electric motor

Abstract

To provide a magnetically induced motive force aligned in a movement direction by a greater component.SOLUTION: An electric motor has a stator having multiple stator poles with associated electrical windings, and a rotor having multiple rotor poles. The rotor has flux barriers between adjacent rotor poles, the flux barriers each having a material with an electrical conductivity higher than that of the rotor pole material. The flux barriers are electrically isolated from one another external to the ferromagnetic material. Eddy currents are induced in the flux barrier to cause destructive interference of an impending magnetic field, such that the flux barrier effectively acts to inhibit magnetic flux during motor operation, which in some cases will result in a repulsive force that will act to increase an induced motive force on the rotor poles.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 715,386, filed August 7, 2018, the entire disclosure of which is incorporated herein by reference.

[0002] Technical Field The present invention relates to electric motors and the operation of such motors. [Background technology]

[0003] background Two ways in which the performance of electric motors can be characterized are by their torque / force and their power output. The power output of a rotary motor is the product of the torque the motor generates and the angular velocity of its output shaft. For a linear motor, power output is the product of linear force and speed. Traditionally, there are two basic means of directly increasing motor performance: (1) increasing the motor's size and (2) generating a stronger magnetic field within the motor itself. While the final size of a motor limits its particularly useful applications, increasing the magnetic field, and thereby increasing the electromagnetic force, can be considered important in enabling better motor performance and wider application of motor technology. There is a need for new motor designs that provide acceptably high performance (e.g., high torque / force and power density) in a compact package that enables direct drive applications. Summary of the Invention [Means for solving the problem]

[0004] overview Various aspects of the present invention feature electric motors having magnetic flux barriers positioned between passive poles to redirect magnetic flux to provide a larger component of magnetically induced power aligned with the direction of motion (to provide useful torque and / or linear force).

[0005] According to one aspect of the present invention, an electric motor includes a stator having a plurality of stator poles and electrical windings associated with the stator poles, and a rotor having a plurality of rotor poles. The rotor is movable relative to the stator and defines, together with the stator, a nominal gap between the stator poles and the rotor poles. The rotor poles are a stack of layers of ferromagnetic material separated from one another at least at the rotor surface by interfaces that are less electrically conductive than the ferromagnetic material. The rotor has magnetic flux barriers between adjacent rotor poles, each of which comprises a material having a higher electrical conductivity than the ferromagnetic material. The magnetic flux barriers are electrically insulated from one another outside the ferromagnetic material.

[0006] As used herein, the term "electric motor" also includes generators that produce electrical power from mechanical power.

[0007] "Nominal gap" means the gap between the relative moving surfaces of the stator (or active magnetic component) poles and the rotor (or passive magnetic component) poles across which magnetic flux extends during motor operation to induce a force on the rotor (or passive magnetic component). We use the term "active magnetic component" to refer to the portion of the motor that includes the electrical windings associated with their respective magnetically permeable structures (magnetic flux is generated by current flowing in the windings). The poles of an "active magnetic component" are called "active poles." The electrical windings will typically be held in a fixed relationship to the corresponding active poles. A wound stator is an example of an active magnetic component. The magnetic flux in the passive magnetic component across the nominal gap We use the term "passive magnetic component" to refer to the portion of the motor in which motive force is induced by the magnetic flux generated by the active magnetic component to extend into the rotor. The poles of a "passive magnetic component" are called "passive poles." An unwound rotor is an example of a passive magnetic component. The nominal gap may be, for example, radial, as in a radial gap motor, or axial, as in an axial gap motor, and may be filled with air or other gas or even a liquid such as a refrigerant.

[0008] "Flux barrier" means a structure defining at least one conductive path through which current flow is induced by changing magnetic fields. Generally, eddy currents are induced in the flux barrier to cause destructive interference of steep magnetic fields, thereby effectively acting to suppress changes in magnetic flux during motor operation, producing repulsive forces that, in some cases, act to increase the induced motive force on the passive pole.

[0009] "Conductive" refers to the tendency of a material to conduct electricity. With respect to a structure such as a wire in which current is constrained to flow in a primary direction, "conductive" refers to electrical conductivity in the primary direction.

