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abner-grech avatar image
abner-grech asked

AC coupling and micro grid/island grid installation

Hello. I live in the sunny island of Malta in the middle of the Mediterranean Sea. My home is set up with two grid tie systems, one has a steca 4200W inverter and around the same power of panels attached to it and the other has a Kaco 4202 inverter with also the same power of panels attached to it. The systems although quite old work flawlessly and I have decided to upgrade them by adding a Victron Multiplus 2 and a 200Ah Lithium Battery to each. I managed to connect everything and set up the Multiplus with the ESS using VEConfig tool and the batteries charge and if mains goes missing the Multiplus switches to Inv mode and powers all the house but both the Steca and the Kaco inverter stop working showing an over frequency alarm. I changed to Steca Inverter grid setting to island grid and it seems that it would like to work but after a few seconds working it still gives the over frequency alarm and stops working. Any help please?

AC PV Couplingmultiple invertersfrequency
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matt1309 avatar image matt1309 commented ·

Hi @fabian-lauer


I'm not familiar with those grid tied inverters however when you setup ESS in VEConfig did you setup frequency shifting and if so what frequency did you enter?

I can see a fronius example on victron website but the frequency limits of your grid tied inverters may be slightly different but my guess is these settings are the cause.

Some grid tied inverters let you input the frequency limits so they match the ones entered in victron. Some dont so you have to use larger ranges in victron settings then and just hope you exceed the prebuilt settings in the grid tied inverters.


Might be worth checking with the provideres/manufacturers of the grid tied inverters. Some companies call the feature something else victron calls it frequency shifting.


AC-coupled PV with Fronius PV Inverters [Victron Energy]

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lifeingalicia avatar image
lifeingalicia answered ·

Hi

did you adhere to the 1.0 rule ? Ac coupling behind multi should not exceed the multis capacity....

This limit is called the factor 1.0 rule: 3.000 VA Multi >= 3.000 Wp installed solar power...

One reason is that the multi can only switch up to 32A on grid failure and it may take a couple of moments to regulate frequency during which excess is pushed into the battery as it has nowhere else to go. So imagine sunny day bat is full only 100W load solar produces happily 3Kw+ and grid fails .....

With 4200W solar I do recommend to feed the AC before the multi and install a switch over if large grid fails are expected or split some solar off.

Like Matt1309 said check the frequency demands....


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abner-grech avatar image
abner-grech answered ·

Sorry my mistake not to mention that I have the 5000 VA Multiplus

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abner-grech avatar image
abner-grech answered ·

Also I did not touch the ESS frequency settings as the setting on my Steca Inverter are higher (56 HZ) then the Victron and so it has a wider acceptance. When the grid fails the Victron shifts to inverter and the Steca restarts and works for a few seconds also accepting PV input then the Victron starts making a contactor clicking sound every 30 seconds or so and the Steca gives the over Frequency alarm. It is clear that there is something else triggering the steca to stop working and it is not necessarily the frequency as if it was so then the Victron would stop too as the over frequency limit of the Victron is much lower then that of the Steca. Any input?

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matt1309 avatar image matt1309 commented ·

Hi @Abner Grech

I think you're misunderstanding the frequency shifting we're refering to. It's not the supported input levels of the inverters it's a feature victron uses to communicate to grid tied invereters/turn them off if they need to.


It's used to communicate to Grid tied inverters in a micro grid like you have them configured. Say your batteries are full and the grid is off, the grid tied solar needs to be told to turn off. Otherwise you'd overload the system with power. ie there's no where for it to go if your battery is full and the grid is offline.

Victron uses frequency shifting to change the frequency of it's output to cause the grid tied inverters to turn off (Steca).

So what we think is happening in your scenario is you've not setup frequency shifting so as soon as grid goes down victron shifts the output frequency to above Steca's levels to force it to turn off. Once you've configured the Frequency shifting settings in ESS the shutdown of the Steca should only occur when the grid is off AND the batteries are full in order to prevent overloading the system.

Hope this helps.

Steca may have additional frequency shifting settings in their settings for just ramping down output. Victron also has that setting so you could set it up so say the output from victron is 52hz (random number i've picked out of nowhere) and it'll inform Steca to ramp down but not turn off and then another limit is set for turn off



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sharpener avatar image
sharpener answered ·

I have Steca inverters (2x StecaGrid 2000) on the AC-Out of my Multi 5k, and with the following settings in ESS Assistant they work OK in island/grid failure mode. When the battery is full the Stecas trip off on overfrequency until it is discharged a bit, then resynchronise automatically, with a cycle time of about 10 mins. Maybe this will work for you too:

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abner-grech avatar image
abner-grech answered ·

Hi @matt1309 Yes I do understand now what you mean and it makes logical sense. It is a fresh installation and I always tried the system with batteries on full capacity and obviously the power has nowhere to go. I will drain the batteries and try the system again. Thank you @sharpener for the hints. Much appreciated guys. Well done for the service. Keep it up.

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