Patent Grant
9154024
The present invention relates to electrical generation devices, including stator/rotor design and assembly, and systems and methods for support structure. The field of the invention includes the design, manufacturing and operation of rotating electromagnetic machines—typically called electric motors or electric power generators.
In principle there are two main types of drive trains used in wind turbines. The first type, as shown in
The size and design of a direct drive generator is influenced by its rotational speed and by the desired power output. Assuming constant rotational speed, the two primary factors in power output are the amount of active material and the radial distance of the active material. Accordingly, for a desired or optimal power output it is possible to reduce the necessary amount of active material by increasing the diameter of the direct drive generator. Thus, it is advantageous for direct drive generators with low rotational speeds, such as direct drive generators used in hydro and wind turbines, to have a large outer diameter.
While the large outer diameter has advantages, it also causes numerous issues for direct drive generators. Among other problems, the large outer diameter causes problems with transporting, lifting, assembling, repairing, and replacing the direct drive generator. These problems are due not only to the size of the device (which significantly impacts transport) but also the weight of the direct drive generator. For example, for typical rotating electric machines, the air-gap (the distance between rotor and stator) is kept no larger than a few millimeters in order to avoid excessive magnetization requirements. In order to closely maintain this air-gap, in conventional rotating electric machines the rotating and stationary parts of the machine are relatively stiff, structurally, on an individual basis. In addition, the support structure, commonly a bearing system is also very stiff. An additional constraint is that the components that affect the shape and dimensions of the parts facing the air gap between the rotating and stationary parts must be produced and assembled with a high degree of precision as the nominal air gap of such machines is typically less than 0.375″ on a diameter that can approach 144″. Additionally, the heavy weight of a multi-megawatt generator of conventional design necessitates additional infrastructure support in the turbine tower and related components, which adds cost and complexity.
As partial solutions to these problems, there have been suggestions on dividing the parts of the generator:
In WO 98/20595 A1 a stator for a rotating electric machine is disclosed comprising a stator core and a winding. The stator core is provided with stator teeth extending radially inwards towards a rotor. Each stator tooth is configured as a number of tooth sections joined axially into a stator tooth plank. That stator tooth planks are fitted together side-by-side thus forming a section of the stator core. This construction makes the transport of parts of the rotating electric machine to the site of erection partially easier because the stator can be assembled on site. However, this construction requires a stator housing having relatively large outer dimensions.
From U.S. Pat. No. 4,594,552, an armature winding of a split stator is known. The split stator has a slotted core divided by at least two circumferentially-spaced split lines to facilitate the assembly and the disassembly of the split stator. The armature winding comprises armature coils in the slots of the stator core connected to provide poles and arranged to provide a plurality of armature coils divided at the split lines. Connecting and disconnecting means are provided to connect and disconnect the armature coils when the split stator is assembled and disassembled, respectively. This construction, however, also requires a stator housing having relatively large outer dimensions.
U.S. Pat. No. 5,844,341 describes an electric generator to be driven by a low speed device such as wind turbine. The generator consists of one or more rotor rings of many permanent magnets of alternating polarity and coaxial stator rings of many laminated yokes, each yoke defining slots to locate coils. The yokes and coils form modules which are supported by beams relative to the rotor rings. The drawbacks of this configuration are that the electromechanical properties in this form of modular construction, with single polar pairs separated by air gaps, may be disadvantageous; that a possible dismantling of a single stator module can require that the whole generator has to be opened in situ thus implying risk of humidity, dirt, etc.; and that it may be cumbersome if the stator module has to be taken out in a disadvantageous direction.
U.S. Pat. No. 6,781,276 B1 describes a generator for a wind turbine comprising a stator and a rotor. The stator has a number of stator modules that are individual and which may be installed, repaired and dismantled individually and independently of each other. This generator has no part larger than the air gap diameter. But even if no part is larger than the air gap diameter, the largest element to be transported still has a substantial size, given that the rotor is a single piece. In its completed form, this rotor is fitted with strong permanent magnets and needs to be covered by a nonmagnetic layer, e.g., wood or polystyrene of a certain thickness, during transportation. And while the dimensions of the rotor are smaller than the dimensions of the finished generator, it is still, at maybe 5 m diameter and 1.5 m length, a very substantial piece of equipment to transport.
