Single and polyphase electromagnetic induction machines having regulated polar magnetic symmetry

What is claimed is:

1. An electromagnetic induction machine comprising:

a rotatable, magnetically excitable rotor;

a stationary stator operatively associated with said rotor;

at least two windings electrically connected in series and each winding defining a pair of magnetic poles disposed proximate said rotor in said stator; and

capacitor means in parallel combination with one of said windings and said combination in series with the other one of said windings, the size of the capacitor being such that a quasi-parallel resonant circuit is formed with said one winding and a quasi-series resonant circuit is formed with said other one of said windings.

2. An induction machine as claimed in claim 1, wherein said machine has at least one pair of power input terminals which are adapted to be coupled to an a.c. power source and the serially connected windings are coupled across said input terminals.

3. An induction machine as claimed in claim 2, wherein said rotor includes a plurality of longitudinally insulated conductors, said stator circumferentially surrounds said rotor and includes teeth radially extending towards said rotor, and said windings establish said magnetic poles via said teeth when excited, wherein a balanced rotating magnetic field is present due to the transfer of energy from the excited windings to said rotor, the return of energy from said rotor to said windings and the storage of the returned energy in said capacitor.

4. An electromagnetic induction machine as claimed in claim 1, wherein said rotor circumferentially surrounds said stationary stator.

5. An electromagnetic induction machine as claimed in claim 1, wherein said capacitor means comprises at least one alternating-current bipolar, non-electrolytic liquid-type capacitor.

6. An electromagnetic induction machine as claimed in claim 1, further comprising a second capacitor means arranged in series with a switch means, said arrangement being in parallel with said capacitor means, said switch means being normally closed, and opened when said rotor reaches a certain speed.

7. An electromagnetic induction machine as claimed in claim 6, wherein said second capacitor means being selected from the group consisting essentially of a.c. bipolar, non-electrolytic liquid-type capacitors and a.c. bipolar electrolytic-type capacitors.

8. An electromagnetic induction machine as claimed in claim 2, wherein said capacitor means in said two quasi-resonant circuits serve as a phase doubling capacitor by creating two balanced phases from said input power source.

9. An electromagnetic induction machine as claimed in claim 1, wherein the phase voltages generated for each of said two windings is approximately equal to the applied phase voltage divided by the square root of two.

10. An electromagnetic induction machine as claimed in claim 1, wherein said serially connected windings are wound with effective turns ranging from the same number of turns in each winding to a ratio of 1.05:1.

11. An electromagnetic induction machine as claimed in claim 1, wherein said serially connected windings substantially are wound with wire size ranging from the same size in each winding to a ratio of 1:2.

12. An electromagnetic induction machine as claimed in claim 11, wherein the serially connected windings, when wound with unequal wire sizes, having the quasi-series winding as the winding with the smaller circular mil area and the quasi-parallel winding as the winding with the larger circular mil area.

13. An electromagnetic induction machine as claimed in claim 1, further comprising an air gap between said teeth and said rotor, wherein said air gap includes a perfectly round revolving magnetic field.

14. An electromagnetic induction machine as claimed in claim 1, wherein due to the reduction of current in the windings, said machine is operative in the linear portion of the BH curve below saturation.

15. An electromagnetic induction machine as claimed in claim 1, wherein the quasi-resonant windings are placed relative to each other in the range between 60 and 130 electrical degrees.

16. An electromagnetic induction machine as claimed in claim 15, wherein the quasi-resonant windings are placed at substantially 90 electrical degrees relative to each other.

17. An inductive dynamoelectric machine comprising:

a hollow, cylindrically shaped, longitudinally slotted stator;

at least a pair of stator windings disposed in the slots around the interior of said stator, said stator windings being electrically serially connected together and connected across a power input of said dynamoelectric machine;

a capacitor in parallel combination with one of said stator windings and said combination in series with the other said stator winding forming a quasi-double-resonant circuit that includes a quasi-series resonant circuit and a quasi-parallel resonant circuit;

a longitudinally slotted, rotatable rotor disposed in the interior space defined by said stator; and

a plurality of electrically coupled rotor windings disposed in the slots on the periphery of said rotor wherein said stator windings and said rotor windings are magnetically coupled together and a balanced rotating magnetic flux wave is produced due to the storage and delivery of energy by the capacitor, the stator windings and the rotor windings under substantially all load conditions.

18. An inductive dynamoelectric machine as claimed in claim 17, wherein the capacitance value of said capacitor is selected to produce said quasi-double-resonance circuit and wherein the Q factor of said quasi-double-resonance circuit is continually adjusted by the admittance of the rotor windings.

