Low-loss planar winding configuration for axial flux machines

Abstract

The planar stator includes conductive traces forming windings for magnetic poles, and at least first and second conductive paths extending between first and second conductive layers, the first and second conductive paths being positioned radially on a first side of an annular conductive region of an axial flux machine. The conductive traces include a first conductive trace in a first conductive layer and a second conductive trace in a second conductive layer. The first conductive trace includes a first end turn positioned radially on a second side of the annular active region, the second side being opposite to the first side. The second conductive trace includes a second end turn positioned radially on the first side of the annular active region. The first conductive trace extends along a first path, the first path starting at the first conductive path, passing through the first end turn, and ending at the second conductive path. The second conductive trace extends along a second path, the second path starting at the second conductive path and passing through the second end turn. All conductive paths interconnecting the first and second conductive traces are positioned radially on the first side of the annular conductive region.

Description

Background Art

[0001] Several patents describe permanent magnet axial flux motors and generators, including U.S. Patents 7,109,625, 10,170,953, 9,859,763, 10,211,694, and 10,256,690. Summary of the invention

[0002] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features, nor is it intended to limit the scope of the claims incorporated herein.

[0003] In some disclosed embodiments, a stator includes: one or more dielectric substrates adapted to be positioned within an annular active region of an axial flux machine, the axial flux machine including a rotor configured to rotate about an axis of rotation; conductive traces included in at least first and second conductive layers defined by the one or more dielectric substrates, the conductive traces forming windings for magnetic poles of the stator; and at least first and second conductive vias extending between the first and second conductive layers, the first and second conductive vias being positioned radially on a first side of the annular active region. The conductive traces include a first conductive trace in the first conductive layer and a second conductive trace in the second conductive layer. The first conductive trace includes a first end turn positioned radially on a second side of the annular active region, the second side being opposite to the first side. The first conductive trace extends along a first path, the first path starting at the first conductive via, passing through the first end turn, and ending at the second conductive via. The second conductive trace includes a second end turn positioned radially on the first side of the annular active region. The second conductive trace extends along a second path, the second path starting at the second conductive via and passing through the second end turn. The second conductive trace is connected to the first conductive trace through a second conductive path such that the first and second paths are connected in series. All conductive paths interconnecting the first and second conductive traces are positioned radially on a first side of the annular active area.

[0004] In some embodiments, a stator includes: one or more dielectric substrates adapted to be positioned within an annular active region of an axial flux machine, the axial flux machine including a rotor configured to rotate about an axis of rotation; conductive traces included in at least first and second conductive layers defined by the one or more dielectric substrates, the conductive traces forming windings for magnetic poles of the stator; and at least first and second conductive paths extending between the first and second conductive layers, the first and second conductive paths being positioned radially on a first side of the annular active region. The conductive traces include a first conductive trace in the first conductive layer and a second conductive trace in the second conductive layer. The first conductive trace includes a first end turn positioned radially on a second side of the annular active region, the second side being opposite to the first side. The first conductive trace follows a first path, the first path starting at the first conductive path, extending through the first end turn, and ending at the second conductive path. The second conductive trace includes a second end turn positioned radially on a second side of the annular active region. The second conductive trace follows a second path, the second path starting at the first conductive path, extending through the second end turn, and ending at the second conductive path. All conductive pathways interconnecting the first and second conductive traces are positioned radially on a first side of the annular active area. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 shows a partial cutaway perspective view of a stator configured in accordance with the teachings of a prior art patent;

[0006] Figure 2 Shows Figure 1 A top view of the stator is shown;

[0007] Figure 3 The in-gap flux solution for an axial flux machine with alternating pole geometry is shown;

[0008] Figure 4A The components of a particular component of a stator are shown as they are oriented within the stator, the stator containing an internal passageway;

[0009] Figure 4B shows how it would appear if it were unfolded and drawn in a plane Figure 4A , and showing eddy current paths within the structure due to θ-directed magnetic flux;

[0010] Figure 5A shows the assembly of a particular component of a stator according to aspects of the present invention when it is oriented within the stator, wherein the internal passage is omitted;

[0011] Figure 5B shows how it would appear if it were unfolded and drawn in a plane Figure 5A, and showing the eddy current path due to the magnetic flux in the θ direction within the structure;

[0012] Figure 6 A first layer of a stator configured in accordance with certain teachings of the present invention is shown;

[0013] Figure 7 A second layer of a stator configured in accordance with certain teachings of the present invention is shown, the second layer being Figure 6 The first layer shown in is complementary;

[0014] Figure 8 Shows Figure 6 and Figure 7 The stacking of layers in , which shows that by two layers (or multiples of 2), a stator with this construction can be uniformly filled with radial traces;

[0015] Fig. 9 Shows how to Figure 6 and Figure 7 The structure is extended to an actual eighteen-layer stator;

[0016] Fig.10 It shows that the Figure 6 and Figure 7 A complete single-phase connection of sixteen-pole, three-turn windings established by three of the layers shown in , omitting the inner end turns and all other features associated with the other phases;

[0017] Fig.11 Shown in perspective Fig.10 Three layers of

[0018] Fig.12 It is shown in Fig.10 and Fig.11 A first exemplary structure within the stator shown in ; and

[0019] Fig.13 It is shown in Fig.10 and Fig.11 A second exemplary structure within the stator is shown in . DETAILED DESCRIPTION

[0020] Permanent magnet axial flux motors and generators described by several patents (including U.S. Pat. Nos. 7,109,625, 10,170,953, 9,859,763, 10,211,694, and 10,256,690, the entire contents of which are incorporated herein by reference) feature a planar stator assembly (usually a printed circuit board) between rotors that support permanent magnets. Current in the windings in the stator interacts with the magnetic flux density in the gap established by the magnets to produce torque in motor operation. Similarly, when the machine is mechanically driven, it can function as a generator.