U.S. Patent Publication No. 2009/0134629 describes a generator for a wind turbine comprising ring-segmented-shaped stator segments and ring-segment-shaped rotor segments. The stator and rotor are separated by a radial air gap wherein each ring-segmented-shaped stator segment is located radially outward from the ring-segment-shaped rotor segments. By using a ring shaped stator and ring shaped rotor, the invention requires axial width in order to provide the amount of active material desired at a certain diameter. Some further reduction in weight is described by reducing the supporting structure that limits the axial movement of the rotor and stator.
Although present devices are functional, they are not sufficiently efficient, effective or otherwise satisfactory. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.
Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents and alternative constructions that fall within the spirit and scope of the invention as expressed herein.
The present invention can provide a system and method for reducing the weight and size of transportable components of a direct drive generator. In an exemplary embodiment, a direct drive or directly driven axial flux generator is provided, the generator comprising a stator having at least one stator element for power generation and a rotor rotatable around a center axis of the generator having at least one rotor element for power generation; the generator having an axial air gap between the stator element and rotor element, wherein the at least one stator element and the at least one rotor element are located at substantially the same radial distance from the center axis so as to allow for electrical generation during their relative motion. The generator may further comprise arc-shaped axially connectable stator supports, the stator elements being axially and circumferentially attached to the arc-shaped supports of the stator, wherein junctions between the arc-shaped supports of the stator and stator elements are located substantially at a position on the circumference of a radius which is substantially larger than the center axis of the generator; with the complete assembled generator having the appearance of a disc-shaped ring having a very large, somewhat open center with a spoked or other similar connecting structure.
In a preferred embodiment, the present invention can include a direct drive generator made with permanent magnets attached to the rotor and with a segmented iron-less stator made using printed circuit board manufacturing processes or some other iron-less stator, such as wire-wound coils. This type of generator is preferred because the permanent magnets allow for a smaller machine and the iron-less stator allows a cog-free operation and alleviates the disadvantages of magnetic attractive forces between rotor and stator, such disadvantages including extra load on bearings, difficulties in maintaining gaps between rotor and stator, and difficulties in assembly on site. In exemplary embodiments, the axial gap between the rotating rotor elements and the stationary stator elements is maintained by means that allow a flexible non-rigid construction. This flexible, detachable, segmented system allows a complete large diameter generator to be transported in sections and assembled on site. Additionally, the axial-gap maintenance means eliminates the need for heavy, rigid supports that are usually required to maintain electromagnetic gaps in conventional machines. Furthermore, the axial flux generator incorporates a segmented stator made from multi-layered printed circuit boards and a segmented iron rotor and permanent magnets to generate permanent magnetic flux. Furthermore, the invention concerns a wind turbine incorporating such a direct drive generator.
In another embodiment, the present invention comprises a direct-drive axial flux generator comprising an arc-shaped, sectioned stator having at least one stator element operative for the electrical power generation and an arc-shaped, sectioned rotor having at least one rotor element operative for the electrical power generation, the generator having an axial air gap between the stator element(s) and the rotor element(s), wherein the stator(s) and rotor(s) are assembled and constructed together in transportable sections, along with supporting elements of the stator sections and rotor sections. The stator element(s) and rotor element(s) are located substantially at the same radius in relation to the center axis of the generator. That is, the stator element(s) and rotor element(s) are positioned to overlap radially, at least partially, in order for power generation. According to the invention, the stator of the generator is comprised of arc-shaped, sectioned components including supporting structure and stator element(s) and rotor element(s). The stator as a whole comprises a plurality of single, manageable sections, the sections being attached to each other in a detachable way.
In a preferred embodiment, the connections in particular, between the arc-shaped supporting elements and the arc-shaped stator elements, are non-destructively detachable. The assembly and the disassembly of the stator, rotor, and support structure, and thus of the generator, on the site of erection are simplified. In the case of a wind turbine, the whole mounted generator may be lifted into the nacelle using a crane. Alternatively, the generator pieces may be lifted into the nacelle, with the nacelle on the ground or on the tower, for assembly. The significantly lighter and manageable parts and smaller pieces of the generator can be carried into the nacelle where the generator can be assembled, repaired or disassembled.
