A system for modulating a frequency output of a generator coupled to an electric distribution network is described herein. The system includes: a doubly-fed induction generator coupled to a power source selected from at least one of hydropower and fuel combustion, the generator providing an electrical power output having a first frequency based on a rotational speed of the generator; a controller for selecting the rotational speed of the generator; and a converter coupled to the generator for changing the frequency of the output to a selected value, in response to selecting the rotational speed. Methods for modulating a frequency output of a generator coupled to an electric distribution network are also described.