Planar stator configurations for axial flux machines.

Abstract

In some embodiments, two or more different types of stator structures may be disposed within the gap of an axial flux machine. Such an arrangement may be advantageous to produce a machine optimized for multiple modes of operation, such as, for example, generation of mechanical torque, conversion of mechanical torque to electrical power, and / or dissipation of mechanical power. Additionally, in some embodiments, an axial flux machine may include a planar stator having windings arranged to be positioned within an active area of ​​the machine, and may further include at least one switch configured to be selectively closed to establish an electrical connection between individual ends of the windings at times when the windings are not coupled to an external power source.

Description

[Background technology]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 150,129, filed on February 17, 2021, and entitled “MULTI-STATOR AXIAL FLUX MACHINE.”

[0002] Axial flux motors and generators described in several patents, including U.S. Pat. No. 7,109,625 ("the '625 patent"), the entire contents of which are incorporated herein by reference, feature a planar printed circuit board stator assembly interposed between a rotor assembly supporting magnets with alternating north and south poles. The magnetic flux between the magnets interacts with current densities supported by wiring in the printed circuit stator to produce torque.

[0003] This type of electric machine can operate as either a motor or a generator and has several useful properties, including that the torque as a function of angle is smooth and capable of possessing high quality motion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 7,109,625 Summary of the Invention [Means for solving the problem]

[0005] 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 or essential features, nor is it intended to limit the scope of the claims included herewith.

[0006] In some of the disclosed embodiments, a planar stator for an axial flux machine (having a rotor including one or more magnets that generate a first magnetic flux generally parallel to the axis of rotation of the rotor within an active area in a gap of the axial flux machine) comprises at least first, second, third, and fourth terminals, each adapted to be connected to a circuitry external to the planar stator, and at least one first winding arranged to be positioned within the active area, the at least one first winding having first and second ends electrically connected to the first and second terminals, respectively, and a first and at least one first winding, wherein an electrical characteristic between the first terminal and the second terminal as measured when the second terminal is not connected to a circuit network has a first value; and at least one second winding arranged to be positioned within the active area, the at least one second winding being electrically isolated from the at least one first winding and having third and fourth ends electrically connected to the third and fourth terminals, respectively, wherein the electrical characteristic between the third terminal and the fourth terminal as measured when the third and fourth terminals are not connected to a circuit network has a second value that is substantially different from the first value.

[0007] In some embodiments, a planar stator for an axial flux machine (having a rotor including one or more magnets that generate a first magnetic flux generally parallel to the axis of rotation of the rotor within an active area in a gap of the axial flux machine) comprises a first conductive sheet arranged to be positioned within the active area such that generation of eddy currents in the first conductive sheet imposes a drag force on the rotor, and at least a first winding arranged to be positioned within the active area, the first winding having at least first and second terminals electrically connected to respective ends of the first winding.

[0008] In some embodiments, a planar stator for an axial flux machine (having a rotor including one or more magnets that generate a first magnetic flux generally parallel to the axis of rotation of the rotor within an active area in a gap of the axial flux machine) comprises at least a first winding arranged to be positioned within the active area, the first winding having at least first and second terminals electrically connected to respective ends of the first winding, and at least one switch configured to be selectively closed to establish an electrical connection between the first terminal and the second terminal at times when the first winding is not coupled to an external power source. [Brief description of the drawings]

[0009] Objects, aspects, features, and advantages of the embodiments disclosed herein will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numbers identify similar or identical elements. In connection with the figures, reference numbers introduced herein may be repeated in one or more subsequent figures without additional description within the specification to provide context for other features, and all elements may not be labeled in all figures. The drawings are not necessarily to scale, with emphasis instead being placed on illustrating embodiments, principles, and concepts. The drawings are not intended to limit the scope of the claims contained herein.

[0010] [Figure 1] FIG. 1 shows an exploded view of the internal components of an exemplary axial flux machine with a planar stator.

[0011] [Diagram 2] FIG. 2 shows a cross-sectional view of an axial flux machine including the components shown in FIG.

[0012] [Diagram 3] FIG. 3 shows a variation of an axial flux machine that includes a planar stator section.

[0013] [Figure 4] FIG. 4 illustrates an exploded view of the internal components of an example axial flux machine with a planar stator, constructed in accordance with certain embodiments of the present disclosure.

[0014] [Diagram 5] FIG. 5 shows a cross-sectional view of an axial flux machine including the components shown in FIG.

[0015] [Figure 6] FIG. 6 shows a perspective view of the axial flux machine shown in FIGS. 4 and 5, with the shaft and upper rotor assembly removed so that the orientation of the individual section types can be clearly seen.

[0016] [Figure 7] FIG. 7 illustrates a first exemplary implementation of a planar axial flux machine that includes several different stator construction types.

[0017] [Figure 8A] FIG. 8A illustrates a first possible scheme for driving (or receiving power from) the three windings via multiple terminals.

[0018] [Figure 8B] FIG. 8B illustrates a first possible scheme for driving (or receiving power from) the three windings via multiple terminals.

[0019] [Figure 8C] FIG. 8C illustrates a first possible scheme for driving (or receiving power from) the three windings via multiple terminals.

[0020] [Figure 9] FIG. 9 illustrates a second exemplary implementation of a planar axial flux machine that includes several different stator construction types.

[0021] [Figure 10] FIG. 10 illustrates a third exemplary implementation of a planar axial flux machine that includes several different stator construction types.

[0022] [Figure 11] FIG. 11 shows an example of a planar axial flux machine having a novel cellular configuration that may be employed either alone or with one or more additional or different cellular structures.

[0023] [Figure 12] FIG. 12 illustrates a fourth exemplary implementation of a planar axial flux machine that includes a number of different stator construction types.

[0024] [Figure 13] FIG. 13 illustrates a fifth exemplary implementation of a planar axial flux machine that includes a number of different stator construction types.

[0025] [Figure 14] FIG. 14 illustrates a sixth exemplary implementation of a planar axial flux machine that includes a number of different stator construction types. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Detailed Description Variations of the machine described in the '625 patent use stators that do not describe a complete circle. In particular, one or more planar stator sections, fabricated using printed circuit board (PCB) machining or similar techniques, may be placed in the gap between the rotors. This type of machine is described in U.S. Patent Application Publication No. 2020 / 067361 ("the '361 publication"), the entire contents of which are incorporated herein by reference, and may support angle-dependent torque requirements. In these types of applications, the portion of the rotor that is densely populated with magnets is aligned with the stator section at the angle for which maximum torque is required. Also discussed in the '361 publication is the possibility of a machine similar to the rotor in the '625 patent in the sense that the stator includes one or more sections, but the rotor is uniformly populated with magnetic poles. Machines similar to those described in the '625 patent can be made by assembling complete annular rings from sections, as opposed to making the machine from a monolithic circuit board.

