US 4,806,838 A · A.C. induction motor energy conserving power control method and apparatus

Abstract

Electric power consumed by an a.c. induction motor is measured and sensed changes in power factor are used to modulate the combined magnetic flux produced in the motor field by two sets of RUN windings. A main RUN winding set, which normally couples fully with the a.c. power, is engineered to have sufficient ampere-turns to produce just enough magnetic flux to operate the motor with a light load and maintain a moderately high power factor. Motor driven load increases are determined by sensing a corresponding increase in the power factor of the main RUN winding set, whereupon power flow to a secondary RUN winding is proportionately increased. Considerable energy savings occurs when the motor drives a fluctuating load due to reduced magnetic field excitation under all but full load conditions, with the result that energy ordinarily wasted by eddy currents, copper losses, and poor power factor operation is considerably lessened. Other possible losses due to harmonic distortion of the a.c. power waveform brought about by the phase-delayed thyristor control of the second run winding power are mostly swamped out and masked by the parallel, always-on major power draw by the main run winding. A motor speed-sensitive switch or relay may divert current around the thyristor and fully excite the second run winding during motor start-up, thereby producing full available motor torque during start-up while negating any electrical stress on the control thyristor.

Claims20

Dependent claims

Power control method for use with an electric induction motor,

comprising the steps of:
providing a source of alternating current electric power;
providing the motor with plural RUN winding means;
coupling a first RUN winding means with the source;
variably coupling a second RUN winding means with the source;
sensing reactive power factor of the electric power drawn from the source by the RUN winding means;
increasing the variable coupling when an increase in the power factor is sensed;
and,
decreasing the variable coupling when a decrease in the power factor is sensed.

6 more elements

Power control apparatus for use with an electric induction motor, comprising:

source of alternating current electric power;
induction motor means including at least a first RUN winding means and a second RUN winding means effective for producing motor field excitation;
means for coupling an inconstant load means with said motor means;
means for coupling the first RUN winding means with the electric power source;
means for producing variable a.c. electric power coupling between the source and the second RUN winding means;
means for sensing power factor;
and,
means coupled with said power factor sensing means and said variable a.c. electric power coupling means, effective to produce a controlled increase in the coupling of a.c. power between the source and the second RUN winding means whenever an increase in power factor is sensed;
and to produce a controlled decrease in the coupling of a.c. power between the source and the second RUN winding means whenever a decrease in power factor is sensed.

6 more elements

Induction motor power control means comprising:

alternating current power source;
induction motor means including:
means for producing a first electromagnetic field;
means for producing a second electromagnetic field;
means for combining said electromagnetic fields;
means providing a rotatable output member;
means coupling said combined fields with said member and effective to produce rotation of said member;
means for coupling an inconstant load means with the output member;
means for coupling said first electromagnetic field producing means with said power source;
means for variably coupling said second electromagnetic field producing means with said power source;
means for sensing phase lag of the a.c. power flow between the electromagnetic field producing means and the power source relative with instant voltage phase of the power source;
and,
means for determining a controlled increase in the efficacy of the variable coupling when the sensed phase lag decreases, and for determining a controlled decrease in the efficacy of the variable coupling when the sensed phase lag increases.

10 more elements

Dependencies are inferred from the claim text.

A.C. induction motor energy conserving power control method and apparatus

Life of this patent

A.C. induction motor energy conserving power control method and apparatus

Life of this patent

Abstract

Claims20