[0010] "Electrically isolated from one another" means that the ohmic resistance to potential within the flux barrier is at least 10 times lower than the ohmic resistance between the flux barriers. The fact that the flux barriers are isolated from one another outside the ferromagnetic object does not exclude the flux barriers being in electrical communication through the ferromagnetic material of the layer. In fact, in many cases, the flux barriers are electrically connected through the ferromagnetic material.

[0011] In some embodiments, at least some of the flux barriers each include a conduction band spanning multiple interfaces of the stack of layers.

[0012] "Conductive" means that the material or structure is at least as conductive as amorphous carbon or has a conductivity greater than 1000 siemens / meter at typical motor operating voltages. Examples of conductive materials include silver, copper, aluminum, nickel, iron, and electrical steel (grain-oriented or not). Examples of non-conductive materials include unfilled resin, air, wood, and cotton. We use the term "insulator material" to refer to materials that are non-conductive, i.e., do not conduct electricity.

[0013] In some examples, the conductive band comprises at least 20%, in some cases 40%, or in some cases 60% by mass of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt. In some cases, each of the flux barriers having a conductive band also has a conductive layer of a different material than the conductive band and at least partially forms the outer surface of the rotor.

[0014] In some configurations, the conductive band comprises at least 1%, in some cases 5%, or in some cases 15%, by mass fraction of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes.

[0015] The conductive bands may have or consist of discrete layers that run parallel to the nominal gap and form interlayer interfaces of various materials, in some cases one of the various materials comprising or consisting essentially of copper and another of the various materials comprising or consisting essentially of nickel.

[0016] In many cases, the conductive band has an exposed surface facing the nominal gap.

[0017] In some motors, each of the flux barriers having conductive bands includes at least two conductive bands electrically connected to each other at opposite ends of the stack of layers to form a conductive loop.

[0018] In some embodiments, at least some of the flux barriers each have a shape, in a cross section taken parallel to the ferromagnetic material layers of the stack of layers, that includes two spaced apart protrusions extending away from the nominal gap and a surface layer connecting the two protrusions, The two protrusions may be located, for example, on opposite sides of a portion of the stack of ferromagnetic material layers.

[0019] In some embodiments, at least some of the flux barriers each have a conductive layer of constant width in the direction of relative motion between the rotor and stator and constant thickness perpendicular to the nominal gap that intersects multiple interfaces of the stack of layers and has an exposed surface that forms a surface of the rotor at the gap.

[0020] "Constant width" means that the layer has edges, but does not extend around the entire circumference of, for example, a rotor (or along the entire length of a linear passive magnetic component).

[0021] Similarly, "constant thickness" means that the layer extends to a limited depth but does not penetrate completely through, for example, the rotor.

[0022] In some cases, the width of the layer is more than twice the thickness of the layer, in some cases more than five times, and in some cases more than ten times.

[0023] In some motors, the layers are formed of a material that has a current skin depth greater than the layer thickness at motor operating conditions.

[0024] "Current skin depth" refers to the depth below the surface of a conductor where electrical currents, particularly eddy currents induced from a changing magnetic field at a given frequency, primarily flow. For a given material, the skin depth can be calculated as follows:

number

[0025] "Magnetic permeability" generally refers to the ability of a material to support the formation of a magnetic field. The magnetic permeability of a material may be determined according to ASTM A772. When a material is said to be "magnetically permeable," it means that the material has a magnetic permeability of at least 1.3 x 10 -6 It means that it has a permeability of henry / meter.

[0026] In some examples, the layer may be disposed within a channel defined by the ferromagnetic material and may be in electrical contact with the ferromagnetic material of multiple plates or all of the plates.

[0027] In some cases, the nominal gap is thinner at the layer than near the layer.

[0028] In some embodiments, each flux barrier includes a conductive material that forms a loop around a core of core material that is more magnetically permeable (i.e., has a higher magnetic permeability) than the conductive material. In some cases, the core material is also ferromagnetic. For example, both the core material and the ferromagnetic material of the rotor poles may form adjacent portions of a laminated stack of plates.

[0029] In some arrangements, the loops form a portion of the rotor's outer surface that bounds the nominal gap. The core may form a portion of the rotor's outer surface that is surrounded by the loops.

