Composite stator for electromechanical power conversion

A rotating electromechanical apparatus includes a cylindrical ironless stator coil comprising a plurality of wires, a magnetic rotor arranged with the stator coil, wherein the magnetic field flux associated with the rotor interacts with the stator coil wires by electromagnetic induction, a cylindrical bobbin arranged to support the wires, a strand woven on at least the outer circumference of the wire-wrapped cylindrical bobbin, and a curable potting material potting the wires, bobbin and strand to provide an ironless composite stator coil when cured.

BACKGROUND

The present disclosure relates to electromechanical power conversion. More particularly, the disclosure relates to composite stator structures for ironless core motors and generators using Litz wires.

In an aspect of the disclosure, a rotating electromechanical apparatus includes a composite ironless stator coil comprising a plurality of wires, a bobbin arranged to support the Litz wires, and a magnetic rotor arranged with the stator coil, wherein the magnetic field associated with the rotor interacts with the stator coil wires by electromagnetic induction.

In an aspect of the disclosure, a rotating electromechanical apparatus includes a composite ironless stator coil comprising a plurality of wires, a bobbin arranged to support the wires, and a magnetic rotor arranged with the stator coil, wherein the magnetic field associated with the rotor interacts with the stator coil wires by electromagnetic induction.

In an aspect of the disclosure, an ironless stator coil includes a plurality of wires, a planar form arranged as a cylindrical bobbin to support an arrangement of the wires wound around both sides of the planar form, wherein the wire wound planar form is arranged as a cylindrical bobbin, a tape or strand, such as a fiberglass strand, wrapped around either the interior, exterior, or both sides of the wire-wrapped cylinder, and a curable potting material encapsulating the bobbin, the strand and the wires, wherein the potting material, bobbin, strand, and wires form a rigid composite stator structure.

In an aspect of the disclosure, a method of manufacturing an ironless stator coil includes arranging a plurality of Litz wires on a planar form, wherein the Litz wires include braided filaments woven to have a cross-section aspect ratio of width-to-thickness that is greater than one, forming the planar form supporting the Litz wires into a cylindrical bobbin/Litz wire combination on a mandrel, wrapping the cylindrical bobbin/Litz wire combination with a strand or tape, encapsulating the combination with a curable potting material, and curing the potting material to form a rigid composite stator structure.

DETAILED DESCRIPTION

Various concepts will now be presented with reference to a stator for an electric motor or electric power generator.

It is to be understood that the specific order or hierarchy of steps in the methods and processes disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged.

FIG. 1shows a conceptual representation of a stator100of the present disclosure. The stator coil100includes an arrangement of conductors110wound on a cylindrical structure105(a bobbin, described below) in a selected pattern. The conductors may be composed of Litz wire bundles (described below) or of individual wires or conductive metal tape. The stator includes an inner mounting ring (shown on inside diameter of left side of stator), and a phase ring (107). The phase ring107provides means for terminating conductors for multiple phase current induction as an array of magnets in the rotor spins concentrically in proximity to the stator conductor windings. For example, as shown inFIG. 1, the conductors are wound slanted at an angle with respect to the axis of the cylinder. However, other patterns of wire placement on the bobbin are possible.

FIG. 2shows a detail of a single phase of a multiple phase wave winding of a single conductor winding110on a flat form bobbin105, presented in a planar view for illustration. Instantaneous current direction is shown by arrows in the conductor. Referring toFIG. 2, the illustration shows, for example, the two elements of current conductor110(“in” and “out”) at the left front side of the bobbin105, angled from upper left to lower right. The conductor elements are folded over the bobbin105at the lower edge and then are angled from lower left to upper right on the back side of the bobbin105. The winding is continued until the end of the bobbin105is reached, and an interconnector150loops the current path back from the “in” portion of the conductor to the “out” portion. Interconnector150may be a continuous part of the winding, or may be a separate component attached to the conductors110, such as a “buss” bar. Therefore, the winding110as shown inFIG. 2may be a single element, or it may be two elements connected by the interconnector150. In illustrations that follow (e.g.,FIGS. 7, 17, 21-24) it may be understood that the “in” portion and the “out” portion of the conductors110may be provided by the interconnector150as described above, which are shown but not explicitly labeled.