[0027] Disclosed herein are, among other things, axial flux electric machines incorporating multiple stator structures disposed within the gap between rotors, in which at least two of the stator structures have different functions (including the possibility that one of the structures is a conductive sheet that introduces eddy current damping but cannot produce motor action or operate as a generator). Such configurations may result in electric machines with thermal, electrical, and mechanical properties that cannot be achieved with a single stator structure or multiple identical stator structures. In some implementations, such functionality may be achieved by placing separate stator sections at different angular positions relative to the machine's axis of rotation within the gap. In other implementations, different stator structures may be arranged to overlap, at least in part, with one another within the gap, such as by placing separate stator structures on different layers of the same printed circuit board.

[0028] The inventors also recognize and appreciate that certain of the stator structures disclosed herein and / or the external circuitry associated with those structures are novel in their own right and, when employed within an axial flux machine, enable new and advantageous functionality to be achieved. Thus, as explained in more detail below, certain of the novel stator structures disclosed herein need not be employed in conjunction with one or more other types of stator structures in accordance with some embodiments.

[0029] 1 and 2 show exploded and cross-sectional views, respectively, of a planar stator axial flux machine 100. As shown in these figures, a planar stator 102 may be placed in the gap of a magnetic circuit established by rotor components. As best shown in FIG. 1, the rotor may include magnets 104a, 104b and support structures 106a, 106b that together form paired rotor assemblies 108a, 108b that may be attached to a rotor shaft 110. As shown in FIG. 2, an outer edge 112 of the stator 102 may be fixedly secured to a housing 114 (e.g., by being held between respective sections 114a and 114b of the housing 114), while a rotor shaft 110 (to which the rotor assemblies 108a, 108b are attached) may be rotatable relative to the housing 114 (e.g., via bearings 116).

[0030] In motor mode, a current density can be imposed on the stator 102 by the controller 118 (shown in FIG. 1 ), which rotates synchronously about the rotor's axis of rotation. The interaction of this current density with the magnetic flux in the gap from the rotor assemblies 108a, 108b leads to a torque of electromagnetic origin. The controller 118 can be operated such that the energy conversion provided by this structure is bidirectional, in the sense that the electric machine can absorb power from the mechanical terminals and deliver it to the electrical terminals, or it can deliver power to the mechanical terminals. Under appropriate control, this kind of machine can simulate various mechanical loads, including components of friction, moments of inertia, and the like.

[0031] 3 shows a variation of a planar axial flux machine in which the stator is not a torus, but a section 302. There may be various advantages to producing the stator in this manner, identified in the '361 publication, including that the machine may be designed for greater manufacturing efficiency and / or suitable for loads that are periodic in nature. This may be advantageous, especially when the radius of the machine is large.

[0032] As mentioned above, in accordance with some aspects of the disclosure, two or more different types of stator structures may be disposed within the gap of an axial flux machine, such as the above-described planar axial flux machine 100. Such an arrangement may be advantageous to produce a machine optimized for multiple modes of operation, such as, for example, generation of mechanical torque, conversion of mechanical torque to electrical power, and / or dissipation of mechanical power.

[0033] 4 and 5 show exploded and cross-sectional views, respectively, of one possible structure of such a planar axial flux machine 400. In the illustrated example, the machine 400 includes four stator sections 402a, 402b, 404a, 404b that are angularly offset from one another relative to the rotor's axis of rotation. In other implementations, the machine 400 may instead have additional or fewer sections.

[0034] 6 shows a perspective view of the machine 400 shown in FIGS. 4 and 5, with the shaft 110 and upper rotor assembly 108a removed so that the orientation of the individual compartment types can be clearly seen. In some implementations, two of the compartments (e.g., compartments 402a and 402b) may be type "A" and two of the compartments (e.g., compartments 404a and 404b) may be type "B," as indicated by the labeling on the individual compartments 402a, 402b, 404a, 404b in FIGS. 4 and 6. In other implementations, different quantities of the individual compartment types may be provided and / or additional compartment types (e.g., one or more type "C" compartments) may be employed along with other compartment types. For example, in some implementations, machine 400 may instead be configured with (1) three sections of type "A" and one section of type "B", (2) two sections of type "B" and one section of type "A", (3) one section of type "A" and one section of type "B", (4) two sections of type "A", one section of type "B", and one section of type "C", etc. As can also be seen in FIGS. 4-6 , certain types of sections may include one or more terminals 406 configured to enable connection between conductive wiring on the section (e.g., conductive wiring forming one or more windings) and circuitry external to the section. Examples of particular types of sections that may include such terminals 406 are described below.

[0035] In some implementations, the poles of the magnets 104a, 104b of the machine 400 may be uniformly distributed about the rotor's axis of rotation, as in the case of the machine 100 shown in Figures 1 and 2. In other implementations, the poles of the magnets 104a, 104b of the machine 400 may be non-uniformly distributed about the rotor's axis of rotation, as in the case of the machine 300 shown in Figure 3.

[0036] FIG. 7 illustrates a first exemplary implementation of a planar axial flux machine 700 including a number of different stator construction types, as described in connection with FIGS. 4-6. As with FIG. 6, the upper rotor assembly 108a is not depicted in FIG. 7 to allow for a clearer view of the two exemplary stator sections 702, 704 included within the machine 700. Although only two stator sections 702, 704 are shown in FIG. 7, as previously mentioned, it should be understood that one or more additional stator sections of either or both of the types illustrated, and / or one or more additional sections of a different type (such as those described herein) may be employed in other implementations.

[0037] 7, section 702 and section 704 may each include one or more windings 706. In some implementations, the windings 706 in section 702 may be electrically isolated from and have substantially different electrical properties than the windings 706 in section 704. In the illustrated embodiment, for example, section 702 includes windings 706a, 706b, and 706c for three separate phases, with such windings per phase forming a total of four turns, while section 704 includes windings 706d, 706e, and 706f for three separate phases, with such windings per phase forming a total of two turns.

