Patent Application
20100019628
1. Related Applications
This non-provisional application claims priority to and the benefit of U.S. Patent Application No. 60/813,735, filed on Jun. 14, 2006, incorporated herein by reference in its entirety.
2. Field of the Invention
The present invention relates to the design and manufacture of an in-situ serviceable high performance rotatable rectifier used in brushless exciters of AC generators.
3. Description of Related Art
Conventional electrical machines, such as AC generators, require a rotating DC field to energize its stationery armature windings. This rotating DC field is obtained from a separate source called an exciter. There are two types of exciters: static and rotating. Static exciters come in the form of circuits providing DC voltage from storage batteries or DC voltage from solid-state components including transformers, rectifiers, and reactors, etc. Rotating exciters come in the form of a rotating generator assembly, which generates a DC voltage used to power a rotating winding (form a rotating DC generator field) within the AC generator. Rotating exciters come in various configurations including those that require brushes to transfer the DC exciting current to the rotating DC generator field, those that require a combination of brushes and a commutator, and those that require no brushes, known as “brushless” exciters. Both brush type exciters and brushless type exciters can be mounted on the same rotatable shaft as that for the AC generator or can be mounted on a separate shaft. The main difference between brushless type exciters and brush type exciters is that in the brushless type exciters, the rotating slip rings of the brush type exciters are replaced with a rotatable (rotating) rectifier assembly.
A rotatable rectifier exciter is an example of a brushless exciter. The rotatable rectifier exciter uses, for example, a three-phase solid-state rotatable rectifier assembly mounted on a rotatable rectifier hub or wheel, which is electrically connected between the rotatable exciter armature and the rotating DC field winding of the AC generator. The rotatable rectifier hub or wheel is typically mounted on a common rotatable shaft, along with the exciter armature and rotatable rotor assembly. As such, the rotatable rectifier hub or wheel rotates with the exciter armature and rotatable rotor assembly. Conventionally, however, the rotatable rectifier hub and the rectifier assembly are both physically and electrically insulated from the exciter rotor and the exciter armature. Recognized by the Applicants, however, is that this physical separation, in particular, results in the exciter assembly being much larger and heavier, and therefore more expensive, than necessary. Also recognized by the Applicants is that the rotatable rectifier hub or wheel can be positioned underneath the exciter armature end turns to conserve space and minimize bearing span or overhang mass to thereby minimize detrimental rotor dynamic issues from operating at high shaft speeds. Further, recognized by the Applicants is the applicability of such configuration to both generators and motors that utilize a rotatable rectifier assembly.
In a typical AC generator using a brushless exciter, the AC output voltage of the AC generator is controlled by controlling the strength of the rotating DC field. Increasing the strength of the DC field increases the AC output voltage. Similarly, decreasing the strength of the DC field decreases the AC output voltage. A voltage regulator control is typically used to control the exciter stationery field, which, in turn, affects the strength of the rotating DC field to thereby provide a stable AC generator output, which matches the load on the AC generator. Thus, in operation, when the rotatable shaft is rotated, an AC voltage is induced in the exciter armature winding, which is then rectified by the rotatable rectifier assembly to provide DC current to the rotating DC field winding of the AC generator. Depending upon the load on the AC generator, the voltage regulator increases or decreases voltage to the exciter stationery field windings to thereby increase or decrease the output of the exciter to correspondingly increase or decrease the strength of the rotating DC field. This operation functions continuously as the load on the AC generator increases or decreases, to provide a stable, well-controlled, AC generator output voltage. Note, in very large generators, a pilot exciter may be used in order to initiate such AC power generation.
In order to rectify the power generated by the exciter armature winding, the rotatable rectifier assembly utilizes a series of diodes, typically at least two per phase in a polyphase system, to provide the rotating DC field. In low speed machines having low speeds and low power densities, conventional pig tail-type diodes carried on a rectifier wheel are adequate. As the shaft speed increases, i.e., at high rotational speeds, centrifugal and centripetal forces result in stress, vibration and balancing issues. The industry has tried to compensate by using, for example, silicon wafer diodes such as those typified by type A390P diodes, manufactured, for example, by General Electric Co. These diodes, however, require a relatively precise contact force between metallic contacts positioned against two spaced apart contact electrodes positioned along the functional axis of the diodes. One methodology of positioning these diodes is to position them within the rotatable shaft of the generator or motor along the axis of rotation to minimize, if not completely negate, the effects of the centrifugal and centripetal forces generated by high-speed rotation of the associated rotatable shaft.
