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Forum Index : Solar : VFD's and 3 Phase inverters.

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Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1582

Posted: 11:00am 30 Sep 2022

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I have seen that 3 phase to single phase inverters are quite cheap now. Similarly I also see quite a few 3 Phase solar inverters going cheap.

I am wondering if I could run a 3 phase solar inverter to feed a 3 Phase to single phase VFD?

Would the VFD have any power present at the input end when connected to the single phase AC line so the inverter can do it's checks and synchronize?

Be nice to be able to use some 6-8 KW inverters that are going for a few hundred bucks.
Seen a few NOS units going for this sort of money.

Jacob89
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Joined: 10/09/2017
Location: Australia
Posts: 39

Posted: 05:14am 06 Nov 2022

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If I understand you correctly, you want to backfeed three phase from the grid tie through the VFD and then be backfeeding single phase from the VFD into the grid?

As I understand it VFD's essentially have 3 H-Bridge inverters that each produce one phase, from the DC that is rectified from the incoming single (or three) phase input.

I would guess the H-Bridge would be capable of passing current in either direction. But whether the brains of the VFD would allow it to produce an output with out a motor connected, for the grid tie to sync to, I don't know. Maybe you could fool it by connecting a small motor in parallel with the grid tie.

All thats academic though, the real problem is that the DC you'll get from the grid backfeeding into the VFD H-bridges, needs to be converted to single phase AC. You'd need to replace the rectifier stage of the inverter with another inverter.

As well as that, the majority of the cheap VFD's I have seen only output 240v phase to phase, when you feed them 240v single phase input. I would think all the three phase grid tie inverters you would find in Australia would be looking for 415v phase to phase. There are some I have seen more recently out of China that step up 240v single phase to 415 (220v to 380v actually, as I guess they're mostly intended for the Chinese domestic market).

Much easier to collect a couple more single phase grid ties. I picked up a brand new in box 5kw unit for $150 the other day.

Bryan1

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Joined: 22/02/2006
Location: Australia
Posts: 1395

Posted: 06:54am 19 Nov 2022

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6-8 Kw for a few hundred buck ....... where is the links man as I do need a new inverter for my shed so I can finally use my mig

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