[0038] In embodiments where the windings 706a, 706b, 706c of the section 702 are connected to the terminals 406a, 406b, 406c using a "Y" configuration (e.g., the diagram shown in FIG. 8A), two of the windings 706 will be identified between each individual pair of terminals 406a, 406b, 406c. In embodiments where the windings 706a, 706b, 706c of the section 702 are connected to the terminals 406a, 406b, 406c using a "Δ" configuration (e.g., the diagram shown in FIG. 8B), each individual pair of terminals 406a, 406b, 406c will identify one winding 706 connected in parallel in combination with two other windings 706 connected in series. In an embodiment in which the windings 706a, 706b, 706c of the section 702 are connected to three separate pairs of terminals (e.g., the diagram depicted in FIG. 8C ), each individual pair of terminals 406a, 406b, 406c will identify only one of the windings 706.

[0039] Similarly, in embodiments where the windings 706d, 706e, 706f of the section 704 are connected to the terminals 406d, 406e, 406f using a "Y" configuration (e.g., the diagram shown in FIG. 8A), two of the windings 706 will be identified between each individual pair of terminals 406d, 406e, 406f. In embodiments where the windings 706d, 706e, 706f of the section 704 are connected to the terminals 406d, 406e, 406f using a "Δ" configuration (e.g., the diagram shown in FIG. 8B), each individual pair of terminals 406d, 406e, 406f will identify one winding 706 connected in parallel in combination with two other windings 706 connected in series. In an embodiment in which the windings 706d, 706e, 706f of section 704 are connected to three separate pairs of terminals (e.g., as illustrated in FIG. 8C ), each individual pair of terminals 406d, 406e, 406f will identify only one of the windings 706.

[0040] In any of the foregoing terminal configurations, the flux linkage with the rotor magnets, as seen between a given set of terminals, will depend on the area swept out by the turns of the winding 706 as seen by those terminals, and the amount of magnetic flux from the rotor captured by those areas. Thus, for any such terminal configuration, the flux linkage allowed by the winding 706 of a segment 702, as seen between a given pair of terminals 406 of the segment 702, will be substantially different from the flux linkage allowed by the winding 706 of a segment 704, as seen between a given pair of terminals 406 of the segment 704. The different electrical characteristics of the windings 706 of the two stator segments 702, 704 may allow the individual stator segments 702, 704 to be configured for optimal performance under significantly different operating regimes, e.g., torque and speed. In this manner, the stator sections 702, 704 may be relied upon for energy conversion in the complementary operating conditions for which they are designed, using the same magnetic structures and assemblies.

[0041] As illustrated in FIG. 7, the partition 702 may include multiple terminals (e.g., terminals 406a, 406b, and 406c) that may be connected to the controller 118a, and the partition 704 may similarly include multiple terminals (e.g., terminals 406d, 406e, and 406f) that may be connected to the controller 118b. The controllers 118a, 118b may each include a set of switches, e.g., metal oxide semiconductor field effect transistor (MOSFET) switches, and control circuitry configured to selectively open and control the switches to achieve the functionality described herein, for example. As illustrated in FIG. 7, in some implementations, the controller 118a may further be connected to a power source (or energy storage unit) 708a, and the controller 118b may further be connected to a power source (or energy storage unit) 708b. In some implementations, the power source (or energy storage unit) 708a may be separate from the power source (or energy storage unit) 708b. In other implementations, power source (or energy storage unit) 708a may be the same component as power source (or energy storage unit) 708b.

[0042] In implementations where controller 118a is connected to a power source, controller 118a may selectively apply multiple phases of a power signal to windings 706a, 706b, and 706c of section 702. Similarly, in implementations where controller 118b is connected to a power source, controller 118b may selectively apply multiple phases of a power signal to windings 706d, 706e, and 706f of section 704. In implementations where controller 118a is connected to an energy storage unit, controller 118a may instead regulate the supply of power from windings 706a, 706b, and 706c to energy storage unit 708a. Similarly, in implementations where controller 118b is connected to an energy storage unit, controller 118b may instead regulate the supply of power from windings 706d, 706e, and 706f to energy storage unit 708b. In some such implementations, one or more stator sections (e.g., section 702) may be configured as a motor having windings 706 with a first set of electrical properties, and the other section (e.g., section 704) may be configured as a generator having windings 706 with a second, different set of electrical properties. In other implementations, one or more stator sections (e.g., section 702) may be configured as a motor having windings 706 with a first set of electrical properties, and the other section (e.g., section 704) may also be configured as a motor, but with windings 706 with a second, different set of electrical properties. In yet other implementations, one or more stator sections (e.g., section 702) may be configured as a generator having windings 706 with a first set of electrical properties, and the other section (e.g., section 704) may also be configured as a generator, but with windings 706 with a second, different set of electrical properties.

[0043] As mentioned above, in some embodiments, a given stator structure (e.g., one of stator sections 702, 704) may include windings 706 for multiple electrical phases, and energy may be transferred between those windings 706 and an external network via terminals 406 located on that stator structure. For example, in the example machine 700 shown in FIG. 7, the stator section 702 includes three terminals 406a, 406b, and 406c that are electrically connected to three windings 706a, 706b, and 706c for individual phases supported by the stator section 702, and the stator section 704 includes three terminals 406d, 406e, and 406f that are electrically connected to three windings 706d, 706e, and 706f for individual phases supported by the stator section 704.

[0044] 8A-C illustrate three possible schemes for driving (or receiving power from) three windings (i.e., windings W1, W2, and W3) via multiple terminals. The schemes shown in FIGS. 8A and 8B allow the use of only three terminals (i.e., terminals T1, T2, and T3) to drive (or receive power from) the three windings (i.e., windings W1, W2, and W3) for the individual phases. On the other hand, the scheme shown in FIG. 8C requires additional terminals (e.g., terminals T1, T2, T3, T4, T5, and T6) to drive (or receive power from) the three windings (i.e., windings W1, W2, and W3) for the individual phases. The connection configuration shown in FIG. 8A is generally referred to as a "Y" configuration. The connection configuration shown in FIG. 8B is generally referred to as a "Δ" configuration. Any of the aforementioned configurations may be used to interconnect the windings 706 and terminals 406 of the individual stator sections 702, 704 shown in FIG. 7, and if the configuration of FIG. 8C is employed for any such sections, additional terminals may be provided.