Another more generally accepted methodology has been to fasten the diodes to a rotatable rectifier hub or wheel oriented so that the diode axis is perpendicular to the axis of rotation of the rotatable shaft. Such orientation has been necessitated conventionally because industry has believed that a parallel orientation for silicon wafer-type diodes positioned off the main axis of rotation outside the rotatable shaft would result in unacceptable variations in contact force between diode contacts in high-speed (high spin) electrical machines. Recognized by Applicants, however, is that such orientation results in the rotatable rectifier hub or wheel being much larger and heavier, and therefore more expensive, than necessary. Also recognized by Applicants is that silicon wafer diodes can be oriented parallel to the axis of rotation of the shaft if secured by resin or other bonding material capable of immobilizing the diodes to prevent centripetal force induced damage or degradation. Further, recognized by the Applicants is the need for an enhanced cooling system for the silicon wafer diodes if they are to be embedded in such material.
In view of the foregoing, embodiments of the present invention provide a brushless exciter apparatus including a rotatable rectifier hub assembly and methods of forming the brushless exciter, specifically designed for use in high performance and high speed electrical machines applications. An embodiment of a full-wave rectifier of the present invention, for example, features a unique compact design that can be conveniently located integrally with the exciter of a high performance electrical machine. Advantageously, as a result of such design, the entire rectifier assembly can be replaced as an assembly as needed whenever any of the diodes fail. The design also advantageously can accommodate large diameter devices for advanced high performance pulsed generator designs.
More specifically, embodiments of the present invention provide an alternating current generator brushless exciter apparatus. For example, a brushless exciter apparatus according to an embodiment of the present invention can include a rotatable shaft having a shaft axis of rotation, a stator, and an exciter rotor assembly positioned along an axial extent of the shaft and rotating within the stator. The exciter rotor assembly can include, for example, a rotor core formed of, for example, a plurality of laminations defining an rotor stack clamped between a pair of end plates, and an exciter armature having end turns extending beyond either side of an axial extent of the rotor core. The rotor core can also include an internal clamping tube positioned to axially clamp the rotor stack between the pair of end plates. The exciter apparatus can also include a rotatable rectifier hub assembly including a rotatable rectifier hub carrying at least one pair of diodes for rectifying AC power and positioned along an axial extent of the shaft adjacent the rotor core, with at least portions positioned radially between an extent of the exciter armature and outer surface portions of the shaft. Advantageously, in this embodiment of the apparatus, the end plates of the rotor core can include an axial extension which supports the exciter armature and functions to separate the exciter rotor armature winding from the rotatable rectifier hub.
Embodiments of the present invention also provide a rotatable rectifier hub assembly adapted to be positioned along an axial extent of a rotatable shaft of an electrical machine. For example, a rotatable rectifier hub assembly according to an embodiment of the present invention can include a hub body, and at least one diode assembly carried by the hub body. The at least one diode assembly includes at least one pair of diodes for rectifying AC power that are oriented substantially parallel to the axis of rotation of the shaft. The hub body includes an annular recess extending axially inward and forming an annular cavity for receiving the at least one diode assembly. The annular cavity is subdivided to form a diode resin casted cavity section. Correspondingly, according to this embodiment of the rotatable rectifier hub assembly, the at least one diode assembly is positioned in the diode resin casted cavity section of the annular cavity. An AC bus ring and a pair of DC bus rings are also positioned within the annular cavity and extend through the at least one diode assembly. The diode resin casted cavity section is substantially filled with resin or other material to immobilize the diodes to thereby enhance control of the diode clamping force. Advantageously, such configuration can prevent centripetal force induced damage to the at least one pair of diodes during high speed rotation. Cooling is provided by the a plurality of cooling blades positioned circulate air over the AC and DC bus rings which thermally conduct heat from the diodes from within the resin casted cavity section or sections.