According to an embodiment of the invention, the rotor of the generator is made up of a plurality of arc-shaped rotor sections, each rotor section having a one or more magnets affixed to its surface. Said rotor sections are attached by arc-shaped rotor supports, wherein the detachable junctions between adjacent arc-shaped sections are located substantially at positions on the circumference at an outer radius in relation to the center axis of the generator. The radial positions are substantially the same to allow for power generation. The arc-shaped rotor supports and the rotor elements built as a completely assembled generator can have a substantially open-centered disk-shaped configuration, preferably with a truss-shaped supporting structure. The support structure can be attached to a center shaft or to the rim of a fixed support structure that sits at the largest diameter of the generator and that is attached to another stationary support structure inside the turbine nacelle. The rotor as a whole also comprises a plurality of single manageable elements and segments which are typically attached to each other in a detachable way. The connections between the arc-shaped supporting elements of the rotor and the rotor elements are preferably non-destructively detachable. As a consequence, the transport of the generator is simplified. The rotor, along with the stator, can be transported in parts wherein each part has lesser dimensions and a lower weight than a fully-assembled generator. In particular, the dimensions of an arc-shaped rotor support, along with the stator and rotor elements, is preferably significantly smaller than the diameter of the completely assembled generator.
In an embodiment of the invention, the junctions of the stator sections and the junctions of the rotor sections are located substantially at the same circumferential position in relation to the center axis of the generator, which is advantageous for assembly and disassembly of the generator.
By arcuately sectioning the stator, rotor, and support structure into at least two sections, the overall dimensions of the transported assemblies are within easily shippable sizes. According to an embodiment of the invention, each shippable section is comprised of multiple smaller stator sections and rotor sections attached to an arc-shaped supporting element such that assemblies are easily shippable and ready to assemble on site. Thereby, the arc-shaped stator, rotor, and support sections form a complete generator in a complete circular shape once assembled and connected at junctions located in at least two positions at the circumference of the generator.
According to one variation of the invention, an arc-shaped stator section may comprise a stator element for electrical generation, a supporting component to hold the stator element, and a connection component to connect the supporting component to the supporting component. Each of the stator element, supporting component, and connection component may be arc-shaped in order to facilitate connection with adjacent arc-shaped stator sections. The connection component may be arranged on the outer circumference of the supporting component. Moreover, the invention may further comprise a first joining element to connect the arc-shaped stator section to an adjacent arc-shaped stator section on a first side, and a second joining element to connect the arc-shaped stator element to an adjacent arc-shaped stator element on a second side.
In another embodiment, the present invention further describes an arc-shaped rotor section that may be used in conjunction with, or separately from a sectioned stator. The arc-shaped rotor section may comprise a rotor element for electrical generation, a supporting component for holding and supporting the rotor element, a connection component to connect the supporting component to a rotor element. The rotor element, supporting component, and connection component may all be arc-shaped in order to facilitate connection with adjacent arc-shaped rotor sections. In one embodiment, the rotor elements may extend radially outward from the connection component and supporting component. In another embodiment, the rotor elements may extend radially inward, such that the rotor elements are free floating on the side that is radially inward.
In an embodiment of the invention, each rotor element is at least partially arranged axially on either side of a stator element. It is also possible that two or more rotor elements are at least partially arranged in axial stacks, wherein the axial stack if formed by alternating stator elements and rotor elements. Thereby the stator elements and the rotor elements for power generation are arranged oppositely to each other with an intermediate air gap. For example, a stator section and two rotor sections can be assembled to form one rotor/stator/rotor unit. Likewise, a stator element and two rotor elements can be assembled to form one rotor/stator/rotor unit. As additional stators (and/or stator components) and rotors (and/or rotor components) are combined, they could follow the same basic pattern. Alternative patterns, such as rotor/stator/rotor/rotor/stator/rotor or rotor/stator/stator/rotor could also be used.
In a further development of the invention, a stator section and rotor section(s) are able to be at least temporarily supported against each other. Preferably each stator section comprises a first supporting removable shim and each rotor section comprises a second supporting removable shim, wherein the first supporting removable shim of a first stator section and the second supporting removable shim of a corresponding first rotor section are able to be at least temporarily supported against each other. Preferably each stator connection element of a stator section comprises at least one first supporting removable shim and each rotor connection element of an arc-shaped rotor section comprises at least one second supporting removable shim. By means of the supporting removable shim, a rotor section is able to rest on a stator section when the generator and the sections are transported, assembled or disassembled. Through the use of shims, an air gap remains between the stator elements and the rotor elements. As a consequence the transport, assembly and disassembly are simplified.
