Patent Application
20110140560
The present invention relates generally to an electrical generator, and more particularly, to an improved induction generator referenced to an AC power source.
Recently, brought on by the shortage in fossil fuel and the ecological consequences of such use, various proposals have been devised for inserting locally generated electrical power into a public utility grid. An assortment of renewable fuel sources have been investigated. The ideal alternative energy fuel source will not have an adverse impact on the ecology and will result in a high grade fuel at a low cost. Common examples of alternative energy fuel sources are wind, hydro, hydrocarbon gas recovery, solar, geothermal and waste heat recovery. Each of these fuel sources may be teamed with electrical power generators.
The difficulty in utilizing these fuel sources lies in the quality of the fuel itself. For example, variations in wind velocity severely limit the usefulness of wind power machines as a steady and constant fuel source for a conventional synchronous or induction generator. This is because conventional generators can deliver usable power only when they operate within a particular speed range. As a result, the wind power machines must employ doubly wound AC generators, or elaborate propeller pitch control and mechanical drive systems that provide appropriate generator speed. To be of practical use, however, doubly-fed systems must provide appropriate rotor excitation and maintain constant stator voltage, which is not easily accomplished. Where high speed geothermal turbines or low speed water wheels are employed, mechanical speed control, reduction, or step-up devices must be used to provide the appropriate rotational speed for AC generation. The efficiency losses which accompany these types of mechanical conversion devices compromise their economic viability and render them generally unsuitable as sources of power.
The compensation provided by these mechanical conversion systems are essential, however, because the insertion of locally generated electrical power into a public utility grid requires exact phase and frequency matching. Accordingly, if a device could be self-synchronizing and tolerant of widely varying rotational speed, the use of alternative fuel sources as a means for generating electricity would be greatly enhanced. One noteworthy example of such a self-synchronizing rotating device can be found in several patents issued to Leo Nickoladze, specifically in U.S. Pat. Nos. 4,701,691 and 4,229,689 which are expressly incorporated herein by reference as though fully set forth.
These latter examples rely on electrical cancellation within the inductive device itself whereby all variations in input power are effectively taken out. An exemplary embodiment of such induction device is shown in
In operation, the exciter rotor 18 is rotated by the local power source 19 within the rotating magnetic field developed by the exciter stator 14. The induced signal frequency at the output of the exciter rotor 18 is equal to the summation of the angular rate of the local power source 19 plus the frequency of the AC power source 16. As the generator rotor 20 is rotated within the generator stator 22, the inverse connection to the exciter rotor 14 causes the angular rate produced by the local power source 19 to be subtracted out. The result being an induced voltage at the output of the generating stator 22 equal in rate to the frequency of the AC power source.
While the foregoing Nickoladze solution provides a theoretical output voltage where only the line frequency of the utility grid is produced, in practice, the manufacture of these devices is often fraught with difficulty for three-phase power applications due proper phase angle alignment between the exciter and generator stages and the windings. Often, due to the physical windings of the rotor and stator elements, phase angle alignment between the exciter and generator stages could not be achieved in the past. Moreover, some devices simply failed to perform altogether because the phase sequence of the windings was improper. These problems become even more pronounced when the exciter stage and generator stage are manufactured independently of one another.
Accordingly, there is a current need for a three-phase line synchronous generator that can be produced with proper phase angle alignment for three-phase power applications resulting in a constant frequency and voltage output at variable shaft speeds. It is desirable that phase angle alignment be easily achieved even for exciter and generator components wound in opposite directions or with phases that start in different slots on the core with relation to the keyway.
An embodiment of the present invention is directed to a method and apparatus that satisfies this need. There is, therefore provided, according to an embodiment of a three-phase line synchronous generator, an exciter stator having n poles, an exciter rotor having n poles and disposed for rotation within the exciter stator, a generator stator having n poles, and a generator rotor having n poles, the generator rotor being mechanically coupled to the exciter rotor and disposed for rotation within the generator stator, wherein the poles of the stators, or the poles of the rotors, are angularly displace by one pole pitch.
An attractive feature of the described embodiments is that the line synchronous generator remains self-synchronizing despite variations in shaft speeds. Moreover, proper phase angle alignment can be readily achieved even for exciter and generator components independently manufactured with windings in opposite directions or with phases that start in different slots on the core with relation to the keyway. This economically viable solution to alternative power sources has a major potential for resolving the present energy shortage with minimum adverse ecological consequences.