[0030] In some cases, the loop is located below the surface of the rotor that bounds the nominal gap and includes the edge of the layer of ferromagnetic material.

[0031] In some motors, the loop defines a capacitance that can be formed at discrete locations along the loop, such as by non-conductive breaks in the loop.

[0032] The loop preferably has a resonant frequency within the range of propagation of the ferromagnetic material.

[0033] "Propagation range" means the frequency range over which the permeability drops by 10 dB or less relative to the permeability at 60 Hz, as measured under static frequency conditions (e.g., by permeability measurements at a given frequency taken over at least 5 cycles of an applied magnetic field).

[0034] In many motors, the interface between the layers of the stack consists of an oxidized surface of ferromagnetic material. In some other motors, the interface includes sheets of insulating material, such as sheets of resin film, interleaved with ferromagnetic layers.

[0035] In many embodiments, the rotor is located within the stator, while in other embodiments, the rotor poles are located outside the stator poles.

[0036] In some motors, the nominal gap is a radial gap bounded at least in part by the radially outer surface of the rotor, while in other motors, the nominal gap is an axial gap perpendicular to the rotor's axis of rotation.

[0037] In some motors, each rotor pole (and / or each stator pole) has multiple teeth defining recesses therebetween.

[0038] In some embodiments, each stator pole has flux shields extending along opposite edges of the stator pole and formed of a material having a higher electrical conductivity than the material of the stator pole disposed between the flux shields.

[0039] According to another aspect of the invention, an electric motor includes a passive magnetic component having a first surface defining a plurality of active poles having associated electrical windings, and a second surface movable in a first direction relative to the first surface and spaced apart from the first surface to define a gap. The second surface forms a series of spaced apart passive poles of a first material defining slots therebetween, the slots extending at a non-zero angle in the first direction. Each slot includes a respective flux barrier comprising a second material extending along the slot and forming a conductive path along the slot. The flux barriers are fixed to the first material within the slot and are connected to each other only through the first material.

[0040] In some embodiments, the slots extend perpendicular to the first direction (ie, the non-zero angle is 90 degrees).

[0041] In some cases, the flux barrier fills the slot.

[0042] In some motors, the flux barriers are in contact (preferably electrical contact) with the first material on either side of the slot.

[0043] In some configurations, the flux barrier has an exposed surface that forms part of the second surface.

[0044] In some motors, the passive poles include edge surface regions of a stack of plates stacked such that the slots intersect some of the plates in the stack. Preferably, the second material of each flux barrier intersects some of the plates in the stack and / or is in direct contact with each of the plates in the stack.

[0045] The second material preferably has a higher electrical conductivity than the first material.

[0046] In some examples, each of the flux barriers consists essentially of the second material.

[0047] In some cases, the second material comprises at least 20%, in some cases 40%, or in some cases 60%, by mass fraction of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt.

[0048] In some examples, each of the flux barriers includes a conductive layer of a second material and a conductive layer of a third material that at least partially forms the outer surface of the rotor.

[0049] In some embodiments, the second material comprises at least 1%, in some cases 5%, or in some cases 15%, by mass fraction of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes.

[0050] In some configurations, each flux barrier includes multiple discrete layers that extend parallel to the nominal gap and form interlayer interfaces of various materials, in some examples, one of the various materials includes or is copper, and another of the various materials includes or is nickel.

[0051] In some embodiments, at least some of the magnetic flux barriers each have a cross-sectional shape that includes two spaced apart protrusions extending away from the nominal gap and a surface layer connecting the two protrusions, and in some cases, each magnetic flux barrier having this cross-sectional shape further includes a magnetically permeable material disposed between the two protrusions and below the surface layer.

[0052] In some cases, the second material of each flux barrier forms a conductive loop centered on a respective core of a core material of higher magnetic permeability than the second material. The core material may be ferromagnetic. In some configurations, the core material and the first material form adjacent portions of a single stack of plates.

[0053] In some examples, the loops form a portion of the rotor's outer surface that bounds the nominal gap. For example, the core may form a portion of the rotor's outer surface that is surrounded by the loops.