According to another embodiment of the invention, a stator section comprises at least one stator element made from a multi-layered printed circuit board, as defined in patent application number PCT/US2010/000112 as a stator segment. And a rotor section comprises at least one, but typically a plurality, of permanent magnet(s) and associated back iron as a rotor element(s). In order to avoid confusion with the terminology in PCT/US2010/000112, which is incorporated herein by reference, the present application uses the term “stator sections” to refer to arc-shaped portions of a stator structure. A stator section comprises a stator support, at least one stator element for electrical generation (which may be a printed circuit board stator segment as described in PCT/US2010/000112), and other stator components.
In an embodiment of the invention, the stator sections, the arc-shaped stator supports, the rotor sections, and the arc-shaped rotor supports comprise circumferential structures which allow for axial mounting of the stator elements and supporting elements. Thereby the circumferential axial flanges preferably extend substantially in the directions of the axial flux and preferably extend substantially axially in relation to the center axis of the main shaft. In this way the stator and rotor sections can be comparatively simply attached to the respective arc-shaped supporting elements.
In another exemplary embodiment, the present invention incorporates a sectioned easily shippable support structure to which a number of detachable, multi-layered, printed circuit board stator segments and an associated set of detachable rotor sections. Preferably, the rotor sections, to which permanent magnets are affixed, are axially positioned on each side of the stator elements (in this case, multi-layered, printed circuit board stator segments) at a specified axial gap, which is maintained by a gap control means during operation after the generator is assembled and installed into the turbine. The shippable support structure and associated stator and rotor components are designed to be easily assembled on the site of turbine erection to form a complete operating generator. One embodiment of the generator is approximately eight meters in diameter as a complete assembly, but is transported in quadrants that are no greater than four meters in the vertical dimension, thus allowing transportability.
In another embodiment, the invention consists of maintaining a clearance between the rotating and stationary parts of rotating electromagnetic machines, such as a direct drive generator, by purposely making one of the rotating or the stationary parts structurally “soft” or compliant, and the other relatively stiff, then providing a device or mechanism to establish and always maintain the minimum clearance desired by transmitting a force in a suitable direction from the stiff member as it encroaches on the desired minimum clearance, to the “soft” member, thereby pushing the soft member away to maintain the desired clearance. Some of the approaches for establishing and maintaining the minimum clearance distance between the moving rotor to the stator support structure involve either mechanical (i.e., contacting) devices (e.g., rollers or low coefficient-of-friction pads), pneumatic devices, magnetic devices, electromagnetic devices, or combinations thereof. In order for a magnetic or electromagnetic device to be used to maintain the clearance and get around the physics that precludes such a scheme from working on conventional machines, the stator should not contain ferromagnetic materials. Such stators are known in the industry as “air core” stators because the volume of the stator responds to magnetic fields in the same way as air responds.
As previously stated, the above-described embodiments and implementations are for illustration purposes only. Numerous other embodiments, implementations, and details of the invention are easily recognized by those of skill in the art from the following description.
Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:
In the following detailed description, and in the attached drawings, the present invention is described relative to a wind turbine. This is for description only and is not intended to limit the scope or use of the present invention. The present invention provides a generator, and components thereof, wherein the transport of the generator, the construction of the generator, and/or the repair of the generator is simplified. While it is a further object of the invention to incorporate the described generator into a wind turbine, the present invention is not limited to wind turbines.
Referring first to
The size limit for the largest component in direct drive generators depends upon several economic factors—including the transportation cost. Consider a rotor as an example. A one-piece rotor will often be produced in a large steel casting facility. While these facilities often produce very large components for industries such as ship building, the casting facility for these industries is often on-site or nearby so there isn't added cost or complexity for transporting the castings. For other industries, however, such as the wind turbine industry, the steel casting facility is typically not on-site or nearby. Accordingly, the generator and/or the generator components will have to be transported from the production facility to the assembly plant and from the assembly plant to the wind farm. Thus, in certain industries the transportability of the components and the cost of transportation become important factors.