[0021] In either mode of operation, the stator of the machine is subjected to a time-varying magnetic flux. The time-varying magnetic flux interacts with the copper in the stator, inducing currents that circulate in loops and copper-filled areas. These effects cause efficiency losses in operation. While most of the flux that causes these losses is axial, i.e., in the z direction, there are auxiliary components in the theta and radial directions. The magnitude of these components varies with the displacement z in the gap.

[0022] The stator configuration disclosed herein is applicable to a planar composite stator and has novel features that mitigate the losses associated with theta-direction flux leakage in a planar stator and provide additional benefits.

[0023] Electric machines of the type described in the above patents generally include a planar stator ("stator") disposed in a gap of a magnetic structure ("rotor") that exhibits a pattern of alternating magnetic poles and corresponding magnetic flux density in the gap. When the stator is powered by an external drive circuit, the interaction of the current in the stator with the magnetic flux in the gap produces a force density in the active area that can cause motion of the rotor. Similarly, when the rotor is set in motion by an external mechanical source, the resulting time-varying magnetic flux captured by the windings causes a voltage on the windings in the stator.

[0024] Abstractly, these main operating modes of the motor depend only on the axial flux established by the magnetic circuit. Therefore, machines of the type presented in the above patents are called "axial flux" machines, and the magnetic circuit in such machines is designed to support flux mainly in the z-direction (i.e., perpendicular to the plane of the stator).

[0025] Figure 1 and Figure 2A partial cutaway perspective view and a top view, respectively, of an example of a stator configured according to the above patent are shown. As shown, the winding structure in the stator of such an axial flux machine is organized to present a radial current density (carried by radial traces 106) to interact with the axial flux. The portion of the stator having such radial features (i.e., the annular region extending between the radial distance r1 (measured from the center point 116 of the stator, which coincides with the axis of rotation of the rotor of the machine) and the radial distance r2 (also measured from the center point 116)) is located in the "active" region of the machine in the sense that it is primarily responsible for generating torque in the machine. The inner and outer radii of the magnets attached to the rotor of the machine are typically located at or near the radial distance r1 (measured from the axis of rotation of the stator) and the radial distance r2 (also measured from the axis of rotation of the stator), respectively, so that an axially directed flux is generated within the annular active region. The remaining features (eg, "end turns" 102, 104 radially adjacent to the annular active area of ​​the stator) exist only for terminals 112 that connect the radial portions in series and parallel combinations and deliver the associated currents and voltages to the machine.

[0026] While the operation of the machine depends on the axial flux in the gap, there are regions throughout the gap where the flux may have significant components in the radial and angular directions. In these, leakage in the theta direction caused by transitions between poles on the rotor may be quite significant and may interact with adjacent radial traces 106. The theta component depends on the spacing of the magnets and its magnitude increases towards the positive and negative z range of the gap. In the center of the gap (radial and axial) and the center of the poles, the flux solution is primarily axial. Figure 3 The in-gap flux solution (described in more detail below) is shown, where a theta-direction leakage flux component 302 within the gap 304 between opposing magnets 306 is apparent.

[0027] The effect of these non-axial components on the performance of the motor or generator arises from their interaction with the stator structure that forms a conductive loop or surface. To explore this mathematically, it is helpful to visualize the "soap film surface" of the loop or conductive structure (this is the surface over which the magnetic flux density can be integrated to find the magnetic flux linked by the conductive structure). When the magnetic flux penetrating the surface is time-varying, a potential is induced in the loop. If the loop is closed, the current will flow with a magnitude related to the resistance of the loop. According to Lenz's Law, the direction of the current can be intuitively understood as the current required to oppose the change in the linked magnetic flux. Specifically, the loop in the stator exposed to the time-varying magnetic flux density establishes currents that attempt to "cancel" the external field. The resulting currents can reduce the current in the motor structure that produces torque; they can interact with any perpendicular components of the magnetic flux to produce resistance depending on the path of the loop; and finally, these currents can combine with the currents associated with the windings to cause unexpectedly high current densities and localized heating in a particular stator structure. In summary, the effect(s) of these trapped leakage flux components is to reduce the efficiency of the machine, increase losses, reduce thermal efficiency, etc. The magnitude of these effects increases in proportion to the operating speed of the machine.

[0028] The main body of the teaching of U.S. Patent No. 7,109,625 ("the '625 patent") is that radial portions of a stator at a specified angle can be connected in parallel at the inner and outer radii by conductive paths or passages. The passages form a conductive path perpendicular to the plane of the stator. For example, Figure 1 and Figure 2 As shown, several groups of radial traces 106 at different angles can be interconnected using inner and outer vias 108, 110. The use of these vias 108, 110 introduces design flexibility to establish connections around the stator. For example, using vias 108, 110, the inner end turns 102 for a particular group of radial traces 106 can be on a different layer than the corresponding outer end turns 104. The vias 108, 110 provide connection points to each radial trace 106 at the inner and outer radius, allowing for the configuration and functional allocation of layers that would not otherwise be feasible. In effect, the vias 108, 110 allow the conductive structures required to form the windings to be allocated to different layers so that they do not interfere.

[0029] In U.S. Patent No. 10,170,953 ("the '953 patent"), a corresponding observation is that functionality on different layers at the outer radius can include heat paths to the outer edge of the stator. Furthermore, these heat paths can include thermal interactions across layers as well as radial heat paths. Figure 1 and Figure 2 , radial thermal paths 114 are evident at the outer edges of the winding structures where they can be effectively coupled to a housing or other heat sink.