Embodiments of the present invention further provide methods of forming an alternating current generator brushless exciter and methods of forming a rotatable rectifier hub assembly adapted to be positioned along an axial extent of a rotatable shaft. For example, a method of forming an alternating current generator brushless exciter can include the steps of positioning an exciter rotor assembly including a rotor core and an exciter armature along an axial extent of a rotatable shaft, positioning at least one diode assembly (including a pair of diodes for rectifying AC power) within a rotatable rectifier hub assembly, and positioning the rotatable rectifier hub assembly along an axial extent of the rotatable shaft adjacent the rotor core with at least portions of the rotatable rectifier hub assembly radially between an extent of the exciter armature, e.g., end turns, and the rotatable shaft. The exciter armature can have end turns extending beyond either side of an axial extent of the rotor core. The rotor core can include a plurality of laminations defining a rotor stack clamped between a pair of end plates.
Synergistically, a method of forming a rotatable rectifier hub assembly adapted to be positioned along an actual extent of a rotatable shaft can include the step of positioning at least one, but preferably three, diode assemblies each including at least one pair of diodes for rectifying AC power within a hub body of a rotatable rectifier hub assembly, so that each of the diodes are oriented substantially parallel to the axis of rotation of the shaft when the rotatable rectifier hub assembly is positioned along the axial extent of the rotatable shaft. Specifically, the method can also include the step of subdividing an annular cavity of the hub body to form at least one, but also preferably three, diode resin casted cavity sections, positioning the respective diode assemblies separately in each of the diode resin casted cavity sections, and substantially filling the diode resin casted cavity sections with resin or other bonding material to immobilize the diodes to thereby enhance control of diode clamping force, preventing centripetal force induced damage to the respective diodes of each of the diode assemblies during high speed rotation.
In general, embodiments of the present invention provide an attractive upgrade to existing older rectifier designs in use today. Specifically, embodiments of the present invention are desirable for high power pulsed generator applications where very high power and responsive excitation currents are required for the generator. The rotatable rectifier bridge of the rotatable exciter, for example, is modular in design, simplifying service procedures and cost. Accordingly, such design can accommodate large diameter rectifier devices and operate at very high speeds.
So that the manner in which the features and advantages of the invention, as well as others which will become apparent, may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it may include other effective embodiments as well.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Prime notation, if used, indicates similar elements in alternative embodiments.
The rotor core 43 of the exciter rotor assembly 37 can also include an exciter armature 49 having end turns 50 extending beyond either side of an axial extent of the rotor stack 45. Accordingly, as perhaps best shown in
Accordingly, the rotatable rectifier assembly 41 of the exciter apparatus 31 can be axially positioned along an axial extent of the shaft 35 adjacent the rotor core 43, and can be, in certain embodiments, substantially radially positioned under the confines of the end turns 50 of the armature 49. That is, the rotatable rectifier hub assembly 41 can be radially positioned between inner surface portions of the end plate axial extension portion 57 of the end plate 53 and outer surface portions of the shaft 35 radially adjacent the end plate axial extension 57 of the end plate 53, in certain embodiments. Note,
As perhaps best illustrated in
As perhaps best shown in
As perhaps best shown in
Similarly, one of the DC bus rings 87, 89, is positioned physically opposite the AC bus ring 91 and in electrical contact with the anode of one of the diodes 63, 65, with the other also physically opposite the AC bus ring 91 and in contact with the cathode of the other one of the diodes 63, 65. Above exemplary configuration, if the diodes 63, 65, are axially oriented with the cathodes facing side wall 81, DC bus ring 87 is in electrical contact with the anode of diode 63 and DC bus ring 89 is in electrical contact with the cathode of diode 65. This configuration arrangement similarly applies to other diode assemblies 61, if installed.