It is understood that other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein is shown and described only embodiments of the invention by way of illustration of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:
A preferred embodiment of the present invention is shown in
The generator stage 26 includes a generator rotor 34 connected for common rotation with the exciter rotor 32 inside the interior of a generator stator 38. The generator rotor 34 also includes three electromagnetic pole pairs each wound with a secondary winding. The secondary windings of the generator rotor are inversely connected to the secondary windings of the exciter rotor 32 to effect electrical cancellation of the frequency induced by the angular rotation of the local power source. The generator stator 38 is connected to the AC power source 30.
In an alternative embodiment of the present invention, the rotors of the exciter and generator stages are connected to the AC power source, and the three-phase windings of the exciter and generator stators are connected for electrical cancellation. Turning to
Similarly, the generator stage 64 includes a generator stator 74 with three electromagnetic pole pairs wound with secondary windings. The secondary windings of the exciter stator 72 are inversely connected to the secondary windings of the generator stator 74 to effect electrical cancellation of the frequency induced by the angular rotation of the local power source. The generator rotor 75, connected for common rotation with the exciter rotor 52, is connected to the AC power source 54. For explanatory purposes only, the embodiments of the present invention will be described for a three-phase line synchronous generator configured as stator primary machine, i.e., stators connected to the AC power source. However, it will be understood by those skilled in the art that the present invention is not limited to stator primary machines, and that all described embodiments and test procedures are equally applicable to rotor primary machines, i.e., rotors connected to the AC power source.
As shown in
The operation of the generator is described with reference to
While this theoretical solution resolves the effects of shaft speed variations on the output frequency of a three-phase line synchronous generator, optimal output performance can only be achieved by the proper phasing alignment between the exciter and generator stages 24, 26. This connection is achieved by initially ensuring that the primary windings of the exciter stage has the same phase sequence as the primary windings of the generator stage, and then inversely connecting the secondary windings of the exciter and generator stages.
As a result of exciter and generator stages being manufactured independently of one another, it is important to determine the proper connection between the primaries to ensure the each stage of the line synchronous generator has the same phase sequence. This determination can be made in a number of ways. For example, with a stator primary machine, a small three phase motor may be driven from the stator windings with power applied to the rotor windings. The proper phasing sequence of the stator windings will occur when the motor is driven in the same direction of rotation from both the exciter stator winding and the generator stator winding. Another way to obtain the proper phase sequence is with a phase rotation meter, or with two lamps and an AC capacitor connected in wye in accordance with known test techniques in the art.
Once the proper phase sequence is established, the stator windings are connected to the corresponding phases of the AC power source. The proper phase angle between the rotor windings is then established by the interconnection process. To obtain electrical cancellation of the frequency induced by the angular rate of the rotor shaft, the rotor windings must be connected such that the voltage induced by angular rotation in each exciter rotor winding has an equal but opposite polarity than the voltage induced in the generator rotor winding to which it is connected.
Vector diagrams provide a useful mechanism for illustrating how the interconnections between the second windings can be ascertained. As shown in
T03=0° and T3=180°; A 180°
T01=120° and T1=300°; A 180°; and
T02=240° and T2=60°; A 180°.
The same phase relationships hold true for the secondary connections shown by the vector diagrams in
In contrast, there are six other possible interconnections which will not effect electrical cancellation of the frequency induced by the angular rotation of the rotors. These six incorrect connections are shown by the vector diagrams in
T01=300° and T1=300°; A 0°
T02=60° and T2=60°; A 0°; and
T03=180° and T3=180°; A 0°.
These vector diagrams are also useful for establishing test parameters for determining the proper interconnections between the rotor windings during the manufacturing process. Common to each of vector diagram of
T2 to T02=2 Vm
T3 to T03=2 Vm
T2 to T03=√3 Vm
T3 to T02=√3 Vm
Since vectors have a designated length and direction in space, these results can be verified with an ordinary ruler.
The vector diagrams can be confirmed mathematically. Classic electrical theory holds that when a voltage is applied to a primary winding of an induction generator, a voltage will be induced into the open circuit secondary winding. A wye-connected three-phase winding has each phase displaced by 120°. The induced voltage at the open circuit secondary terminals will be balanced. For the phasing test, a jumper wire interconnects one terminal of each secondary winding. In
T2 to T02
T3 to T03
T2 to T03
T3 to T02
As can readily be seen from
The voltage across T2-T03 is the resultant of an oblique triangle defined by sides T1-1-T03, T01-T2, and T2-T03. When properly aligned, classic three-phase electrical theory identifies the angles as shown on
For Proper Alignment:
The same holds true for the voltage between T3-102. Therefore, with proper alignment, the voltage will be one pair of terminals at two times line voltage and one pair of terminals at \13 times the line voltage.
