"Inverter Generator" is some product manager's form of a joke. He thought it would jazz up the sales brochure and give the salesmen something else to talk about which as usual they are totaly ignorant about.
There may be some exceptions, but automobiles use a "3-phase alternator" and a "solid state rectifier" that outputs a nominal 12 Vdc. Actually 13.5 Vdc when charging.
Back in the 60s and 70s, the Cadillas Fleetwood 75 limousine had a Alternater that not only produced 12 Vdc it also produced 115 Vac. It was there so the occupants could run their electric shavers and hair dryers so it only output about 350 watts. Nothing useful at all.
I disagree on the product manager stuf -- There is a real and fundamentally different animal in the inverter-based vs conventional generators.
Here is Honda's explanation:
"First, the generator's alternator produces high voltage multiphase AC power. The AC power is then converted to DC. Finally the DC power is converted back to AC by the inverter. The inverter also smoothes and cleans the power to make it high quality. A special microprocessor controls the entire process, as well as the speed of the engine."
The inverter-based generator
(IBG), relatively new in the market in the last decade or so -- Since the frequency is produced by the inverter electronics, the engine can be run at any rpm sufficient to supply the actual Wattage for the load. Generally they can only be found in relatively small sizes, 6.5KW or less. There may be an upper limit to inverter technology preventing larger generators.
"Portable engine-generators may require an external power conditioner to safely operate some types of electronic equipment. Small portable generators may use an inverter. Inverter models can run at slower RPMs to generate the power that is necessary, thus reducing the noise of the engine and making it more fuel-efficient. Inverter generators are best to power sensitive electronic devices such as computers and lights
that use a ballast."
A conventional generator
skips the rectification and inverter stages described above and puts out 120VAC more or less directly from its windings and must run at a certain rpm to produce 60Hz.
Likewise, an automotive alternator initially produces AC at varying frequencies and that is rectified to produce DC -- They are came into standard use in the '60s as the solid state components for rectification became available.
The Cadillac alternator mentioned likely gets the AC directly from the alternator, before rectification, but was probably unable to run a shaver or anything else with a motor because of the frequency problem unless the engine was held to a constant rpm that would allow the alternator to produce 60Hz (aka 60 cycle back then).
BTW, the low noise levels associated with the various small inverter-based generators comes from at least three things:
1. Only runs at rpm required for load
2. Internal parts designed to operate quietly
3. Enclosure and muffling designed for quiet
The inexpensive open-frame conventional generator sets can be after-market modified for #3 above, but not #1 or #2, so they remain relatively noisy. #1, esp with eco-mode IBGs, also results in less fuel consumption.
BTW, if one connects an inverter to a tow vehicle electrical
system, one has then created an IBG! Alternator>rectifier>inverter... If one taps into the alternator output before the rectification stage (the diodes), one has a conventional generator.