On-Grid Solar Inverter works in which principle?

The main purpose of Grid-Tied inverter is to share the load with Utility power. If load is less then the power of Grid-Tied inverter then the inverter returned the power to the utility power acting as a generator. Which results the reduce of electricity bill or reverse meter.

can any one help me that " Which principle Grid-Tied Inverter works?".

I just need a block diagram.

Tied grid inverter work in parallel with grid and if load in low and grid accept power injection, inverter will supply power in grid. BUT, in most county, this working mode need to be notified and accepted by electricity provider. In most case, invert will supply locally loads that need power; locally mean same small network that cover all load from one transformer phase (if is single phase inverter). I there are no loads on this network, voltage will increase and grid will shut-off when reach a limit imposed by electricity company.

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"I there are no loads on this network, voltage will increase and grid will shut-off when reach a limit imposed by electricity company."

Sorry, correct is

If there are no loads on this network, voltage will increase and inverter will shut-off when reach a limit imposed by electricity company.

If there are no loads on this network, then the voltage will increase to the solar panel's open circuit voltage which is probably a lot less than the electricity company's limit, but still the inverter will turn OFF because commercial grid tied inverters have a minimum load setting and are not active below that.

In simple words, you can say that a grid tied inverter is a true sine-wave inverter with the ability to synchronize itself to the grid.

here's something that confusing me if i measure the AC output to determine the grid voltage and then synchronize to that voltage.. how do i know i am not synchronizing to the inverter voltage!? before startup it is obvous, only voltage at the point of common connection is the grid.. but after inverter starts up.. how do you tell the difference?

and this from a guy who actually built a grid tied inverter with MPPT, lol. when i built my proof of concept, i had a separate transformer plugged into the wall is where i got the reference voltage from.. i was not measuring at the inverter AC output.

before startup it is obvous, only voltage at the point of common connection is the grid

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No. You always observe a loaded grid voltage, never open circuit. There are other linear and non-linear loads connected to the grid before the grid tied inverter is switched on. It doesn't make much difference if the connected devices consume power or feed power to the grid, all are causing a variation of the grid voltage, amplitude and possibly waveform.

A grid tied inverter should be controlled to source a sinoidal current in phase with the fundamental of the grid voltage, in other words pure real power.

Normally a GTI operates as a voltage-controlled current source, much like an active PFC controller but sourcing current instead of sinking it.

ahh.. that makes sense. the inveter's output voltage is noway going to change the very strong grid voltage/frequency. so.. when you measure the 3-phase output voltage you see basically just the grid voltage (and all its loads & sources). that makes sense. then the idea is to measure that voltage so you can use it as a reference sinewave such that your inverter output current is in phase with grid voltage (i.e. your measured reference signal) give or take some lag. power factor control can be controlled by delay or advance of the reference signal which then causes the phase current to lag or lead grid voltage. i built one of these years ago and did not fully understand that concept. seems a bit obvious now