Electromagnetic induction machines having regulated polar magnetic symmetry

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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 ac voltage and the ac 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 ac 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 h 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 ac 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, protruding from a return magnetic