"EET Science for Motors"

Briefly stated, EET based products reduce a variety of costs associated with the operation of electric motors. Like a supervisor standing at each electric motor, EET Power Managers maintain highest efficiency by ‘managing' a motor and the wiring that feeds the electric power used by the motor.

Whether supervising a home appliance or an industrial machine motor, EET Power Managers:

Saves Machinery by giving just enough current to gently accelerate a motor to full speed when first tuned on. This "soft-start" eliminates damaging shock to the motor and machines when started, extending the life of the equipment.

Protects the System by constantly looking for an electrical /mechanical fault (that can damage a motor), or problems with power lines feeding it, or whatever type equipment the motor drives.

Lower Service Cost by identifying where and when Preventative Maintenance of mechanical systems will be cost effective.

Save Energy by providing just enough electric power for work the motor has to do at any moment; if motors never get more power than they need, they cannot waste it.

"Background of the Invention" ... from US Patent# 4,190,793

BACKGROUND OF THE INVENTION

Conventional induction motors maintain the full sine wave of voltage across the stator winding regardless of the load in the motor. In those cases where the load varies within wide limits, e.g., when the motor is used for hoisting operations, most of the time the motor is not expending its full rated load. In such cases, the iron losses in the stator are substantially the same when the motor is operating below full rated load as is the case when the motor is operating at full rated load; and, due to the low power factor in such cases, the stator current is high and the copper losses are also substantial.

When a conventional induction motor is operating below its full rated load, a fraction of the sine wave of voltage would satisfy the actual load requirement imposed in the motor. Such cutting in part of the sine wave voltage would result in considerably less iron and copper losses and less heating of the stator. The resultant lower operating temperature further reduces the copper losses in the motor due to lowered ohmic resistance. These factors combine to effect a significant reduction in the energy which is consumed by the induction motor, with a consequent conservation in available energy sources and a reduction in motor operating costs.

The present invention is based upon a recognition of the foregoing factors, and provides a simple yet reliable mechanism operative to cause the electrical energy supplied to the stator and the stator flux density of a standard-unmodified-AC induction motor to become a function of its load demand at any given moment. The invention accomplishes this by permitting a greater or smaller portion of the sine wave of voltage from a power source to enter the stator as a function of the percentage of slip of the motor. In other words, the sine wave of the voltage supplied to the motor's stator is modified to suit existing load conditions. This results in the reduction of iron and copper losses.

SUMMARY OF THE INVENTION

In accordance with the present invention, a standard AC induction motor has its stator winding energized from a sine wave power source through wave modifier means operative to vary the portion of each cycle of said sine wave which is coupled from the source to the stator winding, under the control of a control signal which is provided by load detecting means coupled to the rotor of the motor and operating as part of a conditionally operative nonlinear closed loop positive feedback means to produce a control signal which varies with variations in the load on the motor at motor speeds above 95% of synchronous speed.

The load detecting means may comprise a comparatively small AC generator which is coupled to the motor rotor to produce an AC signal that is frequency modulated by variations in the load on the motor, and said frequency modulation is converted to amplitude variations of a DC control signal which controls the wave modifier means. Demodulation and conversion of modulated frequency variations to DC control signal variations may be accomplished by a frequency discriminator circuit whose output is coupled to a signal biased DC amplifier operative at a particular energy-efficient motor speed above 95% of synchronous speed, which functions to reduce the magnitude of the resultant DC control signal when the AC frequency of the generator increases (indicative of decreased motor slip), and which functions to increase the magnitude of the DC control signal when the AC frequency supplied by the generator decreases (indicative of increased motor slip).

The wave modifier preferably includes a normally inoperative pulse generator, such as a multivibrator, that is rendered operative to produce a train of pulses during all or a portion of each cycle from the sine wave energization source. The time duration during which the pulse generator is operative to produce output pulses is controlled by the aforementioned DC control signal and accordingly, it is dependent upon the load on and speed of the motor. The pulse train, when generated, controls the closure of a full wave solid state power switch, such as a Triac, disposed between the sine wave power source and the motor stator, so that the portion of each sine wave which is coupled to the motor stator, and accordingly the field density of the stator winding, varies with variations in the load on the motor.

Click to view "Introduction to Energy Economizer Technology for Induction Motors"  Doc# E82-27-9