[0030] In U.S. Pat. No. 10,256,690 ("the '690 patent"), a structure is disclosed that allows accumulation of turns in the axial as well as theta directions in a planar stator. A key aspect thereof is the construction in which the vias are conductive over a subset of adjacent layers. In the crux of the '690 patent and the embodiments disclosed therein, it is observed that a higher density of inner end turns can be achieved by packing the end turns as closely as possible on each layer. This is in contrast to previous designs in which the inner and outer end turns associated with a given phase are assigned to a particular layer to the exclusion of the inner and outer end turns of other phases. When the inner end turns are assigned at maximum density, there are two unique modes for a three-phase machine. Together, these two modes enable complete connection of the inner end turns in exactly two layers. The winding scheme in the '625 patent supports winding first on turns of adjacent poles and then repeatedly linking pole pairs (i.e., turns first, poles second). Figure 6 An example of a high density inner end turn 602 is shown, which may be used in conjunction with a circuit as described in the '625 patent and in Figure 1 and Figure 2 This is in contrast to the low density end turns shown in FIG.

[0031] Returning to the construction of the '625 patent, reference Figure 1 and Figure 2 , consider a path starting at a single radial trace 106 on the outer radius, continuing radially to the inner radius, following the inner end turn 102 and returning to the outer radius. In plan view, this path is "U" shaped. Several such paths are Figure 4A The illustrated path includes a first set of radial traces 106a extending between the first outer passage 110a and the first inner passage 108a, a set of inner end turns 102 extending between the first inner passage 108a and the second inner passage 108b, and a second set of radial traces 106b extending between the second inner passage 108b and the second outer passage 110b. Figure 1 It may be helpful to visualize the parallel axial displacement layers corresponding to this path, and the result is a "band" of traces punctuated by vias 108, 110. This is Figure 4B is shown in Figure 4A The U-shaped structure 400a has been unfolded and drawn in plane as a corresponding planar structure 400b.

[0032] In the following, the effect of the inter-pole leakage flux 302 is first considered, as in Figure 3 Combination Figure 4B As shown in the "unfolding belt" structure 400b shown in FIG. Figure 4B As shown, the leakage flux 302a to 302d is perpendicular to the "segments" bounded by the paths 108, 110. Figure 4BIn FIG. 1 , the size of the circle representing the leakage flux 302 indicates the relative magnitude of the flux vector shown, and the symbol within the circle indicates the relative direction of the flux vector, where the "X" symbol indicates the flux vector entering the page and the dot symbol indicates the flux vector leaving the page. The passages 108, 110 and radial traces 106 within these segments form a grid, and the eddy currents will respond to the time-varying θ-directed flux integrated over the corresponding segment (ar, z surface) as the rotor rotates.

[0033] λ=∫ A B θ (r,z,θ)dA

[0034] In particular, a given loop in the grid has an induced voltage

[0035]

[0036] in is the rotation speed, and λ indicates the flux linkage in the θ direction. Due to the induced voltage in the loop, there will be a corresponding mesh current determined by the loop resistance.

[0037] The previous expression indicates that the important consideration in this effect (and ignoring here any armature reaction that may occur) is the rate of change of theta of the flux linkage of the loop In addition, due to the magnetic flux leakage B θ (z, θ) at the center of the gap (e.g., at Figure 4B ) is symmetrically reduced to zero, so the mesh current is added to form a branch current (given by Figure 4B 4) will be such that the top and bottom radial traces 106 have a radial pattern along one direction (in Figure 4B to the right in the middle), while the inner trace carries current in the opposite direction (in Figure 4B If the axial flux component is constant as a function of z, the net torque from these circulating currents will be zero. Instead, the current distribution in structure 400b effectively detects the axial flux component B that varies as a function of z. ⊥ (z, θ). In general, the axial flux component is slightly larger at the edge of the stator and decreases toward the center, so the torque opposite to the direction of motion (i.e., the resistance torque) dominates. Importantly, for Figure 4B In the structure 400b shown in FIG. 1 , the left and right radial segments are actually independent due to the passages 108a, 108b at the inner radius. Therefore, the segments produce an eddy current braking effect, which depends on the current in each trace and B ⊥ The speed and locality of the segment when interacting to form the braking torque and B ⊥ changes.

[0038] As mentioned, in Figure 4B The current circulating in the structure 400 having the inner via 108 is indicated by arrow 404. It is mentioned how the inner vias 108a to 108b divide the structure 400 into three regions. Due to the presence of the inner vias 108a to 108b, the three regions are only partially The grid currents cancel to some extent in the solution of the currents in the radial traces 106 of the adjacent loops. In fact, if the θ-directed component of the flux is consistent with z, the cancellation will reduce the innermost current to zero, and the current in the top "track" will be in the opposite direction to the current in the bottom track. However, in the gap 304 (see Figure 3 ), the sign of the θ-direction component changes depending on z. Therefore, the current in the top track is in the same direction as the current in the bottom track. This Figure 4B 4 is indicated by arrow 404. The magnitude of the top and bottom branch currents is greater than the inner current.

[0039] FIG. 5A to FIG. 5B Shows something like Figure 4A - Structure 500 of B, but in which the inner paths 108a to 108b are omitted. In this case, the current (indicated by arrow 504) is determined by the change in the linked net magnetic flux.

[0040] In order to conveniently describe the resistance associated with the current distribution in the stator structure, the inner product is introduced, such as the notation

[0041] τ=k 0 (αB ⊥ )′(γi)=B ⊥ α′γI=kB ⊥ I

[0042] The explanation here is that α (vector) produces B at the z coordinate of the individual traces in the stator structure ⊥ The vector of the (z) components (capturing the z variation of the magnetic flux density in the stator), and γ (vector) produces the current in the individual traces in the grid at the corresponding z value. Therefore, the relative components at each trace depend linearly on the scalar B ⊥ and the induced current at a particular θ and in the positive z range of the stator. Finally, there is a geometric factor k for providing the torque, taking into account the radius at which the corresponding force density occurs 0 The radial flux leakage and armature reaction caused by the current are neglected. In this framework, the focus is on the comparison of the torque contribution depending on the flux linkage in the θ direction and the perpendicular flux density.