As noted previously, wafer diodes have very sensitive clamping requirements. In order to support the diodes 63, 65, and other rectifier elements in high-speed environments, especially when oriented parallel to the shaft axis of rotation 39, they can be first clamped to/between the bus bars/rings 87, 89, 91. Accordingly, as perhaps best shown in
As perhaps best shown in
In order to support the diodes 63, 65, and the other components of the diode assemblies 61 in high-speed environments, especially when the diodes 63, 65, are oriented parallel to the shaft axis of rotation 39, the diode resin casted cavity section 75 can be substantially filled with resin 111, or other bonding material known to those skilled in the art, to immobilize the components of the diode assembly 61, to thereby enhance control of diode clamping force and to thereby prevent centripetal force induced damage or degradation to the diodes 63, 65, during high speed rotation. As described previously, wafer diodes are extremely sensitive to clamping force variations. By positioning the diodes 63, 65, parallel to the axis of rotation, axial clamping force can be precisely controlled. This, however, assumes that the radial forces generated by rotation of the shaft 35 do not interfere with the integrity of the “stack” of clamped diode accessory components, described above. In order to maintain the integrity of the “stack,” the bonding material, e.g., resin 111, is positioned within the resin casted cavity section 75 to immobilize the diodes 63, 65, thereby mitigating the large centripetal forces that would otherwise negatively impact the relatively sensitive clamping requirements.
The application of bonding material, e.g., resin 111, however, would otherwise tend to disrupt cooling the diodes 63, 65. Accordingly, as described above, embodiments of the rotatable rectifier hub assembly 41 have annular shaped DC bus rings 87, 89 (see, e.g.,
Still further, and as perhaps best shown in
Embodiments of the present invention also provide methods of forming an alternating current generator brushless exciter 31 and methods of forming a rotatable rectifier hub assembly 41 adapted to be positioned along an axial extent of a rotatable shaft 35. For example, as shown in
As shown in
The method also includes the step of positioning this ring-diode assembly arrangement (
The method further includes connecting airfoils 121 to the rotatable rectifier hub 41 (block 161) to provide airflow over the AC bus ring 91 and the DC bus rings 87, 89 to thereby enhance sinking heat (thermal conduction) from the respective pair of diodes 63, 65, from each diode assembly 61.
The unique design and positioning of the rotatable rectifier hub assembly 41 provides several benefits. For example, this design addresses the special needs of extreme power density, continuous and pulse duty AC generators. The design allows for the formation of a three-phase rectifier bridge having a power density rating in excess of 180 MW/m3. The design is unique as compared to conventional designs that are too heavy and cumbersome to be useable in high speed applications. The design is simplistic yet robust as compared to conventional designs. The design is also compact enough to permit its installation inside the generator, beneath the end turns of the exciter rotor assembly, yet it can accommodate large diameter rectifier devices. This design can be used in AC generators including both conventional and modem high power density designs. It is uniquely adaptable to extreme condition pulsed duty AC generators. The design of the rotatable rectifier hub assembly 41 can also be implemented in motors requiring a rotating DC field.
This Application is related to U.S. Patent Application No. 60/813,735 by Kitzmiller et al. titled “High Performance Rotating Rectifier for AC Generator Exciters”, filed Jun. 14, 2006, U.S. patent application Ser. No. ______ by Werst et al. titled “Rotor Assembly and Method of Assembling a Rotor of a High Speed Electric Machine” filed Jun. 13, 2007, U.S. Patent Application No. 60/813,067, by Werst et al. titled “Apparatus and Method for Clamp ______ Laminations in a High Speed Electric Motors”, filed Jun. 13, 2006, PCT Patent Application No. by Lewis et al. titled “Fabrication of Heat-Treated Laminations for High-Speed Rotors in Electrical Machines” filed Jun. 13, 2007, U.S. Patent Application No. 60/813,680, by Lewis et al. titled “Fabrication of Heat-Treated Laminations for High-Speed Rotors in Electrical Machines, filed Jun. 14, 2006, and U.S. Patent Application No. 60/814,017, by Jordan et al. titled “Electric Machinery Laminated Cores With Insulating Laminations”, filed Jun. 15, 2006, each incorporated by reference in their entireties.
In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims. For example, although the exemplary embodiments focused primarily on AC generators, the rotatable rectifier hub assembly can also be implemented in other electrical machines requiring a rotating DC field. Also, although the exemplary embodiments described a laminate-type rotor core, other rotor core configurations are within the scope of the present invention.
This invention was made with government support under contract no. N068335-00-C-0189 SC B000702 awarded by the United States Navy/General Atomics Division. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60813735 | Jun 2006 | US |