[0054] In some motors, the loop bounds the nominal gap and is located below the surface of the passive magnetic component formed of a first material.

[0055] In some motors, the loop defines a capacitance that can be formed at discrete locations along the loop, such as by non-conductive breaks in the loop.

[0056] The loop preferably has a resonant frequency within the range of propagation of the first material.

[0057] In some embodiments, the active magnetic component is a stator of a motor and the passive magnetic component is a rotor of the motor. In some examples, the nominal gap is a radial gap bounded at least in part by a radially outer surface of the rotor. In other examples, the nominal gap is is the axial gap perpendicular to the rotor axis of rotation.

[0058] In some cases, each passive pole and / or each active pole has a plurality of teeth defining a recess therebetween.

[0059] In some cases, each active pole has a flux shield extending along either edge of the active pole and formed of a material having a higher electrical conductivity than the material of the stator poles disposed between the flux shields.

[0060] In some examples, the motor is a linear motor.

[0061] According to another aspect of the present invention, an electric motor includes an active magnetic component having a plurality of active poles with associated electrical windings, and a movable passive magnetic component movable relative to the active magnetic component and having a plurality of passive poles of magnetically permeable magnetic material. The active and passive magnetic components define a nominal magnetic gap between the active and passive poles. The passive magnetic component has magnetic flux barriers connecting adjacent passive poles of the passive magnetic component, each of which includes a conductive material different from the magnetically permeable pole material and defines at least one conductive path centered around a magnetically permeable core material. The magnetic flux barriers are electrically isolated from each other outside the pole material, and adjacent magnetic flux barriers are positioned such that the respective conductive path defined in the conductive material of one flux barrier does not surround a portion of the conductive path defined in the conductive material of another flux barrier.

[0062] Preferably, the core material has a higher magnetic permeability than the conductive material.

[0063] In some cases, the core material and the pole material have the same material properties.

[0064] In some examples, the flux barriers extend into adjacent pole pairs.

[0065] In some motors, the flux barriers each include at least one loop of conductive material spanning the magnetically active extent of the passive magnetic component. In some cases, each flux barrier has multiple loops of conductive material that are insulated from one another outside the pole material and core material, respectively.

[0066] In some embodiments, each magnetic flux barrier comprises at least 20%, in some cases 40%, or in some cases 60%, by mass fraction of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt.

[0067] In some cases, each flux barrier comprises at least 1%, in some cases 5%, or in some cases 15%, by mass fraction of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes.

[0068] In some examples, the core material is ferromagnetic. In some arrangements, the core material and pole material comprise adjacent portions of a single stack of plates.

[0069] The loop forms part of the outer surface of the passive magnetic component that bounds the nominal gap in some motors. The core may form part of the outer surface of the passive magnetic component that is surrounded by the loop.

[0070] The loop may be disposed below a surface of a passive magnetic component that bounds a nominal gap and is formed of a first material.

[0071] In some cases, the loop may be formed at discrete locations along the loop, such as capacitance. This defines the capacitance.

[0072] Preferably, the loop has a resonant frequency within the range of propagation of the first material.

[0073] In some embodiments, at least some of the magnetic flux barriers have exposed surfaces that intersect multiple interfaces of the stack and form surfaces of the passive magnetic component at the gap, each having a conductive layer of constant width in the direction of relative motion between the passive magnetic component and the active magnetic component and constant thickness perpendicular to the nominal gap.

[0074] In some applications, the layer width is more than two times the layer thickness, in some cases more than five times, and in some cases more than ten times.

[0075] In some cases, the layer is formed of a material that has a current skin depth greater than the layer thickness.

[0076] The layer may be disposed within a channel defined by the first material.

[0077] In some cases, the nominal gap is thinner at the layer than near the layer.

[0078] In some motors, the active magnetic component is the stator of the motor and the passive magnetic component is the rotor of the motor. The nominal gap can be a radial gap bounded at least in part by the radially outer surface of the rotor or an axial gap perpendicular to the axis of rotation of the rotor.

[0079] In some embodiments, each passive magnetic component pole and / or each active magnetic component pole has a plurality of teeth defining recesses therebetween.