[0043] for FIG. 4A to FIG. 4BIn the structure 400, using the notation defined above, the torque is the combined effect of the grid at the first angle (subscript 1) and the grid at the second angle (subscript 2), that is,

[0044] τ a = k(B ⊥1 I 1 +B ⊥1 I 2 )

[0045] Alternatively, rewrite the first loop connected to the first angle λ 1 and the second loop at the second angle λ 2 The term of the θ-dependent magnetic flux at

[0046]

[0047] where r 1 is the first resistor used to calculate the associated current, and r 2 is the second resistance. Note that λ is opposite for the edge of the stator on either side, but results in the same current at the extremes of the stator. To keep the signs consistent for the equations involving the entire structure 400, The term is interpreted as referring to the current in the positive z range of the stator. The Ohmic losses in the structure will be related to

[0048]

[0049] proportional to, where r is the associated resistance.

[0050] consider Figure 3 , for z>0, at either “end” of the structure 400 about τ a Four cases are considered. These cases (transverse rotor pole change movement) are

[0051]

[0052]

[0053]

[0054]

[0055] Here, B ⊥ The >>0 notation indicates that the considered position has a strong axial component, i.e., in the middle of the poles. The weaker inequality indicates transitions between the two poles on either side of the midpoint. For each possible combination, FIG. 4A to FIG. 4B At either end of the structure 400, add to τ aThe component of the torque is negative, i.e., drag. For the two intermediate cases, i.e., for angles close to the transition between poles, the drag will vary as the structure 400 passes through the transition, and most of the drag associated with leakage in the θ direction comes from these interactions. Comparable FIG. 4A to FIG. 4B The term driving this effect in structure 400 is FIG. 5A to FIG. 5B The important items in the structure 500.

[0056] These conditions can occur at either end of the structure 400, and depend in combination on the spacing of the "ends" and the position of the rotors, as follows

[0057]

[0058] In the above table, the notation τ a <0 indicates τ a One of the terms in has a substantial contribution, and t a <<0 indicates that two such resistance terms contribute.

[0059] If FIG. 5A to FIG. 5B If the inner paths 108a-108b are omitted from the structure 500, the structure 500 behaves completely differently. The induced voltage depends on the flux linked by all the "faces" of the structure 500, i.e.,

[0060]

[0061] In the following, for geometric reasons (inner end turns displaced on r), λ from the radial direction 3 The magnetic flux will be negligible due to its small size. Under this assumption, FIG. 4A to FIG. 4B The first expression in structure 400 is equivalent to FIG. 5A to FIG. 5B The resistance term of the structure 500 can be written as

[0062]

[0063] Merge into B ⊥1 and B ⊥2 The manner in which the axial components at the first and second locations are related can be understood by considering the case where they are equal. The end turns force any current induced in the loop to flow in opposite directions at the corresponding locations, resulting in a cancellation of the torque. In addition, there is also a torque from one side of the structure 500 to the other side. possibility of offset.

[0064] As before, interactions can be listed, in this case considering both ends of the structure 500, since the flux linked at one end can now change the resistance at the other end. It should be noted that not all of the following cases are possible in one structure 500 with a given angular separation between radial portions, but these represent all possible combinations. As the rotor turns, a given structure 500 fixed in the stator will have a changing angle relative to the magnetic structure and will transition between the cases listed below. Figure 3 It may help to consider these combinations.

[0065]

[0066] In the table above, the middle four entries show the canceling behavior. These entries correspond to the case where both sides of the structure 500 are in the transition region between the magnetic poles and the coupling θ-directed magnetic flux. 1 ,λ 2 In the case of , there is the possibility of partially offsetting the rate of change of λ as the rotor moves relative to the structure 500. This will occur for the spacing of the traces so that the leakage increases on one side and decreases on the other side, depending on θ. ⊥ In the case of complementarity, there exists a ⊥ In these cases, although the torque based on the induced current can be lower, relatively high current flows. In the four corners of the table, the θ direction loss term is smaller because there is a minimum θ direction flux from either side.

[0067] The eight remaining cases correspond to situations in which one end of the structure 500 experiences significant and the other end is in a region of strong axial flux density. In these cases, The signs change as the rotor moves through the transition, and the corresponding current on the other side of the structure 500 can provide a torque opposite to or in the direction of motion. The negative torque terms associated with these entries exceed the positive torque terms, so the average effect of the adjacent traces in these schemes is drag as the rotor turns. However, the symmetry of the associated terms indicates that the net drag effect is less than the individual drag terms would suggest.

[0068] In summary, the inner path configuration of a typical stator following the teachings of the '625 patent localizes the eddy currents induced by the inter-pole leakage on the rotor. These eddy currents interact with the axial flux component of the magnetic flux to produce drag, and may also produce armature reaction not considered here. If the inner path is removed, these currents are distributed among the radial windings associated with the two poles. In other comparable designs, this can also increase the resistance experienced, and the area over which the leakage flux is integrated to form the EMF in the loop. However, the integration of the magnetic flux on the extended loop formed by the stator without the inner path provides the possibility of offsetting the rate of change of the coupled magnetic flux, lower eddy currents between the poles, and less net drag.

[0069] Finally, it should be noted that the description provided herein is for an "in-runner" type machine in which the shaft is inside the stator. If the machine is of an "outer-runner" configuration, i.e., in which the stator is supported at the inner radius, and phase connections, thermal connections, and the like are placed at the inner radius, then the description provided herein can be similarly reversed. Specifically, the outer end turns in an out-runner configured machine will be similar to the inner end turns described herein, and the passages will be similarly placed at the inner radius and omitted at the outer radius.