For ease of illustration the conductor winding is shown with only three folds around the bobbin105. The placement of conductor windings and the angle may be referred to as a “wave winding.” Where the conductors on the front and back sides cross opposite each other, the currents are arranged to flow in the same vertical direction, whereas the horizontal directions are opposite. Magnets120on a rotor (not shown) face the stator with alternating north and south poles arranged to face alternating crossings of the front and back side conductors with the same periodicity. With this arrangement, magneto-electro-motive forces produced by relative motion of the rotor and stator100are additive around the common axis of the rotor and stator (when assembled in cylindrical fashion). The symmetric reversal of angles of the conductor elements with respect to the axis of rotation cancels forces parallel to the common axis.

FIG. 3illustrates a portion of the bobbin105and the conductor winding ofFIG. 2, clearly indicating where the conductor110is on one side (in “front”) of the bobbin105, and folds over to the opposite side (in “back”).FIG. 4presents an edge view ofFIG. 3through the line CL-CL′, where it can be seen that the conductor110has a serpentine path wrapped around the bobbin105.

FIG. 5illustrates a comparable winding scheme for a detail of a single phase of a multi-(3) turn three phase “chevron” winding pattern, with alternating pole faces of the rotor magnets520placed opposite the center of each chevron pattern510. A feature of the arrangement of the windings is that the three wires (for a three-phase implementation) cross over each other at only one end of the bobbin505. Thus, there are no wire crossovers anywhere else on the bobbin505, and there is no excess wire extending past the edges of the bobbin505beyond the thickness of the wire bundle. Furthermore, referring to a three-phase arrangement of wire bundles110, there are only six terminations—two for each wire bundle winding—at the opposite end of the length of the bobbin where the crossovers occur. Stators with conventional windings may have excess wire end turns at each end of the wires passing between the magnet poles of a rotor in order to facilitate wire cross-over and reversal of the direction of the wire. In various embodiments, the wire bundle may be an individual wire, a bundle of wires, a Litz wire bundle, a metal tape, or the like.

For a three-phase stator100as an example, the plurality of wire bundles110may be dimensioned and slanted at a diagonal angle to be properly positioned in phase with respect to alternating magnetic flux of the rotor permanent magnets. When the bobbin is formed into a cylindrical structure, as shown inFIG. 1, the axial current reversal of each diagonal leg of a single wire bundle from wire on the outer surface to the same wire bundle on the inner surface also corresponds to a magnetic field reversal, so that the angular forces add circumferentially instead of cancel. Furthermore, by reversing the wire slant angle from the inner surface of the cylindrically arranged bobbin to that of the outer surface, the axial forces due to the crossed field-current vectors are cancelled.

FIG. 6illustrates a comparable winding scheme for a detail of a bobbin605showing a single phase of a multi-(3) turn three phase “lap” winding pattern610, with rotor magnetic pole faces placed opposite the center of each lap pattern. In this embodiment, the sections of conductor parallel to the axis of rotation generate no magneto-electromotive forces parallel to the axis of rotation of relative motion of the rotor and stator.

FIG. 7illustrates the detail of a three phase wave winding relative to rotor magnet pole faces (bobbin not shown) to show the relationship between each phase of wire bundle windings710a,710b,710c, and the magnet poles.

FIG. 8illustrates the equivalent detail of a three phase multi-turn chevron winding. The apparent overlapping of the input of one phase with the output of the adjacent phase occurs on opposite sides of the bobbin (not shown), and do not make contact.

FIG. 9illustrates the equivalent detail of a three phase multi-turn lap winding.

The conductors may be a plurality of Litz wire bundles110, preferably configured, for illustrative purposes as rectangular Litz wire bundles110, as shown inFIGS. 10A and 10B. However, other wire or wire bundle arrangements may be used. Litz wires are advantageously used in motors and generators with coreless stators, due to the reduced eddy current losses in wire filaments of small diameter or cross-section. Additionally, they are more flexible and better adapted to arranging on a stator100than individual wires having the same conductor density as the bundle110. Referring toFIGS. 10A and 10B, individual wire filaments220include a conductor225have an insulation layer230surrounding each conductor225. Rectangular shaped embodiments of wire filaments220have a higher packing fraction than round wire filaments, and thus have a greater conductor density. For illustration, round filaments are shown. The bundle may additionally have an insulating outer layer240surrounding the bundle.

As shown in the photographs ofFIG. 11, in a type-8 Litz wire bundle110, the insulated wire filaments220may be twisted or braided, with an advantage that each filament is subject to the same average magnetic field of a permanent magnet rotor averaged over the bundle length and over time when subjected to relative rotation between the rotor and the stator.