19. An electromagnetic induction machine as claimed in claim 17, wherein said capacitor means comprises at least one alternating-current bipolar, non-electrolytic liquid-type capacitor.

20. An electromagnetic induction machine as claimed in claim 17, further comprising second capacitor means arranged in series with a switch means, said arrangement being in parallel with said capacitor means, said switch means being normally closed, and opened when said rotor reaches a certain speed.

21. An electromagnetic induction machine as claimed in claim 20, wherein all second capacitor means being selected from the group consisting essentially of a.c. bipolar, non-electrolytic liquid-type and a.c. bipolar, electrolytic-type capacitor.

22. An electromagnetic induction machine as claimed in claim 17, wherein said capacitor means in said two quasi-resonant circuits serve as a phase doubling capacitor by creating two balanced phases from said input power source.

23. An electromagnetic induction machine as claimed in claim 17, wherein the phase voltages generated for each of said windings are approximately equal to the applied phase voltage divided by the square root of two.

24. An electromagnetic induction machine as claimed in claim 17, wherein said serially connected windings are wound with effective turns ranging from the same number of turns in each winding to a ratio of 1.05:1.

25. An electromagnetic induction machine as claimed in claim 17, wherein said serially connected windings substantially are wound with wire size ranging from the same size in each winding to a ratio of 1:2.

26. An electromagnetic induction machine as claimed in claim 17, wherein the serially connected windings, when wound with unequal wire size, have the quasi-series winding as the winding with the smaller circular mil area and the quasi-parallel winding as the winding with the largest circular mil area.

27. An electromagnetic induction machine as claimed in claim 17, further comprising an air gap between said teeth and said rotor, wherein said air gap includes a perfectly round revolving magnetic field.

28. An electromagnetic induction machine as claimed in claim 17, wherein due to the reduction of current in the windings, said machine is operative in the linear portion of the BH curve or well below saturation.

29. An electromagnetic induction machine as claimed in claim 17, wherein the quasi-resonant windings are placed relative to each other in the range between 60 and 130 electrical degrees.

30. An electromagnetic induction machine as claimed in claim 29, wherein the quasi-resonant windings are placed at substantially 90 electrical degrees relative to each other.

31. A polyphase inductive dynamoelectric machine adapted to be supplied with a polyphase power at a like number of power phase input terminals comprising:

a rotatable rotor carrying a plurality of interconnected rotor windings;

a stator circumferentially surrounding said rotor;

a pair of serially connected stator windings for each phase of said polyphase power disposed in said stator, each pair receiving, via one of said power input terminals, a different phase of said polyphase power and adapted to be magnetically coupled to said rotor windings; and

a respective capacitor for each pair of stator windings, said respective capacitor connected in series with a first winding of said pair and in parallel with a second winding thereof, the size of the capacitor being such that a respective quasi-series resonant circuit is formed with said first winding and a respective quasi-parallel resonant circuit is formed with said second winding.

32. A polyphase inductive dynamoelectric machine as claimed in claim 31, wherein all the pairs of stator windings are connected in a .DELTA. configuration with respect to said input terminals.

33. A polyphase inductive dynamoelectric machine as claimed in claim 31, wherein all the pairs of stator windings are connected in a wye configuration with respect to said input terminals.

34. A method of generating torque form an a.c. power source including the steps of:

forming a quasi-souble-resonant circuit comprising two stationary serially connected inductive elements and a capacitive element connected in parallel combination with one of said inductive elements and the combination connected in series with the other of said inductive elements to respectively form a quasi-parallel resonant circuit and a quasi-series resonant circuit;

providing a rotatable inductive element adapted to deliver torque;

applying said a.c. power across said two serially connected inductive elements;

magnetically coupling said two serially connected inductive elements with said rotatable inductive element; and

producing a balanced rotating magnetic flux wave by storing and by delivering stored energy from one of said quasi-serial resonant circuit or said quasi-parallel resonant circuit to the other one of said quasi-serial resonant circuit or said quasi-parallel resonant circuit upon a change in the magnetic flux linking said two inductive elements and said rotating inductive element.

