Planar stator configuration for axial magnetic flux machine

Abstract

To provide a planar stator configuration for an axial magnetic flux machine.SOLUTION: In some embodiments, two or more different types of a stator structure may be disposed within a gap of an axial magnetic flux machine. Such an arrangement may be advantageous, for example, to produce a machine that is optimized for multiple modes of operation, such as generation of mechanical torque, conversion of mechanical torque to electrical power and / or dissipation of mechanical power. Further, in some embodiments, the axial magnetic flux machine may include a planar stator having winding arranged to be positioned within an active region of the machine, and may further include at least one switch configured to be selectively closed in order to establish electrical connection between separate ends of the winding at time when the winding is not coupled to an external power source.SELECTED DRAWING: None

Description

Background Art

[0001] (Cross - reference to related applications) This application claims the benefit under 35 U.S.C.§119(e) (Section 119(e) of the United States Patent Law) of U.S. Provisional Application No. 63 / 150,129, filed on February 17, 2021, entitled "MULTI - STATOR AXIAL FLUX MACHINE".

[0002] Axial flux motors and generators, as described by several patents, including U.S. Patent No. 7,109,625 (Patent Document 1) ("the '625 patent"), the entire contents of which are incorporated herein by reference, feature a planar printed circuit board stator assembly interposed between rotor assemblies that support magnets with alternating N - S poles. The magnetic flux between the magnets interacts with the current density supported by the wiring in the printed circuit stator to produce torque.

[0003] This type of electrical machine can operate either as a motor or a generator and has several useful properties, including that the torque as a function of angle is smooth and can possess high - quality motion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0005] This summary is provided to introduce, in a simplified form, a series of concepts 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 included with this specification.

[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 substantially parallel to the axis of rotation of the rotor within the active region within the gap of the axial flux machine) includes at least first, second, third, and fourth terminals, each adapted to be connected to an external network of the planar stator, at least one first winding arranged to be positioned within the active region, the at least one first winding having first and second ends respectively electrically connected to the first and second terminals, the electrical characteristics between the first and second terminals as measured when the first and second terminals are not connected to the network having a first value, the at least one first winding, at least one second winding arranged to be positioned within the active region, the at least one second winding being electrically insulated from the at least one first winding and having third and fourth ends respectively electrically connected to the third and fourth terminals, the electrical characteristics between the third and fourth terminals as measured when the third and fourth terminals are not connected to the network having a second value 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 substantially parallel to the axis of rotation of the rotor within the active region within the gap of the axial flux machine) includes a first conductive sheet arranged to be positioned within the active region such that the generation of eddy currents within the first conductive sheet imposes a drag force on the rotor, and at least one first winding arranged to be positioned within the active region, the at least one first winding having at least first and second terminals electrically connected to respective individual ends of the first winding.

