Might be a PLL locked by the mains.
An independent frequency generator is too much expensive.
Some of them have a tachometer to control rotation speed.

J.B. Wood a écrit le 20/03/2019 Ã* 11:57Â*:
Hello, all.Â* This isn't a repair question but, not having seen any
circuit schematics, I've been wondering what circuitry constitutes the
time base (what governs the 60 Hz AC output freq) in consumer inverter
generators (e.g. the Honda EU series)?Â* Is it crystal-controlled or
something else? I'm assuming it depends on the inverter portion
itself, not the rpm of the engine.Â* Since these appliances are
designed to function in a variety of temperature/humidity environments
I would think frequency stability is important.Â* Thanks for your time
and comment. Sincerely,