Seems I'm showing my age again.
AC field eh! isn't time a b*&"h seems only yesterday watching a pal try and
prove that a series genset won't generate if you short the output.
Oh well time marches on ... as for brushless systems some Kango sets circa
1970's tried this by using an offset field biased with a capacitor and a
squirrel cage type armature IIR.
Sorry I can't be of further help as obviously my obsolete training and
experience is no longer the "Usual" but one thing that will not change is
that a generator makes electricity by moving a conductor across a magnetic
field,so good luck in your endeavours.

CJ