[0008] In some embodiments, a planar stator for an axial flux machine having a rotor that includes one or more magnets that generate a first magnetic flux substantially parallel to the axis of rotation of the rotor within an active region within the gap of the axial flux machine, the planar stator comprising at least a first winding arranged to be positioned within the active region, the first winding having at least first and second terminals that are electrically connected to respective ends of the first winding, and at least one switch configured to selectively close to establish an electrical connection between the first and second terminals at times when the first winding is not coupled to an external power source. The present invention provides, for example, the following. (Item 1) A planar stator for an axial flux machine having a rotor that includes one or more magnets, the one or more magnets generating a first magnetic flux substantially parallel to the axis of rotation of the rotor within an active region within the gap of the axial flux machine, the planar stator comprising: at least first, second, third, and fourth terminals, each adapted to be connected to an external network of the planar stator; at least one first winding arranged to be positioned within the active region, the at least one first winding having first and second ends electrically connected to the first and second terminals respectively, the electrical characteristics between the first and second terminals as measured when the first and second terminals are not connected to the network having a first value; at least one first winding; At least one second winding arranged to be positioned within the active region, wherein the at least one second winding is electrically insulated from the at least one first winding and has third and fourth ends respectively electrically connected to the third and fourth terminals, and the electrical characteristics between the third and fourth terminals as measured when the third and fourth terminals are not connected to the circuit network have a second value that is substantially different from the first value, at least one second winding A planar stator comprising. (Item 2) The at least one first winding is disposed on a first stator section, The at least one second winding is disposed on a second stator section that is offset at an angle from the first stator section with respect to the axis of rotation, The planar stator according to item 1. (Item 3) The at least one first winding includes a first winding and at least one additional winding, The circuit network includes a power source, The first winding is configured to support a first phase from the power source, The at least one additional winding is configured to support at least one additional phase from the power source such that the peak value of the second magnetic flux generated by the combination of the first winding and the at least one additional winding follows an arcuate path with respect to the axis of rotation, The planar stator according to item 2. (Item 4) The electrical characteristic is resistance, and the first resistance between the first and second terminals as measured when the first and second terminals are not connected to the circuit network is at least 50% greater than the second resistance between the third and fourth terminals as measured when the third and fourth terminals are not connected to the circuit network. The planar stator according to item 1. (Item 5) The electrical characteristic is a magnetic flux linkage with the first magnetic flux, and the first magnetic flux linkage between the at least one first winding and the first magnetic flux, as confirmed between the first terminal and the second terminal, is at least 50% greater than the second magnetic flux linkage between the at least one second winding and the first magnetic flux, as confirmed between the third terminal and the fourth terminal, for the planar stator according to item 1. (Item 6) The circuit network includes a first controller configured to selectively couple the first and second terminals to a power source, and thus, during at least a first operating mode of the axial flux machine, the at least one first winding generates a second magnetic flux substantially parallel to the axis of rotation, for the planar stator according to item 1. (Item 7) The circuit network further includes a second controller configured to selectively couple the third and fourth terminals to a power source, and thus, during at least a second operating mode of the axial flux machine, the at least one second winding generates a third magnetic flux substantially parallel to the axis of rotation, for the planar stator according to item 6. (Item 8) The planar stator according to item 6 further includes at least one switch configured to be selectively closed to establish an electrical connection between the third terminal and the fourth terminal when the at least one second winding is not coupled to an external power source. (Item 9) The at least one switch is configured to establish the electrical connection between the third terminal and the fourth terminal via at least one dissipative element, for the planar stator according to item 8. (Item 10) The circuit network according to item 9 further includes a second controller configured to modulate the at least one switch to control the time-averaged conductivity between the third terminal and the fourth terminal, for the planar stator. (Item 11) The circuit network further comprises a second controller configured to selectively couple the third and fourth terminals to an 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. The planar stator according to item 6. (Item 12) The circuit network comprises a first controller configured to selectively couple the first and second terminals to an 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. The planar stator according to item 1. (Item 13) The circuit network further comprises a second controller configured to selectively couple the third and fourth terminals to an 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. The planar stator according to item 12. (Item 14) The planar stator according to item 12 further comprises at least one switch configured to be selectively closed to establish an electrical connection between the third and fourth terminals during a time when the at least one second winding is not coupled to an external power source. (Item 15) The at least one switch of the planar stator according to item 14 is configured to establish the electrical connection between the third and fourth terminals via at least one dissipative element. (Item 16) The circuit network of the planar stator according to item 15 further comprises a second controller configured to modulate the at least one switch to control the time-averaged conductivity between the first and second terminals. (Item 17) A planar stator for an axial flux machine having a rotor including one or more magnets, wherein the one or more magnets generate a first magnetic flux substantially parallel to the axis of rotation of the rotor within an active region within the air gap of the axial flux machine, the planar stator comprising: A first conductive sheet, the first conductive sheet being arranged to be positioned within the active region such that the generation of eddy currents within the first conductive sheet imposes a drag force on the rotor; At least a first winding arranged to be positioned within the active region, the first winding having at least first and second terminals electrically connected to respective ends of the first winding; A planar stator comprising: (Item 18) The planar stator according to item 17, further comprising 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 substantially parallel to the axis of rotation. (Item 19) The planar stator according to item 17, further comprising a controller configured to selectively couple the first and second terminals to an 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. (Item 20) The planar stator according to item 17, further comprising at least one switch configured to selectively close to establish an electrical connection between the first and second terminals at times when the first winding is not coupled to an external power source. (Item 21) The planar stator according to item 20, wherein the at least one switch is configured to selectively establish the electrical connection between the first and second terminals via at least one dissipative element. (Item 22) The planar stator according to item 21, further comprising a controller configured to modulate the at least one switch to control the time-averaged conductivity between the first terminal and the second terminal. (Item 23) A planar stator for an axial-flux machine having a rotor including one or more magnets, wherein the one or more magnets generate a first magnetic flux substantially parallel to the axis of rotation of the rotor within an active region within the air gap of the axial-flux machine, and the planar stator At least a first winding arranged to be positioned within the active region, the first winding having at least first and second terminals electrically connected to respective ends of the first winding, at least a first winding; At least one switch, the at least one switch being configured to be selectively closed to establish an electrical connection between the first terminal and the second terminal when the first winding is not coupled to an external power source. At least one switch Comprising a planar stator. (Item 24) The planar stator according to item 23, wherein the at least one switch is further configured to establish the electrical connection between the first terminal and the second terminal via at least one dissipative element. (Item 25) The planar stator according to item 24, further comprising a controller configured to modulate the at least one switch to control the time-averaged conductivity between the first terminal and the second terminal.

