most 'generators' ( alternators ) are making ac ... pretty much the same way your car makes it.. pretty much same principle of ac generation the way the power company makes it. spinny parts and magnetic fields.
now 2 stage that and throw a battery and thus dc right in the middle.. charge battery, then use inverter to make ac.
get some benefits like stand by ac that, when load is low, can have the ac sourc 'trickle' and the engine not run lock step rpm to make a certain rpm/hertz... the electronics in the inverter side handle making the correct freq. etc.
there's more to it than that.. but that's the verbal 'block diagram' of it.
soundguy