Trumpy,
You are correct for the standard generator.
A an inverter generator can use a DC generator (see
http://micro.magnet.fsu.edu/electromag/java/generator/dc.html ) or an unregulated AC generator with a full bridge rectifier (half bridge does not make economical sense as you would only get half the available power out). This output is then inverted to AC using a timer for the frequency (same as a stand alone solar inverter).
Yamaha, Kawasaki (I think), and Honda (if they still manufacture there own generators) should have one. I have not looked for one above about 10KVA so I don't know if large ones exist. It seems unlikely as a DC generator, but maybe as the dual conversion AC style. I don't often find myself above the 30KVA size where I am looking at standard generators.
An advantage to these styles is that they can be easily paralleled. One serving as the master providing the frequency for the others to follow.