Brief Description of the Drawings

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

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[0026] Detailed Description A variation of the machine described in the '625 patent uses a stator that does not draw a complete annulus. In particular, one or more planar stator segments, fabricated using printed circuit board (PCB) processing or similar techniques, can be placed within the gap between the rotors. Machines of this type are described in U.S. Patent Application Publication No. 2020 / 067361 (the “'361 Publication”), the entire contents of which are incorporated herein by reference, and can support angle-dependent torque requirements. In these types of applications, the portion of the rotor that is densely filled with magnets is aligned with the stator segment at the angle at which maximum torque is required thereof. Also, what is discussed in the '361 Publication is a possibility of a machine that is similar to the rotor in the '625 patent in that the stator therein includes one or more segments, while the rotor is uniformly filled with magnetic poles. A machine similar to that described in the '625 patent can be fabricated by assembling a complete annular ring from segments, as opposed to fabricating the machine from a monolithic circuit board.

[0027] Disclosed herein is, among other things, an axial flux electric machine incorporating a plurality of stator structures disposed within the gap between the rotors, wherein 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 braking but cannot produce motor action or operate as a generator). Such a configuration can result in an electric machine with thermal, electrical, and mechanical properties that cannot be achieved using a single stator structure or multiple identical stator structures. In some implementations, such functionality can be achieved by arranging individual stator segments at different angular positions within the gap, relative to the axis of rotation of the machine. In other implementations, different stator structures may be arranged to at least partially overlap each other within the gap, such as by arranging individual stator structures on different layers of the same printed circuit board.

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

[0029] Figures 1 and 2 respectively show an exploded view and a cross-sectional view of a planar stator axial flux machine 100. As shown in these figures, the planar stator 102 may be installed within the magnetic circuit gap established by the rotor components. As best shown in Figure 1, the rotor may include magnets 104a, 104b and support structures 106a, 106b that together form a pair of rotor assemblies 108a, 108b that can be attached to the rotor shaft 110. As shown in Figure 2, the outer edge 112 of the stator 102 can be fixedly attached to the housing 114 (e.g., by being held between individual sections 114a and 114b of the housing 114), while the 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 that rotates synchronously about the axis of rotation of the rotor can be imposed on the stator 102 by the controller 118 (shown in Figure 1). The interaction of this current density with the magnetic flux within 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 electromechanical device 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 type of machine can simulate various mechanical loads, including components of friction, moment of inertia, and the like.

[0031] Figure 3 shows a variant of the planar axial flux machine in which the stator is not an annulus but a section 302. There can be various advantages to producing the stator in this manner, as specified in Publication No. '361, including that the machine can be designed for higher manufacturing efficiency and / or to be suitable for loads that are effectively periodic. This can be particularly advantageous when the radius of the machine is large.

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

[0033] Figures 4 and 5 show, respectively, an exploded view and a cross-sectional view of one possible configuration of such a planar axial flux machine 400. In the illustrated embodiment, the machine 400 includes four stator segments 402a, 402b, 404a, 404b that are offset from each other at an angle with respect to the axis of rotation of the rotor. In other implementations, the machine 400 may alternatively have additional or fewer segments.

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

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

[0036] FIG. 7 shows a first exemplary implementation of a planar axial flux machine 700 that includes a plurality of different stator structures types, as described in relation to FIGS. 4 - 6. Similar to FIG. 6, the upper rotor assembly 108a is not depicted in FIG. 7 to enable a clear view of the two exemplary stator compartments 702, 704 included within the machine 700. Only the two stator compartments 702, 704 are shown in FIG. 7, but as previously mentioned, one or more additional stator compartments of either or both of the types shown, and / or one or more additional compartments of different types (such as those described herein) may be employed in other implementations.

[0037] As shown in FIG. 7, compartment 702 and compartment 704 may each include one or more windings 706. In some implementations, the windings 706 of compartment 702 may be electrically insulated from the windings 706 of compartment 704 and may have substantially different electrical characteristics. In the illustrated embodiment, for example, compartment 702 includes windings 706a, 706b, and 706c for three individual phases, and such phase windings form a total of four turns, whereas compartment 704 includes windings 706d, 706e, and 706f for three individual phases, and such phase windings form a total of two turns.

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

[0039] Similarly, in an embodiment where the windings 706d, 706e, 706f of section 704 are connected to the terminals 406d, 406e, 406f using a "Y" configuration (e.g., the figure described in FIG. 8A), two of the windings 706 will be identified between each individual pair of terminals 406d, 406e, 406f. In an embodiment where the windings 706d, 706e, 706f of section 704 are connected to the terminals 406d, 406e, 406f using a "Δ" configuration (e.g., the figure described in FIG. 8B), each individual pair of terminals 406d, 406e, 406f will identify one winding 706 that is connected in parallel in combination with two other windings 706 connected in series. In an embodiment where the windings 706d, 706e, 706f of section 704 are connected to three separate pairs of terminals (e.g., the figure described 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 magnet, as observed between a given set of terminals, will depend on the area swept by the rotation of winding 706 as observed by those terminals, and the amount of flux from the rotor captured by those areas. Thus, for any such terminal configuration, the flux linkage enabled by winding 706 of section 702 as observed between a given pair of terminals 406 of section 702 will likely be substantially different from the flux linkage enabled by winding 706 of section 704 as observed between a given pair of terminals 406 of section 704. The different electrical characteristics of the windings 706 of the two stator sections 702, 704 may allow the individual stator sections 702, 704 to be configured for significantly different operating regimes, e.g., optimal performance under torque and speed. In this manner, the stator sections 702, 704 may rely on the same magnetic structure and assembly for energy conversion in complementary operating conditions for which they are designed.

