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US 4,266,177 AGranted
Power factor control system for AC induction motors
AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorFrank J. Nola
Life of this patent
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Abstract
A power control circuit for an induction motor wherein a servo loop is used to control power input by controlling the power factor of motor operation, and wherein the power factor is measured by summing the voltage and current derived square wave signals.
Claims9
A power factor control system for an AC induction motor comprising:
- current sampling means including means adapted to be placed in circuit with a winding of a said motor for providing a rectangular output signal timed to turn on responsive to detected current flow through said winding;
- voltage sampling means adapted to sense the voltage of an electrical input applied to said winding and for providing a rectangular wave output signal timed to change with changes in polarity of said voltage across said winding;
- summing means for adding the current and voltage rectangular wave output signals and providing a pulse output of constant height and having a duration proportional to the phase difference of current and voltage;
- a power factor command signal;
- difference means for subtracting said command signal from an averaged amplitude of said pulse output of said summing means and providing a difference signal;
- and
- control means, including a signal responsive switch electrically connected in series with a said winding of said motor, and responsive to said difference signal for varying the duration of "on" time of said switch during each cycle of input power to a said winding as a direct function of load on said motor.
4 more elements
Dependencies are inferred from the claim text.