[0070] like FIG. 5A to FIG. 5B The development of a stator that eliminates the inner passages 108 in the structure 500 of the '625 patent, but retains the distributed end turns and thermal functions across the layers at the outer radius, continues from consideration of the role of the inner passages 108 in stators of the type described in the '625 patent. Basically, the inner passage configuration provides two functions. First, the radial traces 106 are explicitly connected in parallel, and second, the inner end turns 102 can be placed on any layer and in various multiplicities. The '625 patent discloses a specific distribution of the inner end turns 102, wherein the inner end turns 102 are located on layers associated with a single phase. The necessary condition is to simply form a fully connected winding without conflicting paths that would cause a "short circuit." If the inner passages 108 are omitted, the winding can still be formed, but only with radial traces 106 corresponding to the inner end turns 102 present on a given layer. The radial traces 106 present on two or more layers having the same set of inner end turns 102 are still connected in parallel, but the parallel connection extends from the outer passages 110 at a first angle to the outer passages 110 at a second angle. The radial traces 106 on a given layer that do not have a corresponding inner end turn 102 serve no purpose, so they may be eliminated to reduce eddy current losses due to the axial field component.

[0071] Figure 6An example of a single layer 600 of a stator having a configuration that omits the inner passage 108 as described above is shown. As shown, the layer 600 may include radial traces 606, inner end turns 602, outer end turns 604, and thermal features 608. In the layer 600, each of the radial traces 606 may be connected to a corresponding inner end turn 602, and radial traces 606 without inner end turns 602 may be omitted. The inner end turns 602 may be packed as densely as possible. To ensure Figure 6 The radial traces 606 omitted from the layer 600 in FIG. 1 appear on a different layer, which may have its inner end turns 602 rotated or offset so that they are aligned with the inner end turns 602 of FIG. Figure 6 The inner end turns shown in are complementary. Figure 7 An example of such a complementary layer is shown in (including radial traces 706, inner end turns 702, outer end turns 704, and thermal features 708). Figure 7 Angle α corresponding to the poles on the stator is also shown. Thus, depending on the angle of the rotor, the stator poles can span one or two groups of turns on the layers of the stator shown. At any angle, the rotor can interact evenly with the entire stator because traces at all angles can appear on other layers.

[0072] Figure 8 Provided in Figure 6 and Figure 7 The stacking of layers in , shows that through two layers (or multiples of 2 layers), a stator having this construction can be uniformly filled with radial traces 606, 706. The annular region of the stator shown extending between a first radial distance r1 (measured from a center point 802 of the stator, which coincides with the axis of rotation of the rotor of the machine) and a second radial distance r2 (also measured from the center point 802) can be located in the annular active region of the machine. The inner and outer radii of the magnets attached to the rotor (not shown) of the machine can be located at or near the radial distance r1 (measured from the axis of rotation of the rotor) and the radial distance r2 (also measured from the axis of rotation of the rotor), respectively, thereby generating an axially oriented magnetic flux in the annular active region. Flux density measurements demonstrate that the magnetic flux density in this region is typically greater than about forty percent of the peak axial magnetic flux density in the gap of the machine, while the magnetic flux density outside this region is typically less than forty percent of the peak magnetic flux density in the gap.

[0073] exist Figure 6 and Figure 7 In the embodiment, the outer end turns 604, 704 and the first phase ( Figure 6 ) and the second phase ( Figure 7), thus requiring three layers to achieve a complete set of outer end turns. A complete set of inner end turns 602, 702 can be achieved in two layers. Although the outer end turns 604, 705 can be distributed at a higher density, distributing these connections over at least three layers allows space for thermal features 608, 708, phase connections, and neutral connections. The outer vias 110 allow the thermal, end turn, neutral, and connection structures to be distributed over multiple layers. The outer vias 110 also allow similar layers to be connected in parallel. Fig. 9 This is shown extended to an actual eighteen-layer stator 900. From the outside passage inward, all the layers in the structure correspond in alternating order to Figure 6 or Figure 7 .

[0074] The trajectory of a single phase through the winding scheme described herein is slightly more than that involved for a phase in the planar stator corresponding to the '625 patent. Figures 6 to 9 The same stator as shown in Fig.10 and Fig.11 A complete single-phase connection 1000 is shown, omitting the inner end turns 602, 702 and all other features associated with the other phases. Fig.11 It is shown that the winding can be distributed over three layers due to the choice of allocation of the outer end turns 604. There are only two unique organizations of radial traces 606, 706 and inner end turns 602, 702 within the radius of the passage 110, one of which appears in the illustrated structure with a multiplicity of two (i.e., in Fig.11 on the top and middle layers as shown in ). Fig.11 , the external functionality is split between the outer end turns 604 and the thermal features 608, 708. If the thermal features 608, 708 are omitted, the complete stator can be made into only two layers (e.g., Fig.11 top and bottom layers shown in ).

[0075] The arrangement of the windings described herein has several advantages over the windings described previously. First, at high speeds, the eddy current losses in the stator are reduced relative to stators of conventional design. This facilitates loss-related trade-offs to achieve higher efficiency, higher speed operation at a given efficiency level, etc. Second, the losses that persist in the design described herein are moved from the inner radius to the outer radius of the machine relative to stators of conventional construction. For example, there are no losses in the circulating currents in the inner radius passage 108. Third, when manufacturing the stator, the inner passage 108 is typically "drilled" in an operation separate from the manufacture of the traces. This requires aligning and precisely positioning the layers of the planar stator for drilling. In practice, this means that copper voids are required around the inner passage. This limits the minimum spacing between features at the inner radius, which controls the number and combination of radial features that can be accommodated within a given overall size. In other words, higher trace densities are typically possible on stators without inner passages 108 compared to stators of conventional design.

[0076] The design described herein has allowed the construction of machines that operate efficiently at over 20000 rpm. Similarly, it has allowed the construction of machines with a diameter of less than 2 cm.

[0077] Figure 1 A partial cutaway perspective view of the layers of a stator 100 designed according to the '625 patent is shown, with the functionality of inner end turns 102 and outer end turns 104 distributed over multiple layers. Radial traces 106 are connected in parallel by both inner and outer passages 108, 110 on all layers.