35. A method of generating torque from an a.c. power source including the steps of:

forming a quasi-double-resonant circuit comprising two stationary serially connected inductive elements and a capacitive element connected in series with one of said inductive elements and in parallel to the other of said inductive elements to respectively form a quasi-series resonant circuit and a quasi-parallel resonant circuit;

providing a rotatable inductive element adapted to deliver torque;

applying said a.c. power across said two serially connected inductive elements;

magnetically coupling said two serially connected inductive elements with said rotatable inductive element; and

producing a balanced rotating magnetic flux wave by storing and by delivering stored energy from one of said quasi-serial resonant circuit or said quasi-parallel resonant circuit to the other one of said quasi-serial resonant circuit or said quasi-parallel resonant circuit upon a change in the magnetic flux linking said two inductive elements and said rotating inductive element.

36. A polyphase inductive dynamoelectric machine adapted to be supplied with a polyphase power at a like number of power phase input terminals comprising:

a rotatable rotor carrying a plurality of interconnected rotor windings;

said rotor circumferentially surrounding a stationary stator;

a pair of serially connected stator windings for each phase of said polyphase power disposed in said stator, each pair receiving, via one of said power input terminals, a different phase of said polyphase power and adapted to be magnetically coupled to said rotor windings; and

a respective capacitor for each pair of stator windings, said respective capacitor connected in quasiseries with a first winding of said pair and in parallel with a second winding thereof, the size of the capacitor being such that a respective quasi-series resonant circuit is formed with said first winding and a respective quasi-parallel resonant circuit is formed with said second winding.

37. A polyphase inductive dynamoelectric machine as claimed in claim 36 wherein all the pairs of stator windings are connected in a .DELTA. configuration with respect to said, input terminals.

38. A polyphase inductive dynamoelectric machine as claimed in claim 36, wherein all the pairs of stator windings are connected in a wye configuration with respect to said input terminals.

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FIELD OF THE INVENTION

The present invention relates to single and polyphase electromagnetic induction machines having regulated polar magnetic symmetry.

BACKGROUND OF THE INVENTION

With the advent of higher utility rates, power factor penalties and demand charges, prior art induction motors have many disadvantages. Most induction motors in use are over-sized and inefficient. Consequently power bills are higher than need be due to motor inefficiency, high demand and poor power factor (KW/KVA). As is known, the power factor involves the phase relationship between the a.c. voltage and the a.c. current. Utility companies generally charge a premium to the user when the power factor falls below 0.85 (a power factor of unity is present when the voltage and current are of the same waveform completely in phase).

When energy rates were low, these drawbacks were not as important as they now are. Often demand (the total electrical power that needs to be available, but not necessarily used from the line) and power factor penalties are as much or more than the basic energy charge.

The most efficient prior art, single-phase induction motors are of the permanent-split capacitor design, but they have low torque characteristics and are efficient only when the magnetic field of the direct phase winding is balanced with that of the auxiliary phase winding and their respective currents are displaced by 90.degree.. In most split capacitor motors, a large stator winding is directly connected to the power terminals and a smaller auxiliary winding, serially connected to a capacitor, is also connected across the input. The 90.degree. displacement of current between both stator windings only exists at design load; at other load points a disproportionate distribution of magnetic flux exists which sets up negative sequence currents in the rotor and stator, space harmonics in the air gap (e.g., the degree to which the flux distribution in the air gap is not sinusoidal) and high leakage reactance from the stator end turns. For example, an imbalance of phase voltages on the order of 3% can cause a 15% to 20% increase in motor losses.

This condition is not restricted to single-phase motors but is also prevalent in polyphase motors when an imbalance occurs in the polyphase voltage supply. These losses in both single and polyphase motors can degrade insulation and reduce bearing life due to overheating of the rotor and, in addition to overheating, an imbalance creates higher magnetostriction noise and poor operating performance, as can be seen in Table 1.

Another significant disadvantage is in the manufacture of new motors. Engineers are now focusing on design tolerances in an attempt to increase motor efficiencies, producing a motor which is more susceptible to failure due to environmental changes and bearing wear. Attempts have been made to create a balanced condition by a series resonating winding in combination with a phase winding but this is a tuned condition for a narrow spectrum only, and at certain load points circulating harmonic currents increase, and the efficiency is reduced to below that of the standard design.

Induction motors and generators are efficient only when properly sized to the load and when the line voltage is balanced. When operated below design load or with a system imbalance, a disproportionate polar magnetic condition exists which sets up negative sequence currents in the rotor and stator, space harmonics in the air gap and high leakage reactance due to high currents in the phase winding. Again, an imbalance in the order of 3% can cause a 15% to 20% increase in motor or generator losses. This reduces insulation and bearing life and creates an imbalance which is manifested as higher magnetostriction noise and poor operating performance. Attempts have also been made to create a balanced and controlled condition in the motor by a series resonating winding in combination with a phase winding but this is a tuned condition for a narrow spectrum and at certain load points circulating harmonic currents increase and the efficiency is reduced to below that of the standard design.