[0041] As shown in FIG. 7, compartment 702 may include a plurality of terminals (e.g., terminals 406a, 406b, and 406c) that may be connected to controller 118a. Similarly, compartment 704 may include a plurality of terminals (e.g., terminals 406d, 406e, and 406f) that may be connected to controller 118b. Controllers 118a, 118b may each include, for example, a set of switches, such as metal-oxide-semiconductor field-effect transistor (MOSFET) switches, and a control circuitry configured to selectively turn on and control those switches to achieve the functionality described herein. As shown in FIG. 7, in some implementations, controller 118a may further be connected to a power source (or energy storage unit) 708a, and controller 118b may further be connected to a power source (or energy storage unit) 708b. In some implementations, power source (or energy storage unit) 708a may be separate from 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 an implementation where the controller 118a is connected to a power source, the controller 118a may selectively apply power signals of multiple phases to windings 706a, 706b, and 706c in section 702. Similarly, in an implementation where the controller 118b is connected to a power source, the controller 118b may selectively apply power signals of multiple phases to windings 706d, 706e, and 706f in section 704. In an implementation where the controller 118a is connected to an energy storage unit, the controller 118a may instead adjust the supply of power from windings 706a, 706b, and 706c to the energy storage unit 708a. Similarly, in an implementation where the controller 118b is connected to an energy storage unit, the controller 118b may instead adjust the supply of power from windings 706d, 706e, and 706f to the 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 characteristics, and other sections (e.g., section 704) may be configured as a generator having windings 706 with a second different set of electrical characteristics. 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 characteristics, and other sections (e.g., section 704) may also be configured as a motor, but may have windings 706 with a second different set of electrical characteristics. In still 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 characteristics, and other sections (e.g., section 704) may also be configured as a generator, but may have windings 706 with a second different set of electrical characteristics.

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

[0044] FIGS. 8A - C illustrate three possible schemes for driving (or receiving power from) three windings (i.e., windings W1, W2, and W3) via a plurality of terminals. The schemes shown in FIGS. 8A and 8B allow for the use of only three terminals (i.e., terminals T1, T2, and T3) to drive (or receive power from) three windings (i.e., windings W1, W2, and W3) for 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) three windings (i.e., windings W1, W2, and W3) for 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. Either of the foregoing configurations may be used to interconnect the windings 706 and the terminals 406 of the individual stator segments 702, 704 shown in FIG. 7, and if the configuration of FIG. 8C is employed for any such segment, additional terminals may be provided.

[0045] Regarding the implementation of a 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 conceivable. (1) Windings W1, W2, and W3 in FIG. 8A may correspond to windings 706a, 706b, and 706c for three phases of the stator section 702 shown in FIG. 7, and terminals T1, T2, and T3 in FIG. 8A may correspond to three terminals 406a, 406b, and 406c of the stator section 702 shown in FIG. 7. (2) Windings W1, W2, and W3 in FIG. 8A may correspond to windings 706d, 706e, and 706f for three phases of the stator section 704 shown in FIG. 7, and terminals T1, T2, and T3 in FIG. 8A may correspond to three terminals 406d, 406e, and 406f of the stator section 704 shown in FIG. 7. (3) Windings W1, W2, and W3 in FIG. 8B may correspond to windings 706a, 706b, and 706c for three phases of the stator section 702 shown in FIG. 7, and terminals T1, T2, and T3 in FIG. 8B may correspond to 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 three phases of the stator section 704 shown in FIG. 7, and terminals T1, T2, and T3 in FIG. 8B may correspond to three terminals 406d, 406e, and 406f of the stator section 704 shown in FIG. 7.

[0046] In any of the foregoing configurations, due to the different winding configurations (e.g., different number of turns per winding) of the stator segments 702, 704, between any two of the terminals 406a, 406b, and 406c of the stator segment 702, values of various electrical characteristics (e.g., resistance, magnetic flux linkage, etc.) as measured when those terminals are not connected to an external circuit network will be substantially different from the values of those same electrical characteristics as also measured between any two of the terminals 406d, 406e, and 406f of the stator segment 704 when those terminals are not connected to an external circuit network. As used herein, a difference is considered "substantial" if it is greater than what would be expected due to standard manufacturing tolerances.

[0047] FIG. 9 shows a second exemplary implementation of a planar axial flux machine 900 that includes a plurality of different stator structure types, as described in connection with FIGS. 4 - 6. Only two stator segments 902, 904 are shown in FIG. 9, but it should be understood that one or more additional stator segments of either or both of the types shown, and / or one or more additional segments of different types, may be employed in other implementations. Similar to the case of FIG. 7, the upper rotor assembly 108a is not depicted in FIG. 9 in order to allow a clear view of the two exemplary stator segments 902, 904 included within the machine 900.