[0078] Figure 2 Shows Figure 1 A single layer of the stator 100. Passageway ( Figure 1 ) allows radial traces 106 that are not connected by inner end turns 102 or outer end turns 104 on a particular layer to be connected in parallel, thereby contributing to a reduced resistance of the radial traces 106.

[0079] Figure 3 Numerical solutions for the air gap flux density for a particular geometry are shown. In particular, Figure 3 represents the segments along the z and theta directions at constant r. The major components include the magnet 306, the back iron 308 and the major axial solution in the gap 304 between the magnets 306 of opposite polarity. The flux leakage between the poles shows a theta direction component 302 that can interact with the stator features and cause losses.

[0080] Figure 4A It is shown that in Figure 1 The generally U-shaped structure 400a within a conventional stator is shown in the structure. The vertical axis is exaggerated for clarity.

[0081] Figure 4B Shown Figure 4A The planar structure 400b shows how the U-shaped structure 400a would appear if it were unfolded and drawn in a plane. Figure 4A , the vertical axis is exaggerated for clarity. Figure 4B The current distribution driven in a pair of radial traces 106a, 106b connected by the inner end turn 102 is shown. As shown, the overall structure starts at the outer path 110a, proceeds along the first set of radial traces 106a, encounters the first inner path 108a, crosses a set of inner end turns 102, encounters the second inner path 108b, proceeds along the second set of radial traces 106b, and ends at the second outer path 110b. The structure includes multiple layers as shown, and is nominally Figure 3 The gap 304 indicated in FIG. is the center. When the structure encounters leakage flux 302 ( Figure 3 and as shown in Figure 4), it is Figure 4B The current indicated by arrow 404 responds. Figure 4B Schematically indicates how the leakage flux 302a to 302d linked by the windows of the structure decreases as the offset from the centerline of the gap decreases. For clarity, the response current indicated by arrow 404 is only Figure 4B The right hand side of is shown as being linked to the flux in that portion of the structure 400. Any response in the rest of the structure 400 will be linked to the flux in those locations and will be independent of the response current 404 due to the pathways 108a, 108b.

[0082] Figure 5A A generally U-shaped structure 500a similar to the generally U-shaped structure 500a is shown, but with the inner passages 108a, 108b omitted. The vertical axis is exaggerated for clarity.

[0083] Figure 5B Shown Figure 5A The planar structure 500b of how the U-shaped structure 500a will appear when unfolded and drawn in a plane. Figure 5A , the vertical axis is exaggerated for clarity. Figure 5B The current response (indicated by arrow 504) of this structure to an applied time rate of change of leakage flux 302 is shown. As shown, the response current flows in both sides of structure 500.

[0084] Figure 6 The first layer 600 of the stator is shown where the inner end turns 602 are present at the highest possible density and only radial traces 606 corresponding to the inner end turns 602 are present on the layer. Since there are no radial traces 606 on this layer that need to be linked by inner end turns on another layer, there is no need for inner vias 108. The outer end turns 604 on the layer 600 terminate in the outer vias 110, whether or not corresponding radial traces 606 are present on that layer.

[0085] Figure 7 Shows Figure 6 700 of the stator shown in FIG. As shown, the inner end turns 702 and associated radial traces 706 are Figure 6 The inner end turns 602 and radial traces 606 shown in FIG. 6 are complementary.

[0086] Figure 8 Shows Figure 6 The layers 600 and Figure 7 800 of layer 700 is shown in which layer 600 is emphasized and layer 700 is obscured. Figure 8 The inner end turns 602, 702 and radial traces 606, 706 from individual layers are shown together to provide a complete set of radial traces and inner end turns on both layers.

[0087] Fig. 9 The assembly and combination of several layers are shown, wherein the inner end turns 602, 702 and radial traces 606, 706 follow Figure 8 The pattern established in , and external vias 110 are used to distribute end turns, thermal and connection features over multiple layers.

[0088] Fig.10 It shows that the superposition image Figure 6 and Figure 7 1000, omitting the inner end turns 602, 702 and all other features associated with the other phases. The path shown begins at phase connection 1002 and includes radial traces 606a, 606b, 706a, 706b, inner end turns 602, 702, outer end turns 604a, 604b, and outer via 110. As shown, a portion of a neutral point connection 1004 may connect the phase shown to other phases to form a neutral point. Fig.10 All features in can be placed on a single layer, especially if similar features in other phases are considered.

[0089] Fig.11 Shown in perspective Fig.10 of three layers. Fig.10 The single phase of Figure 6 and Figure 7 1004. The two types of layers 600 and 700 shown in FIG. 1000 are supported. In the example shown, one of those types of layers is used in both the top and middle layers in the stack, and the other type of layer is used in the bottom layer. The outer end turns 604 of the phase appear on the top layer. The thermal features of the phase appear on the bottom layer where they do not interfere with the end turns of another phase. The power connector 1002 is also on the bottom layer. The middle layer includes a neutral point connection 1004.

[0090] Fig.12 and Fig.13 The first exemplary structure 1200 and the second exemplary structure 1300 are shown respectively, which are embodied in Fig.10 and Fig.11 1000 and can provide various performance advantages for an axial flux machine as outlined herein. In this regard, it should be understood that structures 1200, 1300 can have applicability and provide similar advantages to structures other than stator 1000. Therefore, Fig.10 and Fig.11 Additional features and / or nuances of the specific configurations shown should not be considered limiting.

[0091] First reference Fig.12 , the radial traces 706a, 706b and the inner end turn 702a may be included in a first conductive layer, and the outer end turn 604a may be included in a second conductive layer. Although not specifically shown, it should be understood that the structure 1200 may additionally include one or more dielectric substrates supporting these conductive layers. These dielectric substrates may be suitable for being positioned within an annular active region of an axial flux machine that includes a rotor configured to rotate about an axis of rotation. As described above, the annular portion of the stator in which the radial traces 706a, 706b are disposed may be positioned within the "active" region of the machine, as the "active" region is the region primarily responsible for the generation of torque in the machine.