With the knowledge gleaned from these vector diagrams, a methodology of interconnecting the rotor windings can be ascertained which significantly reduces the manufacturing cost while increasing product yield. Specifically, the method for determining the proper interconnections in a stator primary machine requires the connection of a pair of rotor windings and then finding two remaining pairs of substantially identical voltages between the rotor windings.
Turning to
Either the primary or secondary could be the rotor or stator, but they must be the same part. Thus, if one half of the synchronous generator is configured as a rotor primary machine, then the other half of the synchronous generator must also be configured as a rotor primary machine.
As defined by the vector diagrams of
2(90)=180 volts for one voltage pair; and
√3(90)=156 volts for the other voltage pair.
To perform the test, a jumper wire is placed across a terminal for each rotor winding. In this example, a jumper wire is first placed across T1 and T01 and the following voltages are obtained by test:
T2-T02=156 volts
T2-T03=90 volts
T3-T02=180 volts
T3-T03=156 volts.
These measured voltages are consistent with
The jumper wire is then removed and placed across another terminal pair. In this example, the jumper wire is next placed across T2 and T01, and the following voltage are obtained by test:
T1-T02=156 volts
T1-T03=180 volts
T3-T02=180 volts
T3-T03=156 volts.
This result is consistent with
In rotor primary machines, the exciter and generator rotors are connected to the AC power source and the testing methodology described in connection with
Once the proper phase angle between the secondary windings is established (whether it be the rotor or stator windings), electrical compensation may then be inserted between each pair of the three-phase secondary windings. Specifically, resistors and capacitors can be inserted between the respective secondary windings to expand the dynamic operating range of the device without the necessity of continual phase angle adjustments between the exciter and generator stages.
Turning to
Another important parameter for optimizing performance of the three-phase line synchronous generator is the phase angle between the exciter and generator stages. A 60° phase angle between the exciter and generator stages is needed to achieve a 180° phase shift between each of the secondary windings. This concept can be well illustrated by reference to the vector diagrams of
T1=300° and T01=300°; Δ0°
T2=60° and T02=60°; Δ0°
T3=180° and T03=180°; Δ0°
The following phase angles between the connected terminals are:
T1=300° and T02=60°; Δ120°
T2=60° and T03=180°; Δ120°
T3=180° and T01=300°; Δ120°
Thus, if a phase angle of 60° degrees could be introduced between the secondary windings of the rotors, a 180° phase shift between each of the secondary windings can be achieved.
T1=300° and T02=60°+60°=120°; 180°
T2=60° and T03=180°+60°=240°; Δ180°
T3=180° and T01=300°+60°=360°; Δ180°
This concept can be graphically illustrated with reference to
From the foregoing discussion, it is clear that a 60° phase angle between the exciter and generator stages is needed obtain the proper secondary winding interconnects by the testing methodology described above. It should be noted that the phase angle is measured in electrical degrees. The actual physical angular displacement in mechanical degrees between either the exciter or generator stages to obtain a phase angle of 60 electrical degrees will vary depending on the number of poles. The physical angular displacement is measured between the poles of either the rotors or stators, and can be expressed by the following equation:
where x is referred to as a pole pitch. Equation (1) assumes that either (1) the secondary windings are wound in the same direction and connected to one another with reverse polarity, or (2) the secondary windings are wound in the opposite direction and connected to one another with the same polarity. For line synchronous generators with (1) the secondary windings wound in the same direction and connected to one another with the same polarity, or (2) the secondary windings wound in the opposite direction and connected to one another with reverse polarity, the pole pitch x can be expressed by the following equation:
Either way, to obtain a 180° phase shift in the secondary windings to effect electrical cancellation of the frequency induced by the angular rotation of the local power source, either the rotors or the stators should have a physical angular displacement of one pole pitch.
As an alternative to physically rotating the rotors or stators, the windings can be offset. First, the physical angular displacement is determined. Applying equation (1) for a six (6) pole three-phase system the pole pitch is:
Therefore, the exciter and generator stages require an physical angular displacement of 20°. This may be accomplished by displacing the winding of two fixed cores if the slot count allows. For example, a 36 slot core with a two slot displacement would result in 20° and is acceptable for six (6) pole three-phase system. This can be achieved by starting the generator group in slot 1, and the exciters group in slot 3. However, a 48 slot core does not result in any combination of 20°, and therefore, phase angle alignment could not be obtained solely by core displacement.
Optimal loading is a function of the phase angle and rotor rpm. As the RPM increases substantially above “synchronous speed”, the phase angle range necessary to meet maximum generator load narrows significantly. Thus, through manipulation of the phase angle of the exciter stage relative to the generator stage, complete control over loading is achieved. A responsive and accurate device must be employed to adequately provide phase angle optimization when variable speed prime movers are used.