In an embodiment,FIG. 12illustrates the shape of the flat form of the wire bobbin105. Tabs at the end of the long dimension interleave when the bobbin105is curved to form a cylindrical structure.FIG. 13illustrates the bobbin105curved to form a cylinder, and is shown without wires wound on the bobbin105.

FIGS. 14 to 16illustrate various additional embodiments of the bobbin105, shown in flat form.FIG. 14illustrates an embodiment of a bobbin1405for a three phase wave winding pattern of conductors.FIG. 15illustrates an embodiment of a bobbin1505for a three phase chevron winding pattern.FIG. 16illustrates an embodiment of a bobbin1605for a three phase lap winding pattern.

The corresponding wire paths for three phase wave winding, three phase multi-turn chevron winding and three phase multi-turn lap winding are shown inFIGS. 17 to 19, respectively. The chevron winding configuration of the conductors are arranged so that the axial forces described above may be canceled. The lap winding configuration of the conductors are arranged to produce no axial forces, and the angled portions are arranged to cancel axial forces, as described above.

The bobbin105may be formed from a plastic, polymer, laminated, composite or other material, thin enough to be flexibly curved and bent along the greater dimension. Referring toFIG. 12, the bobbin105in flat form has a greater or long dimension (e.g., longitudinal) and a shorter or short dimension, the greater or long dimension being longer than the shorter or short dimension. The edges of the greater dimension have small guide tabs (or alignment pins) to locate and space the wire bundles as they are wound around the bobbin105. Because Litz wire bundles110consist of many smaller wire filaments220that are highly flexible, Litz wire bundles110may be bent around the edge, between the guide tabs (or alignment pins), with a small radius of curvature, thus minimizing any path length to accommodate the reversal of direction from one side of the bobbin110to the other at the edge. However, as described above, other wire types and conductive metallic tapes may be used.

FIG. 20is a photograph of two Litz wire bundles wrapped around the edge of the bobbin. The guiding tabs control the location and spacing of the bundles.

FIG. 21illustrates a perspective view of the flat form of the bobbin105wound with three Litz wire bundles, one for each of a three-phase winding stator100, corresponding to the illustration inFIG. 7. In an embodiment, the Litz (or other type) wires are wound at an angle determined by the short dimension of the bobbin105and the pole pitch, the width of the wire bundles, and the number of phases (e.g., three-phase) that determines the number of wire bundles on the bobbin105. The rotor magnet pole faces may be sized accordingly. Referring toFIG. 21andFIG. 7, it is seen that all electrical connections are made to a pair of first and second wire terminations at the ends of each wire bundle, which for a three-phase winding is six terminations, shown at the left end of the flat form of the bobbin105. Each wire bundle is folded over, as shown at the right end of the flat form of the bobbin105to form a return path to the second termination, and the three wire bundles are interleaved, so that overlapping of the wire bundles occurs only at one end of the flat form of the bobbin105(shown inFIG. 21at the right end) so that the overlapping and path reversal takes place off the edge of the bobbin105, but on the same side of the flat form, as shown, and furthermore, does not take place within the high density magnetic fields between the magnet pole faces on the rotor. With this configuration, therefore, an excess length of wires required to connect between each of the two flat surfaces of the bobbin is kept to a minimum, thereby reducing excess resistance that would occur if turning and overlapping of the wires took place on one side of the bobbin105each time the wires reversed direction.

As indicated above, in a three-phase motor or generator, or other multi-phase electromechanical power converter, there may be three bundles110of wires wound in a 120° phase shifted pattern around the bobbin corresponding to the magnet arrangement on the rotor as described below. Optionally, there may be more than one wire bundle110for each phase.

FIG. 22is an illustration of a first phase of a three phase stator where a multiplicity of wire bundles (e.g., three wire bundles in the figure) wound on the flat form of the bobbin.FIG. 23illustrates the second phase added adjacent to the first phase.FIG. 24illustrates the third phase added adjacent and between the second and first phases. Terminations are shown, for example, at the left upper edge of the bobbin, and the crossover return loops are shown at the upper right edge of the bobbin. In the example illustrated, all wires slanting from upper left to lower right are shown on the front surface of the bobbin, and all wires slanting from lower left to upper right are shown on the back surface of the bobbin, as viewed. The spacing and slant corresponds to the size and spacing of rotor magnet pole faces to provide three phases of induction 120° apart.

Returning toFIG. 1, the cylindrical structure105is configured with a phase ring107which provides electrical connection to each individual bundle110. In a three-phase motor or generator, there may consequently be three individual bundles110, as described above.

