Gary,
The "simplistic" approach is to use the voltage /frequency droop method. As
the output current rises, the output voltage and frequency drops slightly.
You have to target a slightly higher voltage & frequency initially. (A
series resistor would do the trick wrt voltage but wastes power, electronic
voltage control is really required).
You still have to closely monitor output current and voltage to remain in
phase. If you have a voltage supply that is noisy and/or variable (eg  a
genset) then you can have real problems.

Even running a number of inverters in parallel can be difficult without
additional communication & sync lines.

If you look at how the phase difference between the voltage and current
then a leading current phase angle will indicate that you are running
slightly faster than mains, while a 0 phase shift with high current
indicated that the output voltage is high.

In any event you will probably need a disconnect/connect relay to alow
syncronisation before you start feeding power and an electronic current
limit to limit current quickly and safely in the event of mains failure/
phase reversals etc.

If you do find an easy solution I would be very interested in hearing about
it!

Richard P




Guys,

Anyone have information on grid-tie inverter schematics?  Something that
will synchronize to the grid and allow someone to put power back on the
main grid?  Input= ~12V, Ouput =120V, 60Hz, up to ~1kw.

I can find stand alone inverter schematics, but not grid synched.

I know there's all kinds of safety issues, so please skip the flames.  Just
trying to get educated.

Thanks,

Gary

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