[0092] like Fig.12 As shown in , structure 1200 may also include at least a first conductive path 110a and a second conductive path 110c extending between the first and second conductive layers. The first conductive path 110a and the second conductive path 110d may be positioned to be radially located on the first side of the annular active area. In some embodiments, additional conductive paths 110b, 110d may also extend between the first and second conductive layers (e.g., parallel to the first and second conductive paths 110a, 110c, respectively) and may also be positioned to be radially located on the first side of the annular active area. Radial traces 706a, 706b and inner end turn 702a may together form a first conductive trace in the first conductive layer. The inner end turn 702a may be positioned to be radially located on the second side of the annular active area, the second side being opposite to the first side. As shown, the first conductive trace may extend along a first path that starts at the first conductive path 110a, passes through the inner end turn 702a, and ends at the second conductive path 110c.

[0093] The outer end turn 604a may form a second conductive trace in the second conductive layer. The outer end turn 604a may be positioned radially on a first side of the annular active area. As shown, the second conductive trace may extend along a second path that begins at the second conductive path 110c and passes through the outer end turn 604a. The second conductive trace (e.g., including the outer end turn 604a) may be connected to the first conductive trace (e.g., including radial traces 706a, 706b and the inner end turn 702) through the second conductive path 110c, such that the first and second paths are connected in series. In some embodiments, the second conductive trace (e.g., including the outer end turn 604a) may terminate on an additional conductive path ( Fig.12 ), the additional conductive path may extend between the first and second conductive layers and be positioned radially on the first side of the annular active area, thereby enabling a connection from the additional conductive path to another radial trace ( Fig.12 The location of such additional conductive paths may depend on whether the stator windings are arranged in a serpentine pattern or a coil pattern.

[0094] like Fig.12 As can be seen in the structure 1200, all conductive pathways interconnecting the first conductive traces (e.g., including radial traces 706a, 706b and inner end turn 702) and the second conductive traces (e.g., including outer end turn 604a) are positioned radially on the first side of the annular active area. Omitting conductive pathways on the second side of the annular active area and at other locations can provide a number of advantages, such as reducing losses due to eddy currents caused by the θ-directed magnetic flux, as outlined above.

[0095] Next reference Fig.13 , radial traces 606c, 606d and inner end turn 602a may be included in a first conductive layer, and radial traces 606e, 606f and inner end turn 602b may be included in a second conductive layer. Although not specifically shown, it should be understood that structure 1300 may additionally include one or more dielectric substrates supporting these conductive layers. These dielectric substrates may be adapted to be positioned within an annular active region of an axial flux machine that includes a rotor configured to rotate about an axis of rotation. As described above, the annular portion of the stator in which radial traces 606c, 606d, 606e, 606f are disposed may be positioned within the "active" region of the machine because the "active" region is the region primarily responsible for the generation of torque in the machine.

[0096] like Fig.13As shown in , structure 1300 may also include at least a first conductive path 110e and a second conductive path 110g extending between the first and second conductive layers. The first conductive path 110e and the second conductive path 110g may be positioned radially on the first side of the annular active area. In some embodiments, additional conductive paths 110f, 110h may also extend between the first and second conductive layers (e.g., parallel to the first and second conductive paths 110e, 110g, respectively) and may also be positioned radially on the first side of the annular active area.

[0097] The radial traces 606c, 606d and the inner end turn 602a may together form a first conductive trace in the first conductive layer. The inner end turn 602a may be positioned radially on a second side of the annular active area, the second side being opposite to the first side. As shown, the first conductive trace may extend along a first path that starts at the first conductive path 110e, passes through the inner end turn 602a, and ends at the second conductive path 110g. Similarly, the radial traces 606e, 606f and the inner end turn 602b may together form a second conductive trace in the second conductive layer. The inner end turn 602b may be positioned radially on a second side of the annular active area. As shown, the second conductive trace may extend along a second path that starts at the first conductive path 110e, passes through the inner end turn 602b, and ends at the second conductive path 110g.

[0098] like Fig.13 As can be seen in the structure 1300, all conductive pathways interconnecting the first conductive traces (e.g., including radial traces 606c, 606d and inner end turn 602a) and the second conductive traces (e.g., including radial traces 606e, 606f and inner end turn 602b) are positioned radially on the first side of the annular active area. Omitting conductive pathways on the second side of the annular active area and other locations can provide a number of advantages, such as reducing losses due to eddy currents caused by the θ-directed magnetic flux, as outlined above.

[0099] Thus, having described several aspects of at least one embodiment, it should be appreciated that various changes, modifications and improvements will readily occur to those skilled in the art. Such changes, modifications and improvements are intended to be part of the present invention and are intended to be within the spirit and scope of the present invention. Therefore, the foregoing description and drawings are intended only as examples.

[0100] The various aspects of the present invention may be used individually, in combination, or in a variety of arrangements not specifically discussed in the embodiments described hereinabove, and are therefore not limited in this application to the details and configurations of the components described in the foregoing description or shown in the accompanying drawings. For example, the aspects described in one embodiment may be combined in any manner with the aspects described in other embodiments.

[0101] Furthermore, the disclosed aspects may be embodied as a method, and examples of such methods have been provided. The actions performed as part of the method may be ordered in any suitable manner. Thus, embodiments may be constructed in which the actions are performed in an order different from that shown, which may include performing some actions simultaneously, even though shown as sequential actions in illustrative embodiments.

[0102] The use of ordinal terms such as "first", "second", "third", etc. in the claims to modify claim components does not itself imply any priority, precedence or order of one claim component over another or the temporal order of the actions of performing a method, but is merely used as a marker to distinguish a claimed component with a particular name from another component with the same name (but using an ordinal term) to distinguish the claim components.