[0045] With regard to implementations of machine 700 (shown in FIG. 7 ) in which a given stator section 702, 704 includes only three terminals for driving (or receiving power from) three windings, at least the following four configurations are possible: (1) the windings W1, W2, and W3 in FIG. 8A may correspond to the windings 706a, 706b, and 706c for the three phases of the stator section 702 shown in FIG. 7, and the terminals T1, T2, and T3 in FIG. 8A may correspond to the three terminals 406a, 406b, and 406c of the stator section 702 shown in FIG. 7; (2) the windings W1, W2, and W3 in FIG. 8A may correspond to the windings 706d, 706e, and 706f for the three phases of the stator section 704 shown in FIG. 7, and the terminals T1, T2, and T3 in FIG. 8A may correspond to the three terminals 406d, 406e, and 406f of the stator section 704 shown in FIG. 7; ( 7, and terminals T1, T2, and T3 in FIG. 8B may correspond to the three terminals 406a, 406b, and 406c of the stator section 702 shown in FIG. 7; or (4) windings W1, W2, and W3 in FIG. 8B may correspond to windings 706d, 706e, and 706f for the three phases of the stator section 704 shown in FIG. 7, and terminals T1, T2, and T3 in FIG. 8B may correspond to the three terminals 406d, 406e, and 406f of the stator section 704 shown in FIG. 7.

[0046] It can be understood that in any of the foregoing configurations, due to different winding configurations (e.g., different numbers of turns per winding) of stator sections 702, 704, the values ​​of various electrical properties (e.g., resistance, flux linkage, etc.) as measured between any two of terminals 406a, 406b, and 406c of stator section 702 when those terminals are not connected to an external circuitry will be substantially different from the values ​​of those same electrical properties as also measured between any two of terminals 406d, 406e, and 406f of stator section 704 when those terminals are not connected to an external circuitry. As used herein, a difference is considered to be "substantial" if it is greater than would be expected due to standard manufacturing tolerances.

[0047] 9 illustrates a second exemplary implementation of a planar axial flux machine 900 including a number of different stator construction types, as described in connection with FIGS. 4-6. Although only two stator sections 902, 904 are shown in FIG. 9, it should be understood that, as previously mentioned, one or more additional stator sections of either or both of the types illustrated, and / or one or more additional sections of a different type, may be employed in other implementations. As with FIG. 7, the upper rotor assembly 108a is not depicted in FIG. 9 to allow for a clearer view of the two exemplary stator sections 902, 904 included within the machine 900.

[0048] As shown, the stator section 902 of the machine 900 may be configured similarly to the stator section 702 (or stator section 704) shown in Figure 7 in that it may have one or more windings 706 connected to the controller 118 via one or more terminals 406, and in that the controller 118 may in turn be connected to a power source (or energy storage unit) 708, thus enabling the section 902 to operate in either a motor or generator mode. However, the section 904 of the machine 900 may be a conductive sheet of material (e.g., aluminum or copper) positioned within a gap in the active area of ​​the machine 900, and thus as the rotor rotates, eddy currents may be generated, thus causing the creation of a drag force on the rotor that increases as a function of rotor speed. As used herein, the term "conductive sheet" is meant to refer to any conductive structure that occupies a planar area such that eddy currents can be induced within the structure, and is thus intended to encompass conductive planar structures with holes or other discontinuities (e.g., planar mesh structures), as well as conductive planar structures without such discontinuities, such as a continuous aluminum or copper sheet.

[0049] Advantageously, the drag introduced through the sections 904 may be either selectively supplemented or selectively counteracted by appropriately operating the controller 118, thus allowing the motor or generator behavior of the sections 902 to fine-tune the level of drag imposed on the rotor of the machine 900. The combination of the stator sections 902 with the stator sections 904 in such a configuration may thus operate as an eddy current snubber, with programmable dynamics, through the action of the motor or generator of the stator 902. In some implementations, the overall drag coefficient of such a snubber may additionally or alternatively be varied by adjusting the degree to which the stator sections 904 protrude into the gap of the machine 900. The machine 900 may find useful applications in scenarios where an adjustable level of drag is desirable, such as for stationary cycling machines or other exercise equipment.

[0050] 10 is a partial cutaway view showing a third example implementation of a planar axial flux machine 1000 including a number of different stator construction types. Again, the upper rotor assembly 108a is not depicted in FIG. 10 to allow for a clearer view of the different stator construction types included within the machine 1000. As shown in FIG. 10, the machine 1000 may include a partition 1002 (and associated circuitry 118, 708) that is the same as or similar to the partition 902 (and associated circuitry 118, 708) described in connection with FIG. 9. The machine 1000 is thus similar to the machine 900 in terms of the ability of the controller 118 to operate the partition 1002 in a motor mode or a generator mode. However, machine 1000 differs from machine 900 (shown in FIG. 9 ) in that machine 1000 includes an annular sheet 1004 of conductive material (e.g., aluminum or copper) that extends throughout the entire active area of ​​machine 1000, including the area directly beneath section 1002, e.g., on a different layer than windings 706 of section 1002. As with section 904 of machine 900, as the rotor of machine 1000 rotates, eddy currents may be generated in annular sheet 1004 of machine 1000, thus causing the generation of a drag force on the rotor that increases as a function of rotor speed. As with machine 900, the drag force introduced via annular conductive sheet 1004 may be either selectively supplemented or selectively counteracted by appropriately operating controller 118, thus allowing the behavior of the motor or generator of section 1002 to fine-tune the level of drag force imposed on the rotor of machine 1000.

[0051] Although only one section 1002 is shown in FIG. 10, it should be understood that one or more additional stator sections 1002 and / or one or more additional sections of a different type (such as those described herein) may be employed in other implementations.

[0052] FIG. 11 illustrates an example of a planar axial flux machine 1100 having a novel section configuration that can be employed either alone or with one or more additional or different section structures. As shown, the machine 1100 may include a section 1102 including one or more windings 1104 connected to a controller 1106 via two or more terminals 1108. The controller 1106 may include one or more switches, e.g., MOSFET switches, and control circuitry configured to selectively open and control such switches, for example, to achieve the functionality described herein. As also shown, in some implementations, the controller 1106 may further be connected to one or more dissipative elements 1110 (e.g., one or more resistors). In some implementations, a switch of the controller 1106b may be selectively closed to connect a dissipative element between a pair of terminals 1108 that are connected to respective ends of the winding 1104. By interconnecting the ends of the windings 1104 in such a manner, the motion of the rotor may cause eddy currents to circulate through the windings 1104 and the dissipative element 1110, thus generating a drag force on the rotor of the machine 1100 that varies as a function of rotor speed, similar to the behavior of the conductive sheets 904, 1004 described above. Varying the value of the dissipative element 1110 may allow the magnitude of such drag to be adjusted. Thus, in some implementations, the switches of the controller 1106 may be rapidly opened and closed at different rates to adjust the average value of resistance seen between the terminals 1108. In some implementations, the dissipative element 1110 may be omitted, and the switches of the controller 1106 may instead directly interconnect the terminals 1108 to achieve a similar result, but without the additional power dissipation provided by a resistor or equivalent.

