Cascading inverters

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Phil Gavin asked Oct 18, '18

Cascading inverters

Already posted this at Victronlive, but it seems like that is transitioning to this forum, so posting here as well.

I have an existing 48V 5kVA Quattro fed DC from 13.5KWp PV and 1200AH battery bank.
Power cuts are not infrequent and I have islanded some essential loads to be purely fed from this system.
I want an offgrid system, and I'd prefer not to add ESS unless I have to.

I want to add another identical Quattro to the system and add some less essential loads.

I understand how to conventionally parallel them.
And that it will effectively give me a 10kVA Quattro, but only the same features as I already have.

Q1. I would like to know if connect them in and upstream -downstream relationship would that give me the ability to have 10kVA available at the downstream inverter and the ability to loadshed one of the AC outs if my battery SOC was low. As I now would have 2 AC outs.

Q2. Would this also give me the ability to have a second battery bank that be configured to use a different DOD?

I realize the downstream inverter should not feed back power to the upstream inverter as the downstream inverter will not respond to a frequency rise like a Fronius PV inverter, if the upstream battery bank was full, the feed-in power would have nowhere to go.

Q3. Assuming this configuration is feasible. Would it exclude the addition of a Fronius PV inverter on the respective AC out of both inverters? I may add 5VA of PV inverter at each level of AC out, (1:1 rule applies), but because the everything is synced at the upstream inverter's frequency, it would appear that the 1:1 rule is now broken, is this permissible in the settings?

Q4. Assuming a single battery bank and no additional PV inverters, for the moment are there any special setting requirements and which assistants would be best suited to achieve this?

Thank you

cascading inverters

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Guy Stewart (Victron Community Manager) ♦♦ commented · Oct 18, 2018 at 01:09 PM

Hi Phil,

I will try to answer.

Please try to keep 1 question per post, it will make this site a lot more useful as a reference in the future.

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Guy Stewart (Victron Community Manager) answered · Oct 18, 2018 at 01:12 PM

Q1)

In theory yes, you will get the additional power delivery of the second inverter, and the PowerAssist from the first.

In reality, a correctly installed parallel configuration will provide better balance with less chance of overload.

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Guy Stewart (Victron Community Manager) answered · Oct 18, 2018 at 01:15 PM

Q2)

Yes, A second independent Quatrro can use a seperate battery bank, and have different parameters around its depth of discharges.

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Phil Gavin answered · Oct 18, 2018 at 02:09 PM

Local support is impractical option.

On the other hand, I've been commissioning protection relays an the electrical systems around the world for 30 years. And in that time I've had to become expert on many a system.

I 'll parallel them conventionally for now, and enroll myself on some Victron training and reconfigure them in the future.

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Modifications Space

Node Red Space

Answer 1 · 2018-10-18T13:18:13Z

Guy Stewart (Victron Community Manager) answered · Oct 18, 2018 at 01:18 PM

Q3)

No, you may not add a potential AC generator supply that is greater than the capacity of the inverter charger to its outputs (1:1 rule). Doing so will run the risk of damage, it is not worth it, and it is definitely not supported.

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Phil Gavin commented · Oct 18, 2018 at 01:46 PM

I think you misunderstood my question here.

The 1:1 rule wouldn't be broken if 5kVA was added at the AC out of both stages of quattro.

Both could dump 5kVA back into the battery.

However because everything is synced to the upstream inverters frequency, it would effectively be reducing 10kVA worth of PV inversion.

So it would appear as if it was breaking the 1:1 rule, which it wouldn't actually be doing.

My question was is the 1:1 rule an imposition of the "VE configure" software or can I overule it?

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Answer 2 · 2018-10-18T13:19:38Z

Guy Stewart (Victron Community Manager) answered · Oct 18, 2018 at 01:19 PM

Q4 )

There are many ways to set up this configuration depending on the behaviour you want. This is considered an advanced design, you should have experience with Victron equipment, VEConfigure and a local distributor who is willing to support this before going ahead.

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