[0048] As shown, the stator section 902 of machine 900 may have one or more windings 706 that are connected to controller 118 via one or more terminals 406, and the controller 118 is in turn connected to a power source (or energy storage unit) 708, and thus the section 902 may be configured similarly to the stator section 702 (or stator section 704) shown in FIG. 7 in that it can operate in either motor or generator mode. However, the section 904 of machine 900 can be a conductive sheet of material (e.g., aluminum or copper) positioned within the gap in the active region of machine 900, and thus, as the rotor rotates, eddy currents are generated, which can cause the generation of 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 region such that eddy currents can be induced within the structure, and thus includes conductive planar structures with holes or other discontinuities (e.g., planar mesh structures), as well as conductive planar structures without such discontinuities, e.g., continuous aluminum or copper sheets.

[0049] Advantageously, the drag force introduced through section 904 is either selectively complemented or selectively counteracted by operating controller 118 appropriately, and thus the motor or generator behavior of section 902 can potentially allow for fine-tuning of the level of drag force imposed on the rotor of machine 900. The combination of stator section 902 with stator section 904 in such a structure can thus operate as an eddy current damper with programmable dynamics through the motor or generator action of stator 902. In some implementations, the overall drag coefficient of such a damper can additionally or alternatively be varied by adjusting the extent to which stator section 904 protrudes into the gap of machine 900. Machine 900 can find useful applications in scenarios where an adjustable level of drag force is desirable, such as for stationary cycling machines or other exercise equipment.

[0050] Figure 10 is a partial cutaway view showing a third exemplary implementation of the planar axial flux machine 1000 that includes a plurality of different stator structures types. Again, the upper rotor assembly 108a is not depicted in FIG. 10 to enable a clear view of the different stator structure types included within the machine 1000. As shown in FIG. 10, the machine 1000 may include a section 1002 (and associated circuitry 118, 708) that is the same as, or similar to, the section 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 section 1002 in motor mode or generator mode. However, the machine 1000 differs from the machine 900 (shown in FIG. 9) in that the machine includes an annular sheet 1004 of conductive material (e.g., aluminum or copper) that extends throughout the active region of the machine 1000, including the region directly below the section 1002, for example, on a different layer than the windings 706 of the section 1002. Similar to the section 904 of the machine 900, as the rotor of the machine 1000 rotates, eddy currents are generated within the annular sheet 1004 of the machine 1000, and thus can cause the generation of drag force on the rotor that increases as a function of the rotor speed. Similar to the machine 900, the drag force introduced through the annular conductive sheet 1004 can either be selectively compensated for or selectively counteracted by operating the controller 118 appropriately, and thus may enable the motor or generator behavior of the section 1002 to finely tune the level of drag force imposed on the rotor of the machine 1000.

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

[0052] FIG. 11 shows an example of a planar axial flux machine 1100 having a novel compartment configuration that can be employed either alone or in combination with one or more additional or different compartment structures. As shown, the machine 1100 may include a compartment 1102 that includes one or more windings 1104 connected to a controller 1106 via two or more terminals 1108. The controller 1106 may include, for example, one or more switches, such as MOSFET switches, and a control network configured to selectively turn on and control such switches to achieve the functionality described herein. 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, the switches of the controller 1106b may be selectively closed to connect a dissipative element between a pair of terminals 1108 that are connected to individual ends of the winding 1104. By interconnecting the ends of the winding 1104 in such a manner, the movement of the rotor can cause eddy currents to circulate through the winding 1104 and the dissipative element 1110, and thus generate 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 enable the magnitude of such drag force to be adjusted. Thus, in some implementations, the switches of the controller 1106 may be rapidly turned on and off at different rates to adjust the average value of the resistance measured 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 (either directly or via one or more dissipative elements 1110) a connection between a pair of terminals that are electrically connected to the ends of the individual windings 1104. In such embodiments, the amount of drag force imposed on the rotor of the machine 1100 may, in addition or alternatively, be adjusted by modifying some of the individual windings 1104 to which such a connection is established. Only one section 1102 is shown in FIG. 11, but 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 shows a fourth exemplary implementation of a planar axial flux machine 1200 that includes a plurality of different stator structure types, as described in connection with FIGS. 4-6. Similar to other embodiments, the upper rotor assembly 108a is not depicted in FIG. 12 to enable a clear 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 that are 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 that are 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 force generating component) for the rotor of the machine 1200. Only two stator sections 1202, 1204 are shown in FIG. 12, but as previously mentioned, 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.

[0055] As shown in FIG. 12, compartments 1202 and 1204 may each include one or more windings 706, 1104. In some implementations, the winding 1104 of compartment 1202 may be electrically insulated from the winding 706 of compartment 1204 and may have substantially different electrical characteristics. In the illustrated embodiment, for example, compartment 1204 includes windings 706a, 706b, and 706c for three individual phases, and such phase windings form a total of four turns, while compartment 1202 includes only one winding 1104 that forms a total of eight turns.

