AC Coupled Microgrid

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taylortops asked Jul 12, '21

AC Coupled Microgrid

I'm looking at organising the system like this (pictured):

The RS on the Shed would be the master system (grid forming) with big battery, and the other systems would have only minimal battery. The 'morning sun' place has a little cabin but no battery. The loop at the centre is the micro-grid (to be considered unreliable). Also, there's no town power.

Is just AC input current monitoring on the Multi's enough or do I need to get more sophisticated? Anything else I should be thinking about?

Notes: -Shed would have a Cerbo as well. -I'm not looking to DC couple the systems.

Multiplus-II EasySolar All-in-One

barraba-1.jpg (113.9 KiB)

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Modifications Space

Node Red Space

Answer 1 · 2021-07-12T02:45:51Z

Guy Stewart (Victron Community Manager) answered · Jul 12, 2021 at 02:45 AM

Hi @TaylorTops,

Interesting project. Generally speaking it is not advised to feed the AC output of one Victron inverter into the AC input of another one. I have seen it work, but also been told that it is not recommended, so I presume there have been issues in the past. Though it would also not have been done before with the new RS range, so I would treat this as new ground, and all the potential risks and unknown unknowns that come with being a pioneer in power electronics.

What are your intentions for the microgrid?

The EasySolar and Multi2 will not have any way to tell if there is 'surplus' available from the RS / Fronius - so if it is intended as a backup of last resort then it could work. That is you want to have an automatic and non-generator supply available to guesthouse and house if their batteries run low.

The AC output side of the RS is limited to the 1:1 rule, so I would definitely not be expecting to PUSH/export power back from the Guesthouse and House to charge the RS Shed (at anything above a trickle), as the Fronius has the potential to already reach that capacity 6kVA capacity.

What was your programming intention? To set up the Multi-2 and Easy in ESS mode with 0 export, or program and Ignore AC parameter to close the AC input contact when battery is at low SOC? Or something else?

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shaneyake commented · Jul 12, 2021 at 03:10 AM

@Guy Stewart (Victron Community Manager)
I know this is not a supported config and can have problems however I have a very similar setup that has been running for 4 months without any issues as an experiment. Someone has to be a "pioneer in power electronics"

As I mentioned in my comment. Control is critical, I have data lines going to all the GXs and control the grid set points of the slave sites to balance the load and to move power from one unit to the next.

The 1:1 can be ignored to some extent as with control you can guarantee that you won't push back more than 6kVA at any given time. My system doesn't have any AC coupled PV which does make things easier. This design will be harder as the AC coupled PV could max out the 1:1 which won't be ideal as managing the reset of the system and not tripping the RS could be tricky.

Inverter setup is pretty easy ESS like normal but can't use LOMs (The frequency shift from LOM causes all kinds of problems, tried a bunch of diffrent configs but ultimately makes everything very unstable, master can use LOMs and I rely on that to disconnect whole system from grid.), I then run ESS Mode 3 with NodeRed controlling ESS for every site. My system is grid connected most of the time but have 3-4hours per day of no grid, best problems I have found were when we lose grid is causes all kinds of random things to happen but then after a few minutes the microgrid is stable and all the slave sites rejoin. Seems like UPS option shouldn't be used on slave sites if main site has grid, solved this problem mostly but won't be an issue here.

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Answer 2 · 2021-07-12T02:50:21Z

shaneyake answered · Jul 12, 2021 at 02:50 AM

Hi @TaylorTops,

I actually have a similar setup.

The main problem you have is that you can't throttle the Victron Inverters via frequency shift alone.
You will need a data connection, fiber or ethernet to the GX devices.

There is a lot of little things to get this to work, I have also implemented load balancing on my system so that all batteries are at the same SOC.
In my system I have a NodeRed controller that is controlling the whole system. Load balancing and throttling down the PV when the Master/Shed batteries start to get to 100% to prevent overcharge.
Load balancing also allows the PV on any building to be used anywhere else.

I wouldn't use the RS 48/6000 but rather a multiplus-ii 48/5000 and 450/100MPPT. The RS 48/6000 doesn't have all the features of the Multiplus-ii yet, especially when it comes to external control and can be paralleled at a later stage.

This is a pretty complicated setup but will defiantly work, don't think it is supported by Victron.

If you need help with this project or would like a call, please email me at shaneyake2 @ gmail.com

Thanks,

Shane

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