DC to AC converter synchronization with power grid.?

If you have designed a simple circuit for converting 48VDC to AC 120VAC, it will be just that: namely a simple circuit.

When you try to match the phase it will be more complex, but still not difficult.

Of course you need to sample the line AC first with a scope, and add your converted AC (from the 48 V) to the grid at the zero crossing point, both ways, when going negative and then 180 degrees later when going positive. The "added" power is only use full when both are in phase, otherwise they cancel each other out

So, you need a trigger circuit that will take care of that.

Home brew your own with some SCR's, cheaply available at any electronics's store.

If you are looking to sell power back to the electric company they require you to buy specific equipment to handle the interface. For most people it is too expensive but I have heard of celebrities like Daryl Hannah who have done it.

If you just want to supplement your home power then you could have a few isolated circuits on your own power. Incandescent lighting would be a good application incase your waveform varries a little it wouldn't hurt anything.

I would suggest having an electrician wire your supply into the circuit breaker you want to run.

First you'll need to get you a phase sequence meter or use a duel trace 0'scope to check wave forms make sure they are same.

Nest you are going to need to design a trigger circuit for both your positive and negative going wave forms from the grid.

A good way to start is using a push pull complementary amp triggering circuit using NPN transistors to trigger on positive going wave form and PNP transistor to trigger on negative going wave form from you in coming power.

Or. you can use positive and negative gated SCR's as your final out's on the inverter you are building.

Another way you can do it is use a single transistor amp. circuit using coupling it both at the emitter (in phase) emitter follower and collector (out of phase) collector follower. to couple into the PNP and NPN transistors in your complementary driver amp.

Hope that gives you some ideas.