[0056] In an embodiment where the windings 706a, 706b, 706c of compartment 1204 are connected to terminals 406a, 406b, 406c using a "Y" configuration (e.g., the figure described 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 compartment 1204 are connected to terminals 406a, 406b, 406c using a "Δ" configuration (e.g., the figure described in FIG. 8B), each individual pair of terminals 406a, 406b, 406c will identify one winding 706 that is connected in parallel in combination with two other windings 706 connected in series. In an embodiment where the windings 706a, 706b, 706c of compartment 1204 are connected to three separate pairs of terminals (e.g., the figure described 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, as is seen between a given set of terminals, the flux linkage with the rotor magnet will depend on the area swept by the rotation of winding 706 as confirmed by those terminals, and the amount of flux from the rotor captured by those areas. Thus, in the case of any such terminal configuration, the flux linkage enabled by winding 1104 of section 1202, as is seen between terminals 1206a, 1206b, will be substantially different from the flux linkage enabled by winding 706 of section 1204, as is seen between individual pairs of terminals 406. The different electrical characteristics of windings 1104, 706 of the two stator sections 1202, 1204 may thus enable each individual stator section to be configured to perform its individual functions (e.g., motor / generator action and braking action) in an optimal manner.

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

[0059] FIG. 13 shows a fifth exemplary implementation of a planar axial flux machine 1300 that includes a plurality of different stator structures types, as described in connection with FIGS. 4 - 6. Again, the upper rotor assembly 108a is not depicted in FIG. 13 to enable a clear view of the two exemplary stator structures 1302, 1304 included within machine 1300. As shown, 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 machine 1100 (shown in FIG. 11), and (B) a conductive sheet of material (e.g., aluminum or copper) positioned within the airgap in the active region of machine 1300 such that eddy currents are generated as the rotor rotates, and thus, can cause the generation of drag force on the rotor that increases as a function of rotor speed. In some implementations, the stator section 1302 and associated circuitry 1106, 1110 may operate to selectively complement the drag force imposed on the rotor of machine 1300 via stator section 1304, and thus, may enable fine - tuning of the level of drag force imposed on the rotor of machine 1300. Only two stator sections 1302, 1304 are shown in FIG. 13, but 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 different types, may be employed in other implementations.

[0060] FIG. 14 is a partial cutaway view showing a sixth exemplary implementation of a planar axial flux machine 1400 that includes a plurality of different stator structures. Again, the upper rotor assembly 108a is not depicted in FIG. 14 to enable a clear view of the two exemplary stator structures 1402, 1404 included within machine 1300. As shown, 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 machine 1100 (shown in FIG. 11), and (B) a conductive material (e.g., aluminum or copper) annular sheet 1404 positioned within the airgap in the active region of machine 1400 such that eddy currents are generated as the rotor rotates and thus a drag force on the rotor that increases as a function of rotor speed can be generated.

[0061] Similar to machine 1300 (shown in FIG. 13), in some implementations, the stator section 1402 and associated circuitry 1106, 1110 operate to selectively complement the drag force imposed on the rotor of machine 1300 via the annular conductive sheet 1404, and thus may enable fine-tuning of the level of drag force imposed on the rotor of machine 1400. Only two stator structure types are shown in FIG. 14, but 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 different types, may be employed in other implementations.

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

[0063] For other exemplary embodiments described above, similar performance can be obtained by connecting a controllable eddy current brake on the same shaft as the motor. Again, such a solution would increase the complexity and cost of the system. In particular, additional magnetic structures would be required for the braking characteristics. For example, an electromagnet that requires an external power source, or additional magnets that are only used when braking. The use of some of the stator machine configurations described herein would, as before, obviate these considerations.

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

[0065] The mechanical embodiments of the type described here are suitable for several application areas, and the examples include, but are not limited to, the following.

[0066] One application is in therapy or exercise equipment. Here, the role of the machine is to resist the force applied by a human while simulating a target activity, absorb a portion of that applied force, or convert it into power. Such activities can include the force and inertia characteristics of lifting a barbell, the drag force when rowing a boat, the variable resistance associated with cycling, etc. The dynamics required to simulate these activities can be achieved, for example, through the feedback control of a conventional servo motor combined with an energy storage and dissipation mechanism. The use of some of the stator machine configurations described herein would allow the motor action to be integrated with a dissipative stator element, with the advantages including a reduction in the overall system cost and complexity.

[0067] In some implementations, multiple motor stator structures may be combined within the gap, in addition to, or as an alternative to, meeting the wide 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 be combined, in addition to, or as an alternative to, with a section specialized for induction 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 adjusts the turbine speed under strong wind conditions. In a similar motor application, the braking section may provide an emergency shaft stop function.