[0053] In some implementations, multiple windings 1104 may be employed on one or more such sections 1102, and the controller 1106 may selectively establish connections (either directly or via one or more dissipative elements 1110) between pairs of terminals that are electrically connected to ends of the individual windings 1104. In such embodiments, the amount of drag imposed on the rotor of the machine 1100 may additionally or alternatively be adjusted by modifying some of the individual windings 1104 to which such connections are established. Although only one section 1102 is shown in FIG. 11, it should be understood that one or more additional stator sections 1102 and / or one or more additional sections of a different type (such as those described herein) may be employed in other implementations.

[0054] FIG. 12 illustrates a fourth exemplary implementation of a planar axial flux machine 1200 including a number of different stator construction types as described in connection with FIGS. 4-6. As with the other embodiments, the upper rotor assembly 108a is not depicted in FIG. 12 to allow for a clearer view of the two exemplary stator sections 1202, 1204 included within the machine 1200. As shown, the machine 1200 may include both (A) a section 1202 and associated circuitry 1106, 1110, similar to the section 1102 and associated circuitry 1106, 1110 of the machine 1100 (shown in FIG. 11 ), and (B) a stator section 1204 and associated circuitry 118, 708, similar to the stator section 702 (or stator section 704) shown in FIG. 7. In some implementations, the stator section 1204 and associated circuitry 118, 708 may operate as a motor or generator, and the stator section 1202 may operate as a controllable brake (or other drag-generating component) for the rotor of the machine 1200. Although only two stator sections 1202, 1204 are shown in FIG. 12, it should be understood that, as mentioned above, one or more additional stator sections of either or both of the types shown, and / or one or more additional sections of a different type may be employed in other implementations.

[0055] 12, section 1202 and section 1204 may each include one or more windings 706, 1104. In some implementations, the winding 1104 of section 1202 may be electrically isolated from and have substantially different electrical characteristics than the winding 706 of section 1204. In the illustrated embodiment, for example, section 1204 includes windings 706a, 706b, and 706c for three separate phases, such windings per phase forming a total of four turns, while section 1202 includes only one winding 1104, forming a total of eight turns.

[0056] In an embodiment where the windings 706a, 706b, 706c of the section 1204 are connected to the terminals 406a, 406b, 406c using a "Y" configuration (e.g., the diagram shown in FIG. 8A), two of the windings 706 will be identified between each individual pair of terminals 406a, 406b, 406c. In an embodiment where the windings 706a, 706b, 706c of the section 1204 are connected to the terminals 406a, 406b, 406c using a "Δ" configuration (e.g., the diagram shown in FIG. 8B), each individual pair of terminals 406a, 406b, 406c will identify one winding 706 connected in parallel in combination with two other windings 706 connected in series. In an embodiment in which the windings 706a, 706b, 706c of the section 1204 are connected to three separate pairs of terminals (e.g., the diagram depicted in FIG. 8C ), each individual pair of terminals 406a, 406b, 406c will identify only one of the windings 706.

[0057] In any of the foregoing terminal configurations, the flux linkage with the rotor magnets, as seen between a given set of terminals, will depend on the area swept out by the turns of the winding 706 seen by those terminals, and the amount of magnetic flux from the rotor captured by those areas. Thus, for any such terminal configuration, the flux linkage allowed by the winding 1104 of the section 1202, as seen between the terminals 1206a, 1206b, will be substantially different from the flux linkage allowed by the winding 706 of the section 1204, as seen between the respective pairs of terminals 406. The different electrical characteristics of the windings 1104, 706 of the two stator sections 1202, 1204 may thus enable the individual stator sections to be configured to perform their respective functions (e.g., motor / generator action and braking action) in an optimal manner.

[0058] In a similar manner to the embodiment disclosed in connection with FIG. 7 , it can be understood that due to the different winding configurations of the stator sections 1202, 1204 (e.g., different numbers of turns per winding), the values ​​of various electrical properties (e.g., resistance, magnetic flux linkage, etc.) between the two terminals 1206a, 1206b of the stator section 702 as measured when those terminals are not connected to an external circuitry will be substantially different from the values ​​of those same electrical properties between any two of the terminals 406a, 406b, and 406c of the stator section 1204 as also measured when those terminals are not connected to an external circuitry.

[0059] FIG. 13 illustrates a fifth exemplary implementation of a planar axial flux machine 1300 including multiple different stator structure types as described in connection with FIGS. 4-6. Again, the upper rotor assembly 108a is not depicted in FIG. 13 to allow for a clearer view of the two exemplary stator structures 1302, 1304 included within the machine 1300. As shown, the machine 1300 may include both (A) a stator section 1302 and associated circuitry 1106, 1110, similar to the stator section 1102 and associated circuitry 1106, 1110 of the machine 1100 (shown in FIG. 11 ), and (B) a stator section 1304 including a conductive sheet of material (e.g., aluminum or copper) positioned within a gap within the active area of ​​the machine 1300 such that as the rotor rotates, eddy currents may be generated, thus causing the generation of drag forces on the rotor that increase as a function of rotor speed. In some implementations, the stator section 1302 and associated circuitry 1106, 1110 may operate to selectively supplement the drag imposed on the rotor of the machine 1300 via the stator section 1304, thus allowing fine tuning of the level of drag imposed on the rotor of the machine 1300. Although only two stator sections 1302, 1304 are shown in FIG. 13, as mentioned above, it should be understood that one or more additional stator sections of either or both of the types shown, and / or one or more additional sections of a different type may be employed in other implementations.

[0060] 14 is a partial cutaway view showing a sixth exemplary implementation of a planar axial flux machine 1400 including a number of different stator structure types. Again, the upper rotor assembly 108a is not depicted in FIG. 14 to allow for a clearer view of the two exemplary stator structures 1402, 1404 included in the machine 1300. As shown, the machine 1400 may include both (A) a stator section 1402 and associated circuitry 1106, 1110, similar to the stator section 1102 and associated circuitry 1106, 1110 of the machine 1100 (shown in FIG. 11 ), and (B) an annular sheet 1404 of conductive material (e.g., aluminum or copper) positioned in a gap within the active area of ​​the machine 1400 such that as the rotor rotates, eddy currents may be generated, thus generating a drag force on the rotor that increases as a function of rotor speed.

[0061] Similar to machine 1300 (shown in FIG. 13), in some implementations stator sections 1402 and associated circuitry 1106, 1110 may operate to selectively complement the drag imposed on the rotor of machine 1300 via annular conductive sheet 1404, thus allowing fine tuning of the level of drag imposed on the rotor of machine 1400. While only two stator construction types are shown in FIG. 14, as mentioned above, it should be understood that one or more additional stator sections of either or both of the types shown, and / or one or more additional sections of a different type may be employed in other implementations.

