a Victron Quattro? After activating the SolarAPI protocol on the Gen24, it is discoverable by the CerboGX and shown in the VRM. Still, instead of providing all the power to the load and the remaining one to charging batteries, the extra is injected in the grid. If I'm limiting the export on the Gen24 side, the inverter is reducing the power to match the needed power for the loads. I already wrote also to Fronius, waiting for their answer.


cristimv asked

0 Answers

Is AC Consumption a measured value?

My AC loads are supplied by the grid before Quattro. The critical loads on AC L1 are on the AC out of the Quattro, in addition to PV Inverter. Are my AC consumption values measured (how?) or are they calculated values?


shubham asked
shubham commented ·

1 Answer

Problem with AC current sensor 40 A

I have two PV systems. First is with MultiPlus 12/1600/70 and second one is MultiPlus II 48/5000/70 GX.

We have two different current sensors connect to the temp input of the both inverters.

Add AC current + ESS assistant. Upload to the each inverters. All last firmware. All requirements about main chip covered.

Restart Cerbo.

Wait 24 hours to calculate reactive currents and the values are not correct.

First I see that the measurement value is 350 W less than actual one. And the second the power of the PV inverter add to the AC load when is on input side or to AC critical loads when is on the output side.

I asked my local delaer - no answer. I ask in Romania - no answer.

Is anybody in this company to solve the problems?



May be there is a problem with web server who print the diagram to the browser.

Galin Radoslavov asked

0 Answers

Fronius throttled by Quattro despite being needed (AC/DC coupled system)

Hello all,

I have an AC/DC coupled system as seen below:


Half way through the day, the batteries got to 100% and I had a low load of around 1000W, which the DC coupled system handled while the AC coupled is throttled down to 0. Load eventually got higher than the capability of the DC coupled system, and yet the Fronius remains throttled.

BYD BMU raised the CCL a while ago and yet the Quattro didn't change its behavior:


And here's the Quattro throttling the Fronius:


I have two questions:

1. Obviously something is wrong here, Fronius should kick back in when CCL is above 0 to recharge the batteries

2. Why isn't the AC coupled prioritized when the batteries are full over the DC, given that would be more efficient for the AC load?

EDIT: toggling the dc switch of the Fronius didn’t help. Turned on my generator for few minutes then the Fronius started pulling power from its array. Turned off the generator and it is still going strong. A barbaric workaround though…

micmak asked
iwan answered ·

8 Answers

Multiplus II - PV Enphase microinverters on AC-out-2

MP2 48/5000/70 - GX

I have some original Enphase m215 micro-inverters connected to AC-out-1 which I manually switch on and off to prevent the m215's pushing the voltage too high when the batteries are fully charged. I have tried setting the PV inverter assistant, but I think the m215's are so old they cannot limit their output on frequency shift.

As this whole system is off grid I would like to connect the m215's to the currently unused AC-out-2. I would like to know if I can configure the internal relay which switches AC-out-2 on/off depending on the grid being detected at AC-in-1, so that it switches on/off based on battery SOC.

Any advice would me much appreciated.

mp2nz asked
shaneyake answered ·

2 Answers

Limit battery oscilations with ESS


I have a 3 phase MPII setup with AC coupling (fronius symo) on AC OUT, grid feed in is allowed

I use a small battery bank (I know, but a larger bank is not economical at this point.)

I need the system to use the grid for surge loads (e.g. switching on of induction cooker ) not the batteries!

It makes much more sense to draw 3kw for 10-30s from the grid than from the battery.

If I use scheduled charge during the day with a low SOC (when I expect the batteries to be charged from AC coupled PV) the surges still are drawn from the battery if minimal SOC is below current SOC, so this is a NO GO.

If I limit the inverter power to 0 during day, it wont invert surplus PV power from e.g. L1 to L2 if there is surplus.

My current idea is to use node-red and gradualy increase minimum SOC as the battery is beeing charged, so that it is always 2-3% above current SOC, this enables maximum inverter power between L1/L2/L3, disables battery discharge and enables battery charge from surplus AC coupled PV. And is AC coupled PV is not enough to power loads, grid will be used.

Then, at night, I will drop the minimum SOC to 40% and the battery will be gradualy discharged till morning with a constant draw of 300-500w.

Any other ideas?