In the United States, an approximate limit on height is around 4.2 to 4.9 meters due to the need to fit under highway overpasses and bridges. When the finished generator size is greater than the size that can be trucked across the country, the generator needs to be designed for segmentation and assembly on-site. Moreover, because certain pieces, such as the stator, rotor(s), and housing have very large diameters, it is likely that these components will also need to be produced in pieces or sections. The pieces can then be assembled on-site, or assembled into subassemblies where the subassemblies are shipped to the installation location and the final generator assembly is completed on-site.
For purposes of illustration and example, the direct drive generators 2000 in
Accordingly, one embodiment of the present invention is a direct drive generator with segmented or sectioned components, including a sectioned stator and/or a sectioned rotor, to reduce the height dimension for purposes of transportation. In addition, the reduced size of the each component provides for reduced weight during lifting and assembly. The present disclosure describes use of a sectioned stator and/or a sectioned rotor for an axial flux motor or generator, allowing the stator and/or rotor portions of the generator to be produced in smaller pieces. The smaller size makes them less costly to transport and also facilitates any machining of the stator and/or rotor sections that may be required. The sectioned stator and rotor allow for partial assembly of the stator and/or rotor in the assembly plant. The stator and/or rotor subassemblies may then be transported to their final destination (e.g., the wind farm) for final assembly on-site during installation.
In another embodiment, as shown in
The rotor frame structure may be a bolt-together assembly, a welded assembly, or cast pieces that are put together with the magnet carriers to make the transportable rotor sub assemblies. In one embodiment, the present invention may comprise rotor quadrants assembled and shipped to the installation site. In another embodiment, six (6) rotor segments may be used. The selection of the number of segments will depend, in part, on the maximum desired height.
Referring now to
The cross-section view in
As discussed, one advantage of the present invention is improved transportability. As shown in
In
Now referring to
Referring first to
In
One option for reducing or eliminating mechanical contact is to use a pneumatic device to provide pressured air.
In
In the embodiment in
In
In a still further embodiment of the invention,
The air gap control system assembly 3000 according to the present invention may be used in many applications where maintaining a constant gap distance is desired for machine performance or safe operation. By way of example only, the air gap control system 3000 may be used with an axial rotor/stator/rotor assembly 2000 shown in
The first annular rotor 2200(a) is attached to a rotating rim of a bearing 1400 with structural support members 2210. Hub 1200 is fixedly attached to an axle (not shown) extending through central opening of the stator hub 1500. The opposing annular rotor 2200(b) is attached to the first annular rotor 2200(a) through spacer blocks 2230 located at the outer diameter of the rotor/stator/rotor 2000 assembly, such that the two annular rotor segments 2200(b) and 2200(a) rotate together, and deflect primarily in the axial direction as a single, structurally rigid subassembly. The stator 2100 is attached to stator clamp ring 2130 which is connected to a stationary rim of stationary stator hub 1500 by means of structural support members 2110. Stator hub 1500 is fixedly attached to a support structure and/or housing arrangement (not shown) which further maintains the fixed orientation of the non-rotating components of the rotor/stator/rotor assembly 2000.
As shown in
By means of the structural support members 2210 and 2110, the annular rotors 2200(b) and 2200(a) and the annular stator 2100 are held in relatively fixed axial positions with respect to each other. The air gap control system 3000 exerts a repulsive force between the stator assembly 2100 and the rotor assemblies 2200(b) and 2200(a) such that, if relative deflection between the rotor and stator assemblies were to occur due to external loading or inertial acceleration, the air gap control system 3000 will produce a force that causes the flexible member(s) to maintain a nominal, location, in this case where the stator assembly 2100 is centered between the rotor assemblies 2200(b) and 2200(a).
This primarily axial translation of the stator assembly 2100 results in a relatively uniform gap alignment along the radial direction of the generator or motor such that the gap distance of the inner diameter between annular rotor 2200(a) and annular stator 2100 is kept relatively the same as the gap distance at the outer diameter even if the annular stator 2100 has been subject to axial translation. Similarly, the gap distance of the inner diameter between annular rotor 2200(b) and annular stator 2100 is kept relatively the same as the gap distance at the outer diameter even if the annular stator 2100 has been subject to axial translation. The repulsive forces of the magnets 3040, 3042, 3044 and 3046 of the air gap control system 3000 force the annular stator 2100 to re-center itself between the annular rotors 2200(b) and 2200(a) even in the presence of a constantly applied external force to the rigidly mounted rotor assemblies.
