Energy economizing AC power system

Claim 1

An energy economizing AC power control system for energizing an induction motor, comprising an AC induction motor having a stator winding, a sine wave power source, solid state power switching means disposed between said power source and said motor for energizing said motor, means coupled to said sine wave power source for generating a train of sawtooth shaped signals at a repetition rate which is twice the frequence of said power source, a substantially nonconductive field effect transistor having a gate electrode, means coupling said train of sawtooth shaped signals to said gate electrode, biasing means for applying a DC bias potential to said gate electrode, said field effect transistor being rendered conductive during the rising excursion of each of said sawtooth signals at a time subsequent to the commencement of each said rising excursion which is jointly dependent on the instantaneous potential of said rising excursion and the magnitude of said DC bias potential, said biasing means including means responsive to changes in the magnitude of current flowing through said motor stator winding resulting from changes in the load on said motor for varying the magnitude of said DC bias potential, and means responsive to the conduction of said field effect transistor for rendering said solid state power switching means conductive to energize said motor for a time interval during the occurrence of each of said sawtooth shaped signals which is a function of the load on said motor, said field effect transistor including a drain electrode which is connected to a capacitor through the primary winding of a transformer, a DC power supply coupled to said capacitor, said capacitor being charged from said DC power supply when said field effect transistor is nonconductive and being discharged through said field effect transistor via said transformer primary winding each time said field effect transistor is rendered conductive, each discharge of said capacitory being operative to generate a pulse in a secondary winding of said transformer, and control means responsive to occurrence of each said pulse in said transformer secondary winding for rendering said solid state power switching means conductive to energize said motor.