question

Frank avatar image
Frank asked

Frequency instability on AC OUT of Multi-II

Hi, I have the following AC coupled configuration

design-2-page-001.jpg

The 2 PV arrays are IQ7 Enphase micro's at each panel

The 2 Multi's are 48/5000/70-50 and are configured with ESS assistant and frequency shift capability according https://www4.enphase.com/en-au/support/ac-coupling-enphase-microinverters-grid-applications.

The battery system is 500Ahr


The problem I am having is that the frequency of the AC OUT of both Multi's is continuously jumping from 50 to 53 Hz (approx. every 5 - 10 sec.). The IQ7's don't like this and report frequency/grid instability errors and therefor don't produce any power. They work fine when directly connected to the grid. Battery still 60% SoC but getting lower as we speak, because there is no charge.


Please help me resolve this issue ? Why is the frequency jumping ?

Multiplus-II
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6 Answers
Alexis Kalogerakis avatar image
Alexis Kalogerakis answered ·

I have the same issue with two difference systems.
1 phase MultiPlus 24/5000 with Fronius Primo
3 phase Quattro 48/10000 with Fronius Symo

Hope we will have a answer from Victron's stuff.

https://community.victronenergy.com/questions/206690/quattros-frequency-shifting.html?childToView=209934#answer-209934

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Frank avatar image
Frank answered ·

I now have the solar PV inverters turned off and the Multi's are still jumping frequency between 50 and 53 Hz. There is nothing unusual on the load side i.e. some lighting, laptop chargers etc.

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Frank avatar image
Frank answered ·

Standing next to the inverter I can hear the quiet hum changing pitch in step with the change of frequency on the Cerbo display

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mondeoman avatar image
mondeoman answered ·

The placement of the current sensors doesn't seem right...

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Paul B avatar image Paul B commented ·

I suspect6 these are AC current sensors and are used to measure the PV inverters outputs

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Paul B avatar image
Paul B answered ·

Maybe try the Back to Basics approach

The Frequency will only shift if the AC input is disconnected or the multi ac relay ois off - as the mult's CANNOT override the grids frequency as the grid is to powerfull

then when the grid is OFF - check at what battery voltage the frequency is changing at.

The frequency should only change when

1. THE Battery BMS says the batteries are full or one cell is full. (you dont mention this in the disctription and how its connected in the diagram.

2. or the settings in the ESS setup are met

3. or how the DVCC max voltage is reached.

4. or the batteries are full ie the Bulk voltage is reached

at any one of the above and the gid is off then the multis will increase the hz up to the freq set in the ess assistant setup.

Suggest you go over the full ESS setup again.

https://www.victronenergy.com/live/ess:quick-installation-guide



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Frank avatar image
Frank answered ·

Hi,

Because the system is configured as ESS and battery is half full, it is running in inverter mode, i.e. it is not taking any input from the grid.

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Paul B avatar image Paul B commented ·

maybe its saying SOC is 50% this does not mean the soc is correct - but what is the battery voltage and the ess settings.

it will only change freq if the system thinks the batteries are full and this is all done in the settings

DVCC

charge voltages

ESS settings

you have to work out what is triggering the freq change. then you have a chance of correcting the issue

Also if you have a BMS connected then it will shift if the BMS gets a High cell voltage warning.

I use this setup and it works great, the freq only shifts if there is a overcharge issue and not enough consumption



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