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3 Phase inverter vs unbalanced load

  • 12-12-2022 8:17am
    #1
    Registered Users Posts: 527 ✭✭✭


    Hi,

    A question for those of you with 3 phase inverters / anyone who knows the answer. I was watching a youtube video last night from Artisan Electrics and they were examining a commercial premises with 3 phase power & has solar PV. They were sizing a battery and explained that if one of the phases was drawing more current than the others, the battery has to discharge at the highest rate across all 3 phases, ending up exporting some to the grid! Not something I'd ever expected or considered. They considered installing 3 x single phase inverters with a battery each, the batteries sized to the unbalanced loads across the 3 phases. Now they'd have 4 inverters! My questions are as follows:

    If I had 6kW of Solar Panels and a 6kW Hybrid inverter and I plugged my car in: phase 1 had no background load but had the car charger on it, phase 2 & 3 each had 1kW background load, would I get 4kW into the car & cover the background load on the others, or only 2kW to the car the background loads covered BUT 2 x 1kW would be exported so it's "balanced"? If it's balancing the PV power between phases, is there any meter balancing occurring so that the import of 5kW on phase 1 to give me 7kW to the car is negated a bit by the 2 x 1kW exported to the grid or is that export completely wasted? Am I paying for 3kW or 5kW import from the grid in this case?

    For the Battery, if I have an air source heat pump in the dead of winter and there's no solar being generated, let's say my 20kW battery is full from off peak charging. Phase 1 & 3 have a 1kW background load each and Phase 2 is drawing 4kW to the ASHP. Would my battery be exporting 2 x 3kW on phases 1 & 3 while satisfying the 4kW on Phase 2 so it'd drain by 12kW in the first hour (2 x 1kW background load, 1 x 4kW ASHP, 2 x 3kW exported), and the battery would be drained after 1.5 hours with 10kW or so dumped to the grid. Is that the case?

    Obviously balancing loads is vital in 3 Phase setups but certain loads can shift the status quo easily so I'm trying to gauge the worst case, how an inverter would respond and then how to design a solution around this problem without reverting to single phase options / mains feed. Thanks!



Comments

  • Moderators, Home & Garden Moderators Posts: 5,487 Mod ✭✭✭✭graememk


    Seen the same video.

    I would need to do some reading to be sure but my understanding is that 3 phase inverters (hybrids too) don't try and balance the power between phases. Open to correction here!

    Another thing not mentioned, is that the solar inverter does the same. Puts the power out equally to all phases.

    If they put a bigger battery on phase 1, most of the excess solar will be gobbled up by the use on phase 1 and still won't have enough excess to charge the battery.



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