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

[0070] (P1)A planar stator for an axial flux machine having a rotor that includes one or more magnets that generate a first magnetic flux substantially parallel to the axis of rotation of the rotor within an active region within the air gap of the axial flux machine, the planar stator comprising at least first, second, third, and fourth terminals, each adapted to be connected to an external network of the planar stator, at least one first winding arranged to be positioned within the active region, the at least one first winding having first and second ends each electrically connected to the first and second terminals, the electrical characteristics between the first and second terminals as measured when the first and second terminals are not connected to the network having a first value, at least one first winding, and at least one second winding arranged to be positioned within the active region, the at least one second winding being electrically insulated from the at least one first winding and having third and fourth ends each electrically connected to the third and fourth terminals, the electrical characteristics between the third and fourth terminals as measured when the third and fourth terminals are not connected to the network having a second value substantially different from the first value, may include at least one second winding.

[0071] (P2)The planar stator may be configured as described in paragraph (P1), 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 offset at an angle from the first stator section with respect to the axis of rotation.

[0072] (P3) The planar stator may be configured as described in paragraph (P1) or paragraph (P2). The at least one first winding may include a first winding and at least one additional winding. The circuit network may include a power source. The first winding may be configured to support a first phase from the power source. The at least one additional winding may be configured to support 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 with respect to the axis of rotation.

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

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

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

[0076] (P7) The planar stator may be configured as described in any of paragraphs (P1)-(P6), and the circuit network further includes a second controller configured to selectively couple the third and fourth terminals to a power source. Thus, during at least a second operating mode of the axial flux machine, at least one second winding may generate a third magnetic flux substantially 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 and fourth terminals when at least one second winding is not coupled to an external power source.

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

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

[0080] (P11) The planar stator may be configured as described in any of paragraphs (P1)-(P10), and the circuit network may further include a second controller configured to selectively couple the third and fourth terminals to an energy storage element. Thus, 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 circuit network further comprises a first controller configured to selectively couple the first and second terminals to an energy storage element. Thus, 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 circuit network further comprises a second controller configured to selectively couple the third and fourth terminals to an energy storage element. Thus, 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 and second terminals when at least one of the first windings is not coupled to an external power source.

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

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

[0086] (For an axial flux machine having a rotor including one or more magnets that generate a first magnetic flux substantially parallel to the axis of rotation of the rotor within the active region within the gap of the axial flux machine) The planar stator for the axial flux machine includes a first conductive sheet arranged to be positioned within the active region such that the generation of eddy currents within the first conductive sheet imposes a drag force on the rotor, and at least a first winding arranged to be positioned within the active region, 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, and thus, during at least a first operating mode of the axial flux machine, the first winding may generate a second magnetic flux substantially 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 an energy storage element, and thus, 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.

[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 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 at least one switch may be configured to selectively establish an electrical connection between the first terminal and the second terminal via at least one dissipative element.

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

[0092] (P23) For an axial-flux machine having a rotor including one or more magnets that generate a first magnetic flux substantially parallel to the axis of rotation of the rotor within the active region within the gap of the axial-flux machine, a planar stator is at least a first winding arranged to be positioned within the active region, the first winding having at least first and second terminals that are 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 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 at least one switch may further be configured to establish an electrical connection between the first terminal and the second terminal via 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 at least one switch to control the time-average conductivity between the first terminal and the second terminal.

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

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

[0097] (P28)The plate of conductive material is the machine described in paragraph (P27) that can be moved radially into or out of the gap.

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

[0099] (P30)The planar stator section is exchangeable, for the machine described in any one of paragraphs (P26)-(P29).

[0100] (P31)At least one stator section and at least one conductive plate are arranged around the axis of rotation, for the machine described in any one of paragraphs (P26)-(P30).

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

[0102] (P33)The conductive plate and the stator section are configured to be exchangeable, for the machine described in any one of paragraphs (P26)-(P32).

[0103] Some aspects of at least one embodiment have been described as above, but it should be understood that various modifications, corrections, and improvements will readily occur to those skilled in the art. Such modifications, corrections, and improvements are intended to be part of this disclosure and are intended to be within the spirit and scope of this disclosure. Therefore, the foregoing description and drawings are merely examples.

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

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

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

[0107] Also, the terminology and technical terms used herein are for the purpose of explanation and should not be considered limiting. The use of "including," "comprising," "having," "containing," "accompanying," and variations thereof herein is meant to include the listed items and their equivalents and additional items.

[0108] The claimed subject matter is as follows.