SUMMARY OF THE INVENTION

The single-phase, dynamoelectric machine, which can be a motor or a generator, includes a rotatable rotor usually in the interior space defined by a hollow cylindrical stationary stator. Both the rotor and stator have slots therein facing each other within which are disposed windings. The rotor windings may be connected at each end to form a squirrel cage or brought out via slip rings. In the stator, two windings are electrically connected in series and are circumferentially placed around the interior surface of the hollow stator core to form magnetic poles. A capacitor is coupled in parallel with one winding and this combination is connected in series with the second winding. The size of the capacitor is such that a quasi-series resonant circuit is formed with the second winding and a quasi-parallel resonant circuit is formed with the first winding. The serially connected stator windings are connected across the single-phase or polyphase power input terminals.

When power is applied to the motor, a balanced rotating magnetic field is generated wherein the Q factor of the circuit is continually adjusted by the admittance of the rotor windings. Because of the interaction between the quasi-series resonant circuit and the quasi-parallel resonant circuit, unused energy delivered to the rotor in the form of magnetic flux is returned via one of the stator windings and, upon collapse of the magnetic field, the resulting voltage is stored in the capacitor. This is due to, for example, a reduction in load torque on the rotor. In another sense, when the torque requirements on the rotor are higher, the capacitor delivers stored energy to the appropriate winding to compensate for the additional power requirements and maintain a balanced distribution of magnetic flux circumferentially rotating around the rotor.

The method of generating torque from an a.c. power source includes the step of forming a quasi-double-resonant circuit, including a capacitive element which is connected in parallel to one of the inductive elements and this combination connected in series with the other inductive element, providing a rotatable inductive element adapted to deliver torque; applying power across the two serially connected, stationary inductive elements, magnetically coupling all the inductive elements and producing a balanced rotating magnetic flux wave via the mechanism described above with respect to the quasi-serial and quasi-parallel resonant circuits.

In one embodiment, the polyphase induction motor includes three pairs of serially connected stator windings wherein a capacitor is coupled in parallel to one of the windings in each pair and the combination coupled in series with other winding in the pair to form a quasi-double-resonant circuit. A further embodiment of the polyphase motor includes three primary stator windings which receive, via one of the power input terminals, a different phase of the three-phase power applied to the motor. Three secondary stator windings are circumferentially interleaved in the stator between the three primary stator windings and are magnetically coupled to the primary windings but are not directly connected to the power input terminals of the motor. A capacitor is provided for each pair of secondary stator windings and the respective capacitor is in parallel with at least one secondary stator winding. Each capacitor is sized to form a quasi-parallel floating resonant circuit with the parallel connected secondary stator winding.

Thus, it is a primary object of the present invention to eliminate or control space harmonics in the air gap, negative sequence currents in the rotor and stator windings and increase the efficiency of an induction motor or generator.

It is another object of the present invention to increase the torque rating of a motor without increasing hysteresis loss due to magnetic saturation.

It is a further object of the present invention to improve the power factor of an induction motor.

It is an additional object of the present invention to store unused energy returned to the stator windings and deliver stored energy to the magnetic circuit upon demand.

It is still another object of the present invention to produce a balanced rotating magnetic flux wave around the rotor at substantially all loads.

The subject matter which is regarded as the invention together with further objects and advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical representation of a single-phase motor with regulated magnetic polar symmetry.

FIG. 2 is an electrical schematic diagram of the single-phase motor of FIG. 1, but the circuit does not include representations of the stator core material or the rotor material.

FIG. 3A is an oscilloscope trace of the voltage waveforms associated with each of the stator windings (and the capacitor) when the oscilloscope is set to trigger on the positive going slope of the supply line voltage.

FIG. 3B is an oscilloscope trace of the current waveforms associated with each of the stator windings and the capacitor when the scope is also set to trigger on the positive going slope of the supply line voltage.

FIG. 4A is an oscilloscope trace of the line supply voltage V.sub.L and the line current I.sub.L at approximately full load for a 1/4 horsepower motor supplied with 120 volts a.c.

FIG. 4B is an oscilloscope trace of the line supply voltage and the line current at approximately half-load.

FIG. 4C is an oscilloscope trace of the line supply voltage and the line current at no-load.

FIG. 5 is a time-lapse illustration of an oscilloscope trace of the line supply voltage and line current over the entire load range of the motor.

