how does a grid tie inverter work?

[cardamon]

How does a grid tie inverter control how much power it is feeding into the grid?  Does it phase shift the output waveform slightly to get a variable difference of potential?  Also curious, can a typical grid tie inverter feed and synch to a variety of "non-pure" forms, like from a generator or even modified sine wave?  I think i remember reading that they typically have a frequency tolerance where they will shut down if the frequency is too far off, but what about the waveform itself?  Not only am I just curious, but also just wondering if it is possible to "trick" ,say, a windy boy into working off grid (without buying a sunny island)?

[boB]

Typically, you just superimpose your generated sinewave with that of

the grid and then "try" to bring UP the voltage of your generated sinewave,

and the power "flows" towards the grid. ("Power flow" is not exactly a technically

pure wording but even the power industry uses that term every day)...

The reason they cut off if the frequency of the grid goes too far off is

due to the rules from UL1741 standard and IEEE1547 so the inverter doesn't "island"

and hurt the lineman...  Even though the typical inverter and system of less

a few kW would not be able to drive the pole transformer and much less, the whole neighborhood without (most likely) turning itself off anyway.

Tracking a generator is done quite often and is called "Generator support".

You can take something like a Sunny boy and connect it to the output of say,

an OutBack FX inverter and have the FX operate as the "grid" but you have to

be careful of when the loads are small and the output of the inverter

and also the battery voltage rises.  In that case, you should add load diversion

or some kind of switch to turn off the Sunny Boy (or equivelent).

boB