A section of annular rotor 2200(b) as shown in
A detail view of the full air gap control system assembly 3000 partially shown in
In the preferred embodiment, magnets 3040, 3042, 3044 and 3046 are neodymium-iron-boron (NdFeB) permanent magnets, and per this arrangement, assembly 3000 is equivalent to a two-sided permanent magnet bearing. Because these opposing magnets 3040 and 3044 as well as 3042 and 3046 are placed in a nearly continuous ring around both the rotor assemblies 2200(b) and 2200(a) as well as both faces of the stator assembly 2100, the effect of eddy current drag, which would be induced by an alternating magnetic field at a given location due to the relative motion, is thereby minimized.
In the present embodiment, rotor back iron 3034 is made from a magnetically permeable material, such as iron or steel, and it provides both a return path for flux to pass from one row of magnets 3042 to the adjacent row of magnets 3040 as well as structural rigidity to react the attractive force between the two annular rotor segments 2200(b) and 2200(a) as shown in
An alternative assembly 3000 is shown in
The magnets 3040 and 3044 are oriented in such a manner that the polarity of axially opposing magnets is in opposite directions. Magnets 3042 and 3046 are also oriented in such a manner that the polarity of axially opposing magnets is in opposite directions. This arrangement results in magnet pairs 3040 and 3044 as well as 3042 and 3046 that have identical polarity facing either side of a physical gap. Through this arrangement, there is a repulsive force between magnet pairs 3040 and 3044 as well as 3042 and 3046, and this force is known to increase as magnet pairs are brought more closely together by reducing the physical gap. In the nominal, equilibrium position shown in
The air gap control system 3000 is designed in such a manner that the axial location of the stator 2100 is nominally centered between annular rotors 2200(b) and 2200(a), and any relative deflection of the stator 2100 with respect to either of the rotor assemblies 2200(b) or 2200(a) induces a centering force that acts to return the stator to its nominally centered location between rotor assemblies.
Additionally, the repulsive forces of the magnet pairs 3040 and 3044 as well as 3042 and 3046 act to reduce out-of-plane rotation of the stator assembly 2100 in relation to the rotor assemblies 2200(b) and 2200(a) by reacting against bending moments as shown in
While the preferred embodiment utilizes a magnetic bearing as described above, it is known that other means exist by which the air gap control system exerts a force which, in the case of an axially oriented motor or generator, enables a primarily axial translation of at least one rigidly supported member mounted in opposition to at least one other rigidly supported member so that the gap distance at all lateral points between the two members is maintained relatively constant regardless of the dynamic changes in external loading on the rigidly mounted members of the assembly. The preferred and exemplary embodiments described herein have numerous advantages. Generally speaking, an axially soft (or less stiff) structure and an axially stiff support structure for a rotor and stator may be used to reduce loads on any of the force transmitting mechanisms between the rotor and the stator. In the disclosed embodiments, this allows a stiffer rotor to force the stator to follow the rotor, should the rotor deflect from any outside forces. The flex in the soft structure allows for maintaining the necessary axial air gap without exceeding the capacity of either the non-contacting force transmission mechanisms or the contacting force mechanisms over the full range of movement of the rotor. The present invention also can help prevent exceeding the load capacity of the mechanical snubbing material in a contacting force transmission concept. Using combined mechanisms, devices and methods can further reduce the undesirable, rapid wear of the mechanical snubbing material by preventing contact for substantial lengths of operating time (in which case it will be acting like a guide and not like a snubber) while transmitting axial (and torsional) force to the stator.
Using a PCB stator in the present invention differs significantly from iron-core machines of the axial or radial gap configurations. In those machines, the magnetic attraction of the stator to the rotor (and visa versa) is one or two orders of magnitude higher than the forces that make torque from electricity (as a motor) or provide available torque to convert to electricity (as a generator). Thus, the structure of the stator and the rotor, as well as the bearing system between them, must be designed to resist these forces to maintain the physical air gap at rest (for permanently excited machines such as the types that use permanent magnets on the rotors or in the stators) and in operation (all rotating electric machines). Further, in such machines, departures from true concentricity of the stator and the rotor of more than ˜10% of the nominal air gap can cause output waveform distortions that can generate undue transmission or other load related losses.