[0103] Furthermore, the phrases and terms used herein are for descriptive purposes and should not be considered limiting. The use of "comprising," "including," or "having," "containing," "involving," and variations thereof herein is intended to encompass the items listed thereafter and their equivalents as well as additional items.

Claims

1. A planar stator, comprising: one or more dielectric substrates adapted to be positioned within an annular active region of an axial flux machine including a rotor configured to rotate about an axis of rotation; Conductive traces contained in at least first and second conductive layers defined by one or more dielectric substrates, the conductive traces forming windings for magnetic poles of the stator; and at least first and second conductive pathways extending between and interconnecting portions of the conductive traces in the first and second conductive layers, the first and second conductive pathways being positioned radially on a first side of the annular active area; in: The conductive trace comprises a first conductive trace in a first conductive layer, The first conductive trace includes a first end turn positioned radially on a second side of the annular active area, the second side being opposite to the first side, The first conductive trace extends along a first path that begins at a first conductive via, passes through a first end turn, and ends at a second conductive via, The conductive trace comprises a second conductive trace in a second conductive layer, the second conductive trace comprising a second end turn positioned radially on a first side of the annular active area, The second conductive trace extends along a second path that begins at the second conductive via and passes through the second end turn, The second conductive trace is connected to the first conductive trace through a second conductive path such that the first and second paths are connected in series, and All conductive pathways interconnecting the first and second conductive traces are positioned radially on a first side of the annular active area.

2. The planar stator according to claim 1, further comprising: A third conductive pathway extends between the first and second conductive layers and is positioned radially on the first side of the annular active area, wherein a second path along which the second conductive trace extends begins at the second conductive pathway, passes through the second end turn, and ends at the third conductive pathway. 3 . The planar stator of claim 2 , wherein the third conductive path is positioned such that the first conductive trace and the second conductive trace form part of a serpentine winding.

4. The planar stator of claim 2, wherein the third conductive path is positioned such that the first conductive trace and the second conductive trace form part of a spiral winding.

5. The planar stator according to claim 2, further comprising: a fourth conductive path extending between the first and second conductive layers and positioned radially on a first side of the annular active area; and A third conductive trace in the second conductive layer, the third conductive trace including a third end turn positioned radially on a second side of the annular active area, wherein the third conductive trace extends along a third path, the third path starting at the third conductive via, passing through the third end turn, and ending at a fourth conductive via.

6. The planar stator of claim 5, wherein the one or more dielectric substrates further define a third conductive layer, the third conductive path extending through the third conductive layer, and the stator further comprises: A fourth conductive trace in the third conductive layer, the fourth conductive trace including a fourth end turn positioned radially on a second side of the annular active area, wherein the fourth conductive trace extends along a fourth path, the fourth path starting at the third conductive via, passing through the fourth end turn, and ending at the fourth conductive via.

7. The planar stator according to claim 6, wherein: All conductive pathways interconnecting the third and fourth conductive traces are positioned radially on a first side of the annular active area.

8. The planar stator of claim 1, further comprising an additional via extending between the first and second conductive layers and positioned radially on the first side of the annular active area, wherein the second conductive trace is further connected to the first conductive trace through the additional conductive via.

9. The planar stator of claim 1, wherein the first end turn is an inner end turn and the second end turn is an outer end turn.

10. The planar stator of claim 1, wherein the first end turn is an outer end turn and the second end turn is an inner end turn.

11. An axial flux motor or generator comprising a planar stator according to claim 1.

12. A planar stator, comprising: one or more dielectric substrates adapted to be positioned within an annular active region of an axial flux machine including a rotor configured to rotate about an axis of rotation; Conductive traces contained in at least first and second conductive layers defined by one or more dielectric substrates, the conductive traces forming windings for magnetic poles of the stator; and at least first and second conductive pathways extending between the first and second conductive layers, the first and second conductive pathways being positioned radially on a first side of the annular active area; in: The conductive trace comprises a first conductive trace in a first conductive layer, The first conductive trace includes a first end turn positioned radially on a second side of the annular active area, the second side being opposite to the first side, The first conductive trace follows a first path that begins at a first conductive via, extends through a first end turn, and ends at a second conductive via, The conductive trace comprises a second conductive trace in a second conductive layer, the second conductive trace comprising a second end turn positioned radially on a second side of the annular active area, The second conductive trace follows a second path that begins at the first conductive via, extends through the second end turn, and ends at the second conductive via, and All conductive pathways interconnecting the first and second conductive traces are positioned radially on a first side of the annular active area.

13. The planar stator of claim 12, wherein the first path has the same size and shape as the second path.

14. The planar stator of claim 12, wherein the first and second end turns are inner end turns.

15. The planar stator of claim 12, wherein the first and second end turns are outer end turns.

16. The planar stator according to claim 12, further comprising: a third conductive path extending between the first and second conductive layers, the third conductive path being positioned radially on a first side of the annular active area; and A third conductive trace in the second conductive layer, the third conductive trace including a third end turn positioned radially on the first side of the annular active area, wherein the third conductive trace extends along a third path, the third path starting at the second conductive pathway, passing through the third end turn, and ending at the third conductive pathway.

17. The planar stator of claim 16, wherein the one or more dielectric substrates further define a third conductive layer, the third conductive path extending through the third conductive layer, and the stator further comprises: a fourth conductive path extending through the first, second and third conductive layers, the fourth conductive path being positioned radially on a first side of the annular active area; and A fourth conductive trace in the third conductive layer, the fourth conductive trace including a fourth end turn positioned radially on a second side of the annular active area, wherein the fourth conductive trace extends along a fourth path, the fourth path starting at the third conductive via, passing through the fourth end turn, and ending at the fourth conductive via.

18. An axial flux motor or generator comprising a planar stator according to claim 12.

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