ac or dc, all moped regulators are simple shunts. excess voltage is burned off as heat. a series regulator wont work because it wastes power at idle. a shunt is off at idle. series regulators now have use as led drivers. its called an emitter follower regulator.

moped regulators use scr technology. this means you can configure the half wave dc rectifier/regulator in an ac only mode. you skip the rectifier by not using it.