Energy economizer for polyphase induction motors

An energy economizing AC power control system operative to reduce the iron and copper losses in a conventional three phase AC induction motor by varying the form and magnitude of input voltage coupled thereto, comprising a conventional three phase AC induction motor having three stator windings and a rotor adapted to be coupled to a load, a three conductor three phase sine wave power source for energizing said stator windings to effect rotation of said rotor, and a conditionally closed loop positive feedback control means that becomes operative to control the energization of said stator windings from said power source by reference to a particular speed caused to be energy-efficient by properties inherent to induction motors during a limited range of motor speeds near the full speed of said motor, said closed loop positive feedback control means comprising:

• motor load detecting means coupled to said rotor and operative to produce a frequency modulated signal related to the load on said motor, frequency discriminator means coupled to said load detecting means for producing a DC control voltage which varies in magnitude in inverse relation to the speed of said motor, emitter-follower means coupled to the output of said frequency discriminator means to render said frequency discriminator means insensitive to variations of subsequent circuit means while coupling said DC control voltage to said subsequent circuit means, a plurality of voltage coupling means coupled to the output of said emitter-follower means for providing a plurality of DC control voltage outputs which are isolated from each other, two wave modifier means responsive respectively to said DC control voltage outputs and including associated switching means disposed between two conductors of said three phase power source and two of said three stator windings, the third stator winding being directly connected to the third conductor of said power source, said wave modifier means being operative to apply full sine waves of voltage from said power source to their associated stator windings during rotational start-up and speed build-up of said motor and, as said motor reaches said particular speed, then being operative to substantially maintain said particular speed by varying the electrical angle of each cycle of said power source which is actually coupled to said two stator windings, and therefore to said third stator winding, thereby providing varying fractions of each sine wave of voltage from said power source to all three of said stator windings in accordance with the energy requirements imposed on said motor by the rotor load at any given moment and in accordance with the inherent electromechanical properties of said motor, whereby said closed loop positive feedback control means functions to substantially reduce the iron and copper losses of said conventional motor by causing the average current supplied from said power source to said stator windings to be supplied primarily as a function of the load on and properties inherent to said motor as the load of said motor varies between zero and maximum rated load.