Thank you

michal-kubina asked
shaneyake answered ·

1 Answer

Behavior of Multiplus II with AC coupling on input

My current system consists of a grid tied Solis PV inverter and ~4,5kWp of solar. My main focus today is to compensate my grid consumption over day. Additionally I'm charging an EV when there is excess solar power available - I'm steering this based on grid-meter data with a Raspberry PI.

I want to enhance the system with a Multiplus II and a batterie now.
After reading tons of documentation and watching videos, I'm not sure about the exact behavior of the system in case I would connect the PV inverter on AC input of the Multiplus II.

My current understanding would be the following:

  • The existing AC PV inverter will directly power the loads as today
  • In case the Multiplus detects negative consumption (feed-in) at grid meter, it will start to load the battery - aiming for zero consumption at grid meter
  • If the batterie is full, all excess power from the PV inverter will be fed into the grid as the Multiplus is not taking any power
  • If the Multiplus detects positive consumption at the grid meter, it will provide power from the battery (if possible) and aim for the grid setpoint (e.g. 0W)

Is this understanding correct?
Would I need to install the ESS assistant in this case or do any other configuration?

force-1 asked
petr answered ·

1 Answer

ESS, AC Loads, Grid Meter, Multiplus


1x Multiplus-II AC In (AC Out not connected), EM24 gridmeter, Fronius PV Inverter, Venus GX.

On the remote console the Multiplus AC Power is always included in the AC loads.

for example the Multi is charging the battery with 1kW and the house consumes 500W, AC Loads is 1500W. AC loads should show only the house consumption w/o the Multiplus power...?



lars78 asked
Tom Büschgens commented ·

3 Answers

Grid-tied Multiplus 2 with AC coupled PV - how to connect

Hi, I've seen a schematic of a grid-tied Multiplus 2 with AC-coupled PV array. But how do you connect the grid and the PV ac to the Multiplus. As I understand it, the grid would normally connect to AC-in, which is in fact bi-directional. But that only leaves me with 2 AC-outs. Where do I connect the PV AC output?



andymcw asked
andymcw commented ·

1 Answer

AC Coupled ESS minimum battery size


We are installing a AC Coupled 3 Phase ESS (Grid Connected) system with 15kW 3P Fronius connected on Output of 3 x 5kVa MultiPlus II. Were planning on installing approx 30kWh of BYD lithium, however i noticed on the Victron AC Coupling & Factor 1.0 rule page there is also a minimum battery size required. (in this instance it is 48kWh)

Can anyone explain this?

30kWh of BYD will deliver 30kW of power & accept up to 20kW of charge.
If the PV inverter was on the Input of the Multi the minimum battery size 3 x 2.5kWh modules acording to the Victron/BYD guide.



Nick Gillam asked
Daniël Boekel (Victron Energy Staff) commented ·

4 Answers

Configure ET112 as PV Meter on AC Out

Switched from a MP2 5000 Single-phase AC IN setup to MP2 5000 3 phase AC IN / AC OUT setup today. Using an ET112 on L1 as PV inverter meter usage. I cant change it from AC 1 to AC Out in Venus. When I select AC Out it jumps back to AC IN 1. Where my issue?

marcmarin asked
rennmoehre commented ·

1 Answer

Multiplus trips in inverter mode, why?

I have a Multiplus and Fronius AC coupled on AC out1. Li-ion Batteries.

When grid fails the inverter takes over.. Fronius continues. as soon as the PV power is higher than the load everything trips, including the ccgx. then the inverter starts up again and restores power on AC out 1. Primo sees life and switches on... bang, everything trips.

if i add a load the the system (heater) then everything is ok. The frequency shift is set up correctly. maybe just not fast enough to reduce pv so that the inverter stays inverting.

So can this system not work in my configuration? using the excess pv to charge while grid is off? Seems as soon as the multi changes from inverting to charging the fronius loses the supply it is latched to.

Keith Arnold asked
Harry Petrakis answered ·

10 Answers

AC coupling with Kostal PIKO 17 possible?

Hi all

I'm currently planning a 3-phase Victron Multi-Plus II 48/5000 ESS system as an addition to an existing PV system with a Kostal PIKO 17 inverter from 2017/2020 (2017 model replaced in 2020).

I'm unsure if this combination works, i.e. if the Kostal PIKO can handle the frequency shifting described in the MP2 docs if it get's connected to AC-out1 and the grid goes off.

Does every inverter lower its output when "grid" (in this case the MP2's grid) frequency arises?

Is there any experience with AC-coupled Kostal PIKO inverters?

Many thanks

chergyro asked
chergyro answered ·

1 Answer


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