Claims

Claim 1. An apparatus, comprising: a rotor configured to rotate about a rotation axis, the rotor including one or more magnets that generate a first magnetic flux within an active region; a first conductive sheet positioned within the active region such that generation of eddy currents within the first conductive sheet imposes a drag force on the rotor; a stator structure including at least a first winding positioned within the active region; at least first and second terminals, the first and second terminals being connected to different portions of the first winding such that (A) application of a current between the first terminal and the second terminal causes the first winding to generate a second magnetic flux within the active region, or (B) magnetic flux linkage between the first winding and the one or more magnets while the rotor is rotating generates a voltage between the first terminal and the second terminal; at least a first switch configured and arranged to selectively couple one or more circuit components between the first terminal and the second terminal, thereby regulating flow of current through the first winding; a control circuit configured to adjust a manner in which the first switch operates to selectively couple the one or more circuit components between the first terminal and the second terminal, thereby selectively compensating for or reacting against the drag force on the rotor; and the apparatus comprises the above components. Claim 2. The stator structure has a substantially planar shape. The apparatus is an axial flux machine, in which the one or more magnets generate the first magnetic flux substantially parallel to the rotation axis within a gap in which the stator structure is positioned. The apparatus according to claim 1. Claim 3. The one or more circuit components include a power source. The control circuit is configured to operate the first switch to selectively couple the first winding between the first terminal and the second terminal such that the first winding generates the second magnetic flux substantially parallel to the rotation axis during at least a first operating mode of the axial flux machine. The apparatus according to claim 2. Claim 4. The one or more circuit components include an energy storage element. The control circuit is configured to operate the first switch to selectively couple the energy storage element between the first terminal and the second terminal 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. The apparatus according to claim 2.

5. The one or more circuit components include a conductor. The first switch is configured and arranged to be selectively closed to establish an electrical connection between the first terminal and the second terminal via the conductor at a time when the first winding is not coupled to an external power source. The apparatus according to claim 2.

6. The one or more circuit components include at least one dissipative element. The first switch is further configured and arranged to selectively couple the at least one dissipative element between the first terminal and the second terminal. The apparatus according to claim 2.

7. The control circuit is further configured to cause the first switch to be modulated to control a time-average conductivity between the first terminal and the second terminal. The apparatus according to claim 6.

8. The control circuit is further configured to cause the first switch to be modulated to control a time-average conductivity between the first terminal and the second terminal. The apparatus according to claim 5.

9. The one or more circuit components include a power source. The control circuit is configured to operate the first switch to selectively couple the power source between the first terminal and the second terminal such that, during at least a first operating mode of the apparatus, the first winding generates the second magnetic flux. The apparatus according to claim 1.

10. The one or more circuit components include an energy storage element. The control circuit is configured to operate the first switch to selectively couple the energy storage element between the first terminal and the second terminal such that, during at least a first operating mode of the apparatus, the energy storage element receives power generated by the first winding in response to rotation of the rotor. The apparatus according to claim 1. **Claim 11**: The one or more circuit components include a conductor, wherein the first switch is configured and arranged to be selectively closed to establish an electrical connection between the first terminal and the second terminal via the conductor at a time when the first winding is not coupled to an external power source. The apparatus according to claim 1. **Claim 12**: The one or more circuit components further include at least one dissipative element, wherein the first switch is further configured and arranged to selectively couple the at least one dissipative element between the first terminal and the second terminal. The apparatus according to claim 1. **Claim 13**: The control circuit is further configured to cause the first switch to be modulated to control a time-average conductivity between the first terminal and the second terminal. The apparatus according to claim 12. **Claim 14**: The control circuit is further configured to cause the first switch to be modulated to control a time-average conductivity between the first terminal and the second terminal. The apparatus according to claim 11. **Claim 15**: A method of operating the apparatus according to claim 1, operating the first switch in a first mode to complement or counteract the drag force on the rotor by a first amount by using the control circuit; operating the first switch in a second mode to complement or counteract the drag force on the rotor by a second amount different from the first amount by using the control circuit A method comprising. **Claim 16**: The method according to claim 15, further comprising adjusting the position of the first conductive sheet relative to the active region so as to change the drag force. **Claim 17**: A method of operating the apparatus according to claim 2, operating the first switch in a first mode to complement or counteract the drag force on the rotor by a first amount by using the control circuit; operating the first switch in a second mode to complement or counteract the drag force on the rotor by a second amount different from the first amount by using the control circuit A method comprising. The method according to claim 17, further comprising adjusting the position of the first conductive sheet with respect to the active region so as to vary the resistance. Claim 19. The one or more circuit components include a power source. Operating the first switch in the first mode by using the control circuit includes operating the first switch to selectively couple the power source between the first terminal and the second terminal so that the first winding generates a first amount of the second magnetic flux substantially parallel to the axis of rotation. Operating the first switch in the second mode by using the control circuit includes operating the first switch to selectively couple the power source between the first terminal and the second terminal so that the first winding generates a second amount of the second magnetic flux substantially parallel to the axis of rotation. The method according to claim 17, wherein the second amount is different from the first amount. Claim 20. The one or more circuit components include at least one dissipative element. Operating the first switch in the first mode by using the control circuit includes modulating the first switch to selectively couple the at least one dissipative element between the first terminal and the second terminal so that a first time-average conductivity is established between the first terminal and the second terminal. Operating the first switch in the second mode by using the control circuit includes modulating the first switch to selectively couple the at least one dissipative element between the first terminal and the second terminal so that a second time-average conductivity different from the first time-average conductivity is established between the first terminal and the second terminal, the method according to claim 17.

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