at the most basic level, an inverter consists of an oscillator that toggles a transistor on and off, switching the battery volatge on and off, generating a square wave between 0-144V (the AH is a 144V battery, right? A transformer and followon inductors and capacitors smooth the wave into a sinewave if necessary for, say, motor operation, and step the voltage to whatever is needed for operation.

I am very sure that much more sophisticated means are used by Honda, but thats the guts of it there. More transistors can also be used to produce multiple square waves of different amplitudes, mimicing a sinewave right off the bat.