FIG. 6 is a graphic representation of the rotor current versus slip speed in the induction motor of FIG. 1.

FIG. 7A shows the effect of resistance on the shape of a series resonance curve.

FIG. 7B shows the effect of L/C ratio on the shape of a series resonance curve.

FIG. 7C shows the parallel resonance curve.

FIG. 8 is a diagrammatical representation of a polyphase induction motor with regulated polar magnetic symmetry including a quasi-double-resonant equalizer circuit.

FIG. 9 is an electrical schematic diagram of the polyphase, quasi-double-resonant induction motor of FIG. 8 wherein the stator resonant windings are connected in a .DELTA. configuration with respect to the source.

FIG. 10 is an electrical schematic diagram of the polyphase, quasi-double-resonant induction motor of FIG. 8 wherein the stator resonant windings are connected in wye configuration with respect to the source.

FIGS. 11A through 11L are diagrams showing the electric current and magnetic conditions in a two-pole, three-phase induction motor for each 30.degree. of a complete cycle.

FIG. 12A is an oscilloscope trace of the line supply voltage V.sub.L and the line current I.sub.L of one phase at full load in a 40 horsepower, three-phase, quasi-double-resonant induction motor.

FIG. 12B is an oscilloscope trace of the line supply voltage and the line current of one phase at 75% load for the motor of FIG. 12A.

FIG. 13 is a switching network for changing rotation of the double-resonant polyphase motor of FIG. 8.

FIG. 14A is a diagrammatical representation of a polyphase induction motor with regulated magnetic symmetry with a parallel floating quasi-resonant circuit. The primary stator windings are connected in a wye configuration to the source, its parallel, floating windings are connected in a wye configuration, and the capacitors in the floating circuit are connected in a .DELTA. configuration.

FIG. 14B is an electrical representation of a polyphase induction motor with regulated polar magnetic symmetry including a parallel floating quasi-resonant circuit with its primary stator windings connected in a wye configuration to the source, its parallel floating winding are in a wye configuration and the capacitors in the floating circuits are in a .DELTA. configuration.

FIG. 15 is an electrical diagram of the polyphase, parallel floating quasi-resonant induction motor wherein the primary stator windings are in a wye configuration with respect to the inputs and the parallel floating stator windings and capacitors are in a .DELTA. configuration.

FIG. 16 is an electrical schematic diagram of a polyphase induction motor with regulated polar magnetic symmetry having a floating quasi-parallel resonant design with its primary phase, stator windings connected in a .DELTA. configuration with the source, its parallel floating resonant stator windings connected in a wye configuration and the capacitors in the floating circuits are in a .DELTA. configuration.

FIG. 17 is an electrical schematic diagram of a polyphase, parallel floating induction motor wherein the primary stator windings are in a .DELTA. configuration, the secondary stator or parallel floating windings are in a .DELTA. configuration and the capacitors in the floating circuits are in a wye configuration.

FIG. 18A is an oscilloscope trace of the line supply voltage and the line current of one phase at full load in a 40 horsepower, three-phase, quasi-parallel floating resonant induction motor.

FIG. 18B is an oscilloscope trace of the line supply voltage and the line current of one-phase at 75% load in the quasi-parallel floating resonant induction motor.

FIG. 19 is a phaser diagram of an ideal double-resonant motor with quasi-series resonance at full-load.

FIG. 20 is the phaser diagram of a 1/3 HP motor after conversion to a quasi-double-resonant motor with quasi-series resonance at full-load.

FIG. 21 is a phaser diagram of an ideal double-resonant motor with parallel resonance at no-load.

FIG. 22 is the phaser diagram of a 1/3 HP motor after conversion to a quasi-double-resonant motor with quasi-parallel resonance at no-load.

FIG. 23 is an electrical schematic diagram of a double-resonant motor incorporating the teachings of the present invention and used in conjunction with explaining FIGS. 19 through 22.

FIG. 24 is a representation of the magnetomotive force in the air gap surrounding the circumference of the rotor in a quasi-double-resonant motor. Each wave represents the force (flux) in the air gap over the circumference of the rotor at a given time in one cycle of the input power .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagrammatical representation of a single-phase a.c. induction motor in a squirrel cage rotor configuration. Stator ST.sub.1 is a generally hollow, cylindrically shaped, slotted structure of laminated sheet steel. A rotor RO.sub.1 is rotatably disposed in the interior space of the stator and is of like material. For simplification, the stator is shown as having four polar areas or teeth TA.sub.1, TB.sub.1, TC.sub.1, TD.sub.1, protrud