Apparatus and method for controlling the output frequency of a wind-driven alternator

An electrical alternator, comprising:

• a stator having a polyphase electrically conductive stator winding disposed thereon;
• a rotor rotatably mounted with respect to said stator, said rotor having a polyphase electrically conductive rotor winding disposed thereon;
• means for measuring the rotational speed of said rotor and for generating a first electrical signal indicative thereof;
• means for generating a second electrical signal representing a desired rotor speed corresponding to a desired output frequency of said alternator;
• means for comparing said first and second electrical signals and for generating a third electrical signal when actual rotor speed is greater than the desired rotor speed and for generating a fourth electrical signal when actual rotor speed is less than the desired rotor speed;
• and,
• control means responsive to said third electrical signal for enabling selected portions of said stator winding, thereby increasing the strength of the stator magnetic field to decrease the rotational speed of the rotor, said control means being responsive to said fourth electrical signal for disabling selected portions of said stator winding, thereby decreasing the strength of the stator magnetic field to increase the rotational speed of the rotor, so that the rotational speed of the rotor is maintained at substantially the desired rotational speed for substantially constant frequency output.

A method of controlling the output frequency of an electrical alternator, said alternator having a stator and a rotor rotatably mounted with respect to said stator, said stator and said rotor having respective polyphase electrically conductive windings disposed thereon, said method comprising the steps of:

• measuring the rotational speed of said rotor and generating a first electrical signal indicative thereof;
• generating a second electrical signal representing a desired rotational speed of said rotor corresponding to a desired output frequency of said alternator;
• comparing said first and second electrical signals and generating a third electrical signal when the amplitude of said first electrical signal is greater than the amplitude of said second electrical signal and generating a fourth electrical signal when the amplitude of said second electrical signal is greater than the amplitude of said first electrical signal, the respective amplitudes of said third and fourth electrical signals being proportional to the amplitude difference between said first and second electrical signals;
• selectively enabling selected portions of said stator winding in response to said third electrical signals, thereby increasing the strength of the stator magnetic field to decrease the rotational speed of the rotor;
• and,
• selectively disabling selected portions of said stator winding in response to said fourth electrical signal, thereby decreasing the strength of the stator magnetic field to increase the rotational speed of the rotor, so that the rotor speed is maintained at substantially the desired speed for substantially constant frequency output.