[0080] In some examples, each active magnetic component has a flux shield extending along opposite edges of the pole, the flux shield being formed of a material having a higher electrical conductivity than the material of the active magnetic component disposed between the flux shields.

[0081] In some cases, the motor is a linear motor.

[0082] According to another aspect of the invention, an electric motor includes a passive magnetic component having a first surface defining a plurality of active poles having associated electrical windings, and a second surface movable relative to the first surface and spaced apart from the first surface to define a gap. The second surface has a series of spaced apart pole surface areas of a first material separated by inter-pole surface areas of the second surface. The passive magnetic component includes a second material that is electrically conductive and has a low energy product, and the magnetically permeable material defines internal paths connecting adjacent pairs of pole surface areas on either side of the respective inter-pole surface areas that are electrically insulated from one another outside the magnetically permeable material.

[0083] "Low energy product" refers to the property of a material having an energy product (B x H) of less than 100 kilojoules per cubic meter. Energy product is also understood to be the product of remanence and coercivity. Generally, permanent magnet materials used in PM motors do not have a low energy product.

[0084] In some embodiments, the magnetically permeable material forms a stack of layers of ferromagnetic material separated from one another at least in the extreme surface regions by interfaces that are less conductive than the ferromagnetic material.

[0085] In some examples, the passive magnetic component includes strips of a third material, each strip underlying a respective inter-pole surface region within the passive magnetic component and spanning the entire current suppressing interface. For example, the third material may be or may include iron, nickel and cobalt. Preferably, the third material has a higher magnetic permeability than the second material.

[0086] In some configurations, the second material extends between one side of the strip and an edge of the layer of ferromagnetic material.

[0087] In some motors, the second material has a lower magnetic permeability than the first material.

[0088] In some embodiments, the second material of at least one of the inter-pole surface regions extends from the second surface into the passive magnetic component to a total depth of about 1 to 50 mm, in some cases 2 to 25 mm, or in some cases 5 to 15 mm.

[0089] In some configurations, the second material of at least one of the inter-pole surface regions has an extent in the first direction and extends into the passive magnetic component from the second surface to a full depth of 2 to 2000% (or in some cases 5 to 500%, or in some cases 10 to 200%) of that extent.

[0090] In some cases, the second surface is movable relative to the first surface along a first direction, and the inter-pole surface area is continuous across the magnetically active extent of the pole surface area in a second direction perpendicular to the first direction.

[0091] In some motors, the magnetically permeable material forms a stack of layers of ferromagnetic material each extending in a first direction.

[0092] In some cases, the second material comprises or consists essentially of copper.

[0093] In some motors, the passive magnetic component is the rotor and the active magnetic component is the stator. The inter-pole surface area and the pole surface area may together form the cylindrical surface of the rotor, e.g., the gap is the radial gap between the rotor and the stator. Or the inter-pole surface area and the pole surface area may together form the end face of the rotor, e.g., the gap is the axial gap between the rotor and the stator. In some cases, the end face is perpendicular to the rotor's axis of rotation.

[0094] In some embodiments, the inter-pole surface regions each further include a magnetically permeable core surrounded by a second material, which in some cases is the same material as the first material.

[0095] In some examples, the polar surface regions of the second surface define a slot therebetween, and the inter-polar surface region of the second surface is formed by a second material disposed within the slot. Preferably, the slot extends at a non-zero angle (e.g., 90 degrees) relative to the direction of relative motion between the first and second surfaces. In some cases, the second material is secured to the first material within the slot. In some examples, the slot is filled with the second material and / or the second material contacts the first material on both sides of the slot.

[0096] In some examples, the polar surface regions include edge surface regions of a stack of plates stacked such that the slots intersect several plates of the stack of plates. Preferably, the second material in each slot intersects several plates of the stack and / or is in direct contact with each of the plates of the stack.

[0097] The second material preferably has a higher electrical conductivity than the first material.

[0098] In some motors, each of the inter-pole surface regions consists essentially of the second material.

[0099] The second material includes an element or combination of elements selected from the group consisting of iron, nickel, and cobalt, in some cases at a mass fraction of 20%, in some cases at a mass fraction of 40%, or in