The power output is shown at four different phase angles between the exciter and generator magnetic field.
In a preferred embodiment, the generator stator field is tapped and compared with the AC source frequency by a control mechanism to provide a phase error signal to a servo motor. This servo motor positions the exciter stator to optimize generator loading, a function of the phase difference that results from changes in shaft speed. The accuracy and response of the servo motor and its control mechanism are critical to optimize generator loading. Because servo motor control technology is sufficiently advanced, accurate exciter induction compensation can be provided in virtually all electrical generation applications.
Alternatively, the phase angle may be set during the interconnection process. Turning to
T2 to T02=178 volts
T2 to T03=143 volts
T3 to T02=166 volts
T3 to T03=178 volts
The voltage between terminals T2-T02 and T3-T03 are each 178 volts, which is close enough to 180 volts to satisfy one of the required pairs. However, the voltages between the remaining terminals are not close enough to the 156 volts to satisfy the second required pair. However, if the voltages are averaged, the result is 155 volts which is close to the desired voltage. This indicates improper phase angle between the exciter stage and the generator stage. In this case, either the exciter stator, the exciter rotor, the generator stator or the generator rotor can be physically rotated on its axis until the voltages between T2 and T03 and the voltages between T3 and T02 each read 155 volts. In this case, from the vector diagram of
The described embodiments provide an important solution that allows the rotational speed to vary substantially over traditional machinery limits while remaining self-synchronizing. The active controls are simplified to those necessary for safety purposes. The machinery speed maximum limits may be enhanced with simple active control of passive devices. This shows the versatility of the inventor, an inherently acceptable speed range which may be extended by addition of simple passive devices. Thus, any local power source which allows for a minimum speed and exceeds the parasitic losses of the device may be effectively used to supply the utility grid. Such adaptation of local alternative power sources has a major potential for resolving the present energy shortage with minimum adverse ecological consequences.
It is apparent from the foregoing that the present invention satisfies an immediate need for a three-phase line synchronous generator with proper phasing having a constant frequency and voltage output at variable shaft speeds. This three-phase line synchronous generator may be embodied in other specific forms and can be used with a variety of fuel sources, such as windmills, wind turbines, water wheels, water turbines, internal combustion engines, solar powered engines, steam turbine, without departing from the spirit or essential attributes of the present invention. It is therefore desired that the described embodiments be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than the foregoing description to indicate the scope of the invention.
The present application is a continuation of co-pending patent application Ser. No. 11/560,996, filed Nov. 17, 2006, which is a continuation of Ser. No. 11/257,374, filed Oct. 24, 2005, now abandoned, which is a continuation of patent application Ser. No. 10/966,140, filed Oct. 15, 2004, now abandoned, which is a continuation of patent application Ser. No. 10/359,038, filed Feb. 5, 2003, now abandoned, which is a continuation-in-part of patent application Ser. No. 10/247,789, filed Sep. 19, 2002, now abandoned, which is a continuation of patent application Ser. No. 09/587,202, filed Jun. 5, 2000, now abandoned, which is continuation-in-part of patent application Ser. No. 09/338,002, filed Jun. 22, 1999, which issued as U.S. Pat. No. 6,072,303 on Jun. 6, 2000, which is a continuation of PCT application No. PCT/US98/02651, filed Feb. 6, 1998, the priority of each which is claimed under 35 U.S.C. §120. The PCT application No. PCT/US98/02651, as well as this application claims priority under 35 U.S.C. §119(e) to provisional application No. 60/037,723, filed Feb. 7, 1997. All of these applications are expressly incorporated herein by reference as though fully set forth.
| Number | Date | Country | |
|---|---|---|---|
| 60037723 | Feb 1997 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11829840 | Jul 2007 | US |
| Child | 12970432 | US | |
| Parent | 11560996 | Nov 2006 | US |
| Child | 11829840 | US | |
| Parent | 11257374 | Oct 2005 | US |
| Child | 11560996 | US | |
| Parent | 10966140 | Oct 2004 | US |
| Child | 11257374 | US | |
| Parent | 10359038 | Feb 2003 | US |
| Child | 10966140 | US | |
| Parent | 09587202 | Jun 2000 | US |
| Child | 10247789 | US | |
| Parent | PCT/US98/02651 | Feb 1998 | US |
| Child | 09338002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10247789 | Sep 2002 | US |
| Child | 10359038 | US | |
| Parent | 09338002 | Jun 1999 | US |
| Child | 09587202 | US |