FIG. 25illustrates a representative assembly of a rotor300and stator100, such as may be used in an electric motor or an electric generator.

The rotor300may include a single assembly of permanent magnets (not shown) on either an interior or exterior wall of the cylindrical stator100, and may have an assembly of either permanent magnets or field return elements (not shown) facing the opposing wall of the cylindrical structure100.

Referring toFIG. 21, it can be seen that there is substantially no excess wire in end turns at the edges of the bobbin where the wires are wound over from front to back of the planar bobbin. This results in the wire conductors being configurable entirely within the magnetic field flux region of the rotor (with the exception of the cross-over turnarounds at one end of the planar bobbin and the ends of the wire conductors at the other end). It may be appreciated that in such a configuration, the resistivity due to the length of the wire conductors is minimized by the elimination of additional wire required for turnings and crossovers of multiphase wire arrangements each time the wire conductors reach the edges of the bobbin. The absence of such turnings and crossovers reduces the overall volume of the stator as compared to conventional winding arrangements for configuring wires in stators. Furthermore, a larger mass fraction of wire is configured within the magnetic field flux region, thus providing more efficient arrangement of the wire conductors for force induction.

In an embodiment of the disclosure, a method2600of assembling a stator is described with reference toFIG. 26. The method2600of assembly begins at block2610, in which the proper bobbin (e.g., wave, chevron, lap, etc.) is fabricated as a flat form (seeFIG. 12) or in cylindrical form and arranged for wire wrapping. The bobbin may be machined, stamped or cut from suitable material. In block2620a plurality of wires (which may be Litz wires, as shown, or other wires or metal tape), corresponding to the number of multiples per phase and each phase, are wrapped around the bobbin (seeFIG. 21), where the bobbin is arranged flat or in cylindrical form, and with the wires being guided by tabs located at a top and bottom edge of the bobbin (shown in the detail inFIG. 20). The bobbin and wire wrap configuration may be pressed together, with the wires wrapped with a minimum of slack. Preferably, the wires are machine wrapped on the bobbin for uniform tension, flatness and alignment. In block2630a fiber tape or woven cloth may be first wrapped around a cylindrical mandrel before placing the wire wrapped bobbin on the mandrel to form a wire wrapped cylinder. In block2640the wire wrapped bobbin is placed on a cylindrical mandrel, where the mandrel is selected to match the dimensions of the bobbin such that the two ends of the bobbin mate properly so that the angular phase relationship is continuously uniform around the circumference of the now cylindrically arranged bobbin.

In block2650the bobbin wire-coil combination is wrapped with a fiber strand or tape, which may be made, for example, of fiberglass. The tape provides compression of the bobbin-wire coil structure against the surface of the cylindrical mandrel and structural rigidity of the cylindrical wire-wrapped bobbin. In block2660the entire assembly is enclosed in a mold encasing the bobbin and mandrel, leaving an amount of gap on the inner and outer surfaces of the bobbin-wire-fiberglass composite structure for introduction of a curable liquid potting material, which may be an epoxy resin, which is then cured to form a self-supporting composite structure. After curing, the composite structure is ejected from the mandrel (block2670). Mold release compounds, well known in the art of epoxy composite fabrication, may be used to aid in release from the mold and mandrel. In block2680, the phase ring is installed to enable electrical contact to each wire conductor, or wire bundle, and to provide a mating assembly for completing the construction of a motor or generator.

The bobbin may be porous to permit the potting material to substantially infuse around and through the wire bundles110, the wrapping tape and the bobbin, reinforcing the structural rigidity of the stator as a composite structure when cured. The composite construction of the stator may enhance the ability of the stator to withstand turn-to-turn voltage changes and forces generated when subject to electromagnetic induction.

The stator and rotor may then be assembled in additional steps to complete a generator or motor.

FIG. 27illustrates a composite stator in accordance with the method ofFIG. 26. A portion of wire-wrapped cylindrical bobbin is shown (block2640ofFIG. 26). A fiber strand or tape (which may be made of fiberglass) wound on at least one of the inner and outer surfaces of the wire-wrapped cylindrical bobbin (block2650ofFIG. 26). The fiber strand or tape wound around a portion of the at least one wire on the outer surface of the cylindrical bobbin. Potting material pots the wire-wrapped cylindrical bobbin (block2660ofFIG. 26). A portion of the at least one wire is located between the cylindrical bobbin and the potting material.