A system and device for providing AC signal. The system includes: an AC generator that outputs an AC output signal and includes an AC rotor that communicates with a shaft that is rotated at a rotation speed; a speed sensor for sensing the rotation speed; and a controller for controlling a magnetic field of the AC generator in response to the rotation speed; wherein the controller comprises a Field Exciter for providing a current to the AC generator so as to control the magnetic field of the AC generator.