[0062] The advantages of the various stator designs described herein are numerous. For some of the embodiments described above, similar performance could be obtained by mechanically combining a conventional motor with a conventional snubber. Such a motor and snubber solution would require thermal solutions, multiple shafts, and mechanical integration. The use of some of the stator machine configurations described herein would eliminate these considerations.

[0063] Similar performance could be obtained by connecting a controllable eddy current brake on the same shaft as the motor to the other exemplary embodiments described above. Again, such a solution would increase the complexity and cost of the system. In particular, additional magnetic structures would be required for the braking feature, such as electromagnets requiring an external power source, or additional magnets used only when braking. Use of some of the stator machine configurations described herein would again eliminate these considerations.

[0064] To yet other exemplary embodiments described above, similar performance may be obtained by connecting two or more motors designed for different motion regimes on the same shaft. Various mechanical challenges would be associated with such a design. Use of some of the stator machine configurations described herein would allow the motor sections to share the same magnetic circuit, rotor material, and bearings. This would result in a simpler and more cost-effective design.

[0065] Embodiments of the type of machine described herein address a number of application areas, examples of which include, but are not limited to, the following:

[0066] One application is in therapeutic or exercise equipment, where the role of the machine is to resist forces applied by a human and absorb or convert some of the applied forces into power while simulating a target activity. Such activities may include the force and inertia characteristics of lifting a barbell, the drag of rowing a boat, the variable resistance associated with cycling, and the like. The dynamics required to simulate these activities may be achieved, for example, through feedback control of conventional servo motors combined with energy storage and dissipation mechanisms. The use of some of the stator machine configurations described herein would allow motor action to be integrated with dissipative stator elements, with benefits including reduced overall system cost and complexity.

[0067] In some implementations, multiple motor stator designs may additionally or alternatively be combined within the gap to meet a wide range of requirements within the same machine. For example, a motor stator section designed for low torque, high speed operation may be combined with a motor stator section for high torque, low speed operation.

[0068] In some implementations, one or more motor / generator sections may additionally or alternatively be combined with a section specialized for inductive braking under active control. In this case, for example, a direct drive wind turbine generator (one section) may have a braking mechanism (braking section) that regulates turbine speed under high wind conditions. In similar motor applications, the braking section may provide an emergency shaft stop function.

[0069] The following paragraphs (P1)-(P8) describe examples of the inventive concepts disclosed herein.

[0070] (P1) A planar stator for an axial flux machine (having a rotor including one or more magnets generating a first magnetic flux generally parallel to an axis of rotation of the rotor within an active area in a gap of the axial flux machine) has at least first, second, third, and fourth terminals, each adapted to be connected to a circuit network external to the planar stator, and at least one first winding arranged to be positioned within the active area, the at least one first winding having first and second ends electrically connected to the first and second terminals, respectively, and the first and second terminals being arranged to be connected to a winding. The at least one second winding may include at least one first winding, wherein an electrical characteristic between the first terminal and the second terminal as measured when not connected to a circuit network has a first value, and at least one second winding arranged to be positioned within the active area, the at least one second winding being electrically isolated from the at least one first winding and having third and fourth ends electrically connected to the third and fourth terminals, respectively, wherein the electrical characteristic between the third terminal and the fourth terminal as measured when the third and fourth terminals are not connected to a circuit network has a second value that is substantially different from the first value.

[0071] (P2) The planar stator may be configured as described in paragraph (P1), and the at least one first winding may be disposed on a first stator section and the at least one second winding may be disposed on a second stator section that is angularly offset from the first stator section relative to the axis of rotation.

[0072] (P3) The planar stator may be configured as described in paragraph (P1) or paragraph (P2), and the at least one first winding may include the first winding and at least one additional winding, and the circuitry may include a power source, and the first winding may be configured to support a first phase from the power source, and the at least one additional winding may be configured to support the at least one additional phase from the power source such that a peak value of a second magnetic flux generated by a combination of the first winding and the at least one additional winding follows an arcuate path relative to the axis of rotation.

[0073] (P4) The planar stator may be configured as described in any of paragraphs (P1)-(P3), and the electrical characteristic may include resistance, and a first resistance between the first terminal and the second terminal as measured when the first and second terminals are not connected to a circuit network may be at least 50% greater than a second resistance between the third terminal and the fourth terminal as measured when the third and fourth terminals are not connected to a circuit network.

[0074] (P5) The planar stator may be configured as described in any of paragraphs (P1)-(P4), and the electrical characteristics may include a flux linkage with a first magnetic flux, and the first flux linkage between the at least one first winding and the first magnetic flux as identified between the first terminal and the second terminal may be at least 50% greater than a second flux linkage between the at least one second winding and the first magnetic flux as identified between the third terminal and the fourth terminal.

[0075] (P6) The planar stator may be configured as described in any of paragraphs (P1)-(P5), and the circuitry includes a first controller configured to selectively couple the first and second terminals to a power source, such that during at least a first operating mode of the axial flux machine, the at least one first winding may generate a second magnetic flux generally parallel to the axis of rotation.

[0076] (P7) The planar stator may be configured as described in any of paragraphs (P1)-(P6), and the circuitry further includes a second controller configured to selectively couple the third and fourth terminals to the power source, such that during at least a second operating mode of the axial flux machine, the at least one second winding may generate a third magnetic flux generally parallel to the axis of rotation.

[0077] (P8) The planar stator may be configured as described in any of paragraphs (P1)-(P7) and may further include at least one switch configured to be selectively closed to establish an electrical connection between the third terminal and the fourth terminal during a time when the at least one second winding is not coupled to the external power source.

[0078] (P9) The planar stator may be configured as described in paragraph (P8), and the at least one switch may be configured to establish an electrical connection between the third terminal and the fourth terminal via the at least one dissipative element.

[0079] (P10) The planar stator may be configured as described in paragraph (P8) or paragraph (P9), and the circuitry may further include a second controller configured to modulate at least one switch to control a time-averaged conductivity between the third terminal and the fourth terminal.

[0080] (P11) The planar stator may be configured as described in any of paragraphs (P1)-(P10), and the circuitry further comprises a second controller configured to selectively couple the third and fourth terminals to the energy storage element, such that during at least a second operating mode of the axial flux machine, the energy storage element may receive power generated by the second winding in response to rotation of the rotor.