The unique features of the axial gap, air core machines produced using the design and manufacturing methods of U.S. Pat. No. 7,109,625, entitled Conductor Optimized Axial field Rotary Energy Device, dated Sep. 19, 2006, allow the mechanical gap to be set considering tolerances with relatively small machines, while the inside diameter of the stator is left unsupported. As the diameter is increased, the use of tolerances alone to ensure the air gap is inviolate under all operating conditions is impractical if weight and cost are design objectives. The mass of the structure needed to make a stiff enough support to maintain the air gap at machine diameters over 8 meters will necessarily exceed the electromagnetic mass by more than an order of magnitude. In order to reduce costs and weight, the present invention may be employed. This includes using a low axial stator stiffness, for axial air gap machines, combined with a system and method to guide the stator axial movement so that it follows any rotor movement in large diameter, axial air gap, air core, electric machines so that a minimum physical air gap between the rotor and stator is maintained under all conditions. The details of the system and method to transmit the rotor's axial motion to the stator support system so that the support system moves the stator far enough, and timely enough, to avoid contact are numerous, and form a number of embodiments of this design. Other means will be apparent to others practiced in the art. Similar concepts may be used if they may be employed to maintain an air gap between parts with relative motion that cannot touch in operation, and they operate by having one structural element that is significantly stiffer that also provides a spatial reference point and location from which a force is transmitted to the softer structural element to guide it into the desired position from that reference point, such embodiments will be considered to be within the scope of this invention.
Further, in radial field machines where the material selection and geometry of the machine produces the same “air core” results (no magnetic attraction between the rotor and the stator), a similar approach can be used. And, in cases where the rotor is more amenable to being the more flexible element of the system, the same concept applies. Therefore axial and radial field machines with rotors that exhibit sufficient compliance to follow a stiffer stator structure, should it be subject to motion that can close or distort the air gap, should also be understood from the present disclosure
In an embodiment of the invention, a pneumatic device may be used in order to provide an “air bearing” between the rotor and stator. This pneumatic device may be used in combination with a mechanical device. In some embodiments, the mechanical device may be integrated with pneumatic features. Such an embodiment could reduce the wear on the mechanical device by maintaining an “air bearing” like ability to support significant loads without allowing contact, while still retaining the mechanical backup protection. In another embodiment, the pneumatic device can be fitted in the vicinity of the mechanical features noted above in the purely mechanical design. In this embodiment the likelihood of an impact load on the initial contact material pads is minimized, as an air bearing load capacity increases as the clearances are reduced.
The same kind of approach can be used with electromagnetic forces, from an active thrust bearing concept with controllable damping, to an inactive arrangement based on arrays of like polarity magnets facing each other (no damping), to concepts like those used in mag-lev trains that use relative motion between magnet arrays in the train “cars” and specifically shaped coils in the track to levitate the train cars also being selected. These systems have inherent damping that can be “designed” by controlling the resistance of the electrical coils.
Moreover, there are additional designs which use auxiliary windings to the generator windings at other than the generator pole number to establish a controllable axial force over the working area of the rotor and stator. This method requires, like the magnetic thrust bearing, position sensors, power supplies and controls, but affords substantial force generating capacity and control with relatively little extra material (perhaps another layer or two to each 26 layer board), however the added air gap will lower efficiency or require thicker magnets which add cost.
The further object of the invention is inventively achieved by a wind turbine comprising a generator as described above. The wind turbine may include one or many of embodiments described herein. Those of skill in the art will be readily aware that many of the improvements, modifications, and designs provided herein can be combined and modified consistent with the present invention.
In conclusion, the present invention provides, among other things, a system and method for the design, manufacturing and operation of rotating electromagnetic machines—typically called electric motors or electric power generators. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention.
The present application claims priority to commonly owned and assigned provisional application No. 61/350,850, filed Jun. 2, 2010, entitled “Systems and Methods for Improved Direct Drive Generators,” and provisional application No. 61/517,040, filed Apr. 12, 2011, entitled “Air Gap Control System,” both of which are incorporated herein by reference. The present application is related to commonly owned and assigned application no. PCT/US2010/000112, entitled “Segmented Stator for an Axial Field Device,” which is incorporated herein by reference.
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