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Thread: Paralleling of Inverters

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    Paralleling of Inverters

    I need help with this.

    How can I parallel 02 or more inverters of equal rating feeding a single load.

    Can someone suggest with brands and circuits.

    Thanks

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    Quote Originally Posted by greggs007 View Post
    I need help with this.

    How can I parallel 02 or more inverters of equal rating feeding a single load.

    Can someone suggest with brands and circuits.

    Thanks
    Assuming you mean solar PV fed inverters, here's a link that may help.

    http://www.freesunpower.com/inverters.php

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    Similarly to how you use combiner boxes to parallel multiple strings.

    Inverter one (500kW @ 480V) AC output can backfeed an 800A CB in a 1600A switchboard. Inverter two (500kW @ 480V) AC output can do the same. The line side of the 1600A breaker can now be interconnected to your service.
    If you can't fix it, fix it so no one else can.

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    I would say that this is only possible if the manufacturer specifically says you can and provides a wiring procedure. Personally, I wouldn't shoot from the hip on this one.

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    The approach I mentioned earlier is the common method for combining inverter AC feeder. I have built many multi megawatt systems where the inverters backfeed into a piece of gear that then backfeeds an existing service.
    If you can't fix it, fix it so no one else can.

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    Quote Originally Posted by SIRSPARKSALOT View Post
    The approach I mentioned earlier is the common method for combining inverter AC feeder. I have built many multi megawatt systems where the inverters backfeed into a piece of gear that then backfeeds an existing service.
    Were they line commutated inverters?

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    prior to the development of PV systems, stand alone inverters could not be paralleled without a sync connection between the inverters, this sync connection allowed both inverters to run off the same oscillator from the master inverter that would keep both inverters in sync to allow a double of voltage if connected in series, or a double of current if connected in parallel, most stand alone inverters do not have this connection, Triplet offered a few models back then Which I have a pair of 3600 watt units, most only had an independent oscillator in each unit to provide a 60hz reference signal from.

    Now with the advent of PV systems most inverters designed for PV use will have a sync system.
    Wayne A. From: N.W.Indiana
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    Just don't be fairly safe

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    Inverters that supply a load such as a variable speed electric motor can not normally be paralled, a single unit unit of suitable size should normally be selected.
    Some power inverters, but not all types, intended for off grid homes can be parralled, follow the manufacturers directions in such cases.
    PV or wind turbine inverters that feed energy back into the grid are easily parraleled, after all how does the grid "know" the difference between two inverters in your home, and one in your home and one in your neighbours home, both on the same POCO transformer.

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    one reason it is a lot easier to connect to the 'grid' is it is only 60hz: its pretty easy to make a good output filter at ONE FREQUENCY. Now try that for a vfd that outputs 0-1000hz! A zillion times harder, and in fact, probably not possible to economically make a one size fits all filter that would clean it up enough for connection to the poco grid at any freq in its range if that were required.

    So the semi nasty output switching of multiple vfds connected to one motor is hard to accomplish and so not done often. In addition, most vfd's don't have much output impedance in series so their directly connected IGBTs would turn on into the other vfds IGBTs and things would smoke quickly. We do this with Refu drives with a high speed fiber optic interface and we sync the IGBT PWM pulses so all connected drives operate the transistors at the same time.

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    Quote Originally Posted by greggs007 View Post
    I need help with this.

    How can I parallel 02 or more inverters of equal rating feeding a single load.

    Can someone suggest with brands and circuits.

    Thanks
    Grid tied PV inverters are routinely paralleled simply by combining their outputs in a load center. Their current ratings (the same or different) do not matter.

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