[0081] (P12) The planar stator may be configured as described in any of paragraphs (P1)-(P11), and the circuitry further comprises a first controller configured to selectively couple the first and second terminals to the energy storage element, such that during at least a first operating mode of the axial flux machine, the energy storage element may receive power generated by the first winding in response to rotation of the rotor.

[0082] (P13) The planar stator may be configured as described in any of paragraphs (P1)-(P12), and the circuitry further comprises a second controller configured to selectively couple the third and fourth terminals to the energy storage element, such that during at least a second operating mode of the axial flux machine, the energy storage element may receive power generated by the second winding in response to rotation of the rotor.

[0083] (P14) The planar stator may be configured as described in any of paragraphs (P1)-(P13) and may further include at least one switch configured to be selectively closed to establish an electrical connection between the first terminal and the second terminal during a time when the at least one first winding is not coupled to an external power source.

[0084] (P15) The planar stator may be configured as described in paragraph (P14), and the at least one switch may be configured to establish an electrical connection between the first terminal and the second terminal via the at least one dissipative element.

[0085] (P16) The planar stator may be configured as described in paragraph (P14) or paragraph (P15), and the circuitry may further comprise a second controller configured to modulate at least one switch to control a time-averaged conductivity between the first terminal and the second terminal.

[0086] (P17) A planar stator for an axial flux machine (having a rotor including one or more magnets generating a first magnetic flux generally parallel to the axis of rotation of the rotor within an active area in a gap of the axial flux machine) may include a first conductive sheet arranged to be positioned within the active area such that generation of eddy currents in the first conductive sheet imposes a drag force on the rotor, and at least a first winding arranged to be positioned within the active area, the first winding having at least first and second terminals electrically connected to respective ends of the first winding.

[0087] (P18) The planar stator may be configured as described in paragraph (P17) and further includes a controller configured to selectively couple the first and second terminals to a power source such that during at least a first operating mode of the axial flux machine, the first winding generates a second magnetic flux generally parallel to the axis of rotation.

[0088] (P19) The planar stator may be configured as described in paragraph (P17) or paragraph (P18) and further includes a controller configured to selectively couple the first and second terminals to the energy storage element such that during at least a first operating mode of the axial flux machine, the energy storage element receives power generated by the first winding in response to rotation of the rotor.

[0089] (P20) The planar stator may be configured as described in any of paragraphs (P17)-(P19) and may further include at least one switch configured to be selectively closed to establish an electrical connection between the first terminal and the second terminal at a time when the first winding is not coupled to an external power source.

[0090] (P21) The planar stator may be configured as described in paragraph (P20), and the at least one switch may be configured to selectively establish an electrical connection between the first terminal and the second terminal via the at least one dissipative element.

[0091] (P22) The planar stator may be configured as described in paragraph (P20) or paragraph (P21) and may further comprise a controller configured to modulate at least one switch to control a time-averaged conductivity between the first terminal and the second terminal.

[0092] (P23) A planar stator for an axial flux machine (having a rotor including one or more magnets generating a first magnetic flux generally parallel to an axis of rotation of the rotor within an active area in a gap of the axial flux machine) may include at least a first winding arranged to be positioned within the active area, the first winding having at least first and second terminals electrically connected to respective ends of the first winding, and at least one switch configured to be selectively closed to establish an electrical connection between the first terminal and the second terminal at times when the first winding is not coupled to an external power source.

[0093] (P24) The planar stator may be configured as described in paragraph (P23), and the at least one switch may be further configured to establish an electrical connection between the first terminal and the second terminal via the at least one dissipative element.

[0094] (P25) The planar stator may be configured as described in paragraph (P23) or paragraph (P24) and may further include a controller configured to modulate the at least one switch to control a time-averaged conductivity between the first terminal and the second terminal.

[0095] (P26) An axial flux machine, wherein at least two planar stator sections are arranged around an axis of rotation, the planar sections being different, and at least one stator section being a printed circuit stator capable of producing motor action under suitable control.

[0096] (P27) A machine as described in paragraph (P26), wherein at least one stator section is a printed circuit stator capable of producing motor action and at least one stator section is a plate of conductive material.

[0097] (P28) A machine as described in paragraph (P27) in which a plate of conductive material can be moved radially into or out of the gap.

[0098] (P29) A machine described in any one of paragraphs (P26)-(P28), wherein at least one stator section is a printed circuit stator capable of producing motor action and at least one stator section is a printed circuit eddy current brake operable under external control.

[0099] (P30) A machine as described in any one of paragraphs (P26)-(P29), in which the planar stator sections are interchangeable.

[0100] (P31) A machine described in any of paragraphs (P26)-(P30), wherein at least one stator section and at least one conductive plate are arranged around the rotating shaft.

[0101] (P32) A machine described in any one of paragraphs (P26)-(P31), wherein the conductive plate is constructed and arranged to be radially adjustable into or out of the gap.

[0102] (P33) A machine as described in any one of paragraphs (P26)-(P32), wherein the conductive plates and the stator sections are configured to be replaceable.

[0103] While several aspects of at least one embodiment have been described above, it should be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of this disclosure. Accordingly, the foregoing description and drawings are by way of example only.

[0104] Various aspects of the disclosure may be used alone, in combination, or in various arrangements not specifically discussed in the embodiments described above, and therefore this application is not limited to the details and arrangements of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

[0105] Also, the disclosed aspects may be embodied as a method, certain examples of which are provided. The acts performed as part of the method may be ordered in any suitable manner. Thus, embodiments may be constructed in which acts are performed in an order different from that shown, which may include performing some acts simultaneously even though in the illustrative embodiments are shown as sequential acts.

[0106] The use of ordinal terms such as "first," "second," "third," etc. in the claims to modify claim elements does not, by itself, imply any priority, precedence, or ordering of one claim element over another, or the temporal order in which acts of a method are performed, but is merely used as a label to distinguish one claimed element having a certain name from another element having the same name (in the absence of the use of ordinal terms) to distinguish claim elements.

[0107] Also, the phraseology and terminology used herein is used for purposes of description and should not be regarded as limiting. The use of "including," "comprising," "having," "containing," "with," and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof and additional items.

[0108] The charges are as follows:

Claims

1. A planar stator configured to be disposed in an axial gap between a first portion of a rotor of an axial flux machine and a second portion of the rotor, the rotor including one or more magnets, the one or more magnets generating a first magnetic flux generally parallel to an axis of rotation of the rotor within an active area in the axial gap, the planar stator comprising: a first discrete stator section including a first printed circuit board (PCB) substrate; at least first and second terminals supported by the first PCB substrate, the first and second terminals adapted to be connected to a first circuitry external to the planar stator; at least a first winding supported by the first PCB substrate, the first winding arranged to be positioned within the active area, the first winding having first and second ends electrically connected to the first and second terminals, respectively, and an electrical characteristic between the first terminal and the second terminal as measured when the first and second terminals are not connected to any circuitry external to the first discrete stator section has a first value; a second discrete stator section different from the first discrete stator section, the second discrete stator section including a second PCB substrate; at least third and fourth terminals carried by the second PCB substrate, the third and fourth terminals adapted to be connected to a second circuitry external to the planar stator; at least a second winding supported by the second PCB substrate, the second winding arranged to be positioned within the active area, the second winding being electrically isolated from the first winding and having third and fourth ends electrically connected to the third and fourth terminals, respectively, and an electrical characteristic between the third and fourth terminals as measured when the third and fourth terminals are not connected to any circuitry external to the second discrete stator section has a second value substantially different from the first value; A planar stator comprising:

2. A planar stator as described in claim 1, wherein the second stator section is offset at an angle from the first stator section relative to the axis of rotation and does not overlap with the first stator section.

3. an additional winding supported by the first PCB substrate; the first network includes a power source; the first winding is configured to support a first phase from the power source; 3. The planar stator of claim 2, in combination with the first network, wherein the additional winding is configured to support a second phase from the power source such that a peak value of a second magnetic flux generated by a combination of the first winding and the additional winding follows an arcuate path relative to the axis of rotation.

4. 2. The planar stator of claim 1, wherein the electrical characteristic is resistance, and a first resistance between the first and second terminals as measured when the first and second terminals are not connected to any circuitry external to the first stator section is at least 50% greater than a second resistance between the third and fourth terminals as measured when the third and fourth terminals are not connected to any circuitry external to the second stator section.

5. The planar stator of claim 1 , wherein the electrical property is flux linkage with the first magnetic flux.

6. A planar stator as described in claim 5, wherein a first magnetic flux linkage between the at least one first winding and the first magnetic flux as identified between the first terminal and the second terminal is at least 50% greater than a second magnetic flux linkage between the at least one second winding and the first magnetic flux as identified between the third terminal and the fourth terminal.

7. The first winding includes a first number of turns, The planar stator of claim 5 , wherein the second winding includes a second number of turns different than the first number of turns.

8. 10. The planar stator of claim 1 in combination with said first circuitry, said first controller configured to selectively couple said first and second terminals to a power source such that said first winding generates a second magnetic flux generally parallel to said axis of rotation during at least a first mode of operation of said axial flux machine.

9. 10. The combination of claim 8 in further combination with said second circuitry, said second circuitry further including a second controller configured to selectively couple said third and fourth terminals to a power source such that said second winding generates a third magnetic flux generally parallel to the axis of rotation during at least a second mode of operation of the axial flux machine.

10. The combination of claim 8, further comprising at least one switch configured to be selectively closed to establish an electrical connection between the third terminal and the fourth terminal during times when the second winding is not coupled to an external power source.

11. The combination of claim 10 , wherein the at least one switch is configured to establish the electrical connection between the third terminal and the fourth terminal through at least one dissipative element.

12. 12. The combination of claim 11 , wherein the second circuitry further comprises a second controller configured to modulate the at least one switch to control a time-averaged conductivity between the third terminal and the fourth terminal.

13. 9. The combination of claim 8, wherein the second circuitry further comprises a second controller configured to selectively couple the third and fourth terminals to the energy storage element such that during at least a second operating mode of the axial flux machine, the energy storage element receives power generated by the second winding in response to rotation of the rotor.

14. 10. The planar stator of claim 1 in combination with said first circuitry, said first controller configured to selectively couple said first and second terminals to said energy storage element such that during at least a first operating mode of the axial flux machine, the energy storage element receives power generated by the first winding in response to rotation of the rotor.

15. 15. The combination of claim 14 in further combination with said second circuitry, said second circuitry further comprising a second controller configured to selectively couple said third and fourth terminals to said energy storage element such that during at least a second operating mode of the axial flux machine, the energy storage element receives power generated by the second winding in response to rotation of the rotor.

16. The combination of claim 14, further comprising at least one switch configured to be selectively closed to establish an electrical connection between the third terminal and the fourth terminal during times when the second winding is not coupled to an external power source.

17. 17. The combination of claim 16, wherein the at least one switch is configured to establish the electrical connection between the third terminal and the fourth terminal through at least one dissipative element.

18. 20. The combination of claim 17 in further combination with the second circuitry, the second circuitry further comprising a second controller configured to modulate the at least one switch to control a time-averaged conductivity between the third terminal and the fourth terminal.

19. A planar stator as described in claim 1 in combination with the rotor.

20. The one or more magnets include at least one first magnet included on the first portion of the rotor and at least one second magnet included on the second portion of the rotor; 20. The combination of claim 19, wherein the axial gap is located between the at least one first magnet and the at least one second magnet.

21. The combination of claim 19 in further combination with the first circuitry and the second circuitry.

22. The combination described in claim 21, wherein the first circuitry includes a first controller configured to selectively couple the first and second terminals to a power source such that the first winding generates a second magnetic flux substantially parallel to the rotational axis during at least a first operating mode of the axial flux machine.

23. The combination described in claim 22, wherein the second circuitry further includes a second controller configured to selectively couple the third and fourth terminals to a power source so that the second winding generates a third magnetic flux substantially parallel to the rotational axis during at least a second operating mode of the axial flux machine.

24. The combination of claim 22, further comprising at least one switch configured to be selectively closed to establish an electrical connection between the third terminal and the fourth terminal during times when the second winding is not coupled to an external power source.

25. The combination described in claim 22, wherein the second circuitry further comprises a second controller configured to selectively couple the third and fourth terminals to the energy storage element such that during at least a second operating mode of the axial flux machine the energy storage element receives power generated by the second winding in response to rotation of the rotor.

26. The combination described in claim 21, wherein the first circuitry further comprises a first controller configured to selectively couple the first and second terminals to the energy storage element such that during at least a first operating mode of the axial flux machine, the energy storage element receives power generated by the first winding in response to rotation of the rotor.

27. ​​The combination described in claim 26, wherein the second circuitry further comprises a second controller configured to selectively couple the third and fourth terminals to the energy storage element such that during at least a second operating mode of the axial flux machine the energy storage element receives power generated by the second winding in response to rotation of the rotor.

28. The first winding includes a first number of turns, The planar stator of claim 1 , wherein the second winding includes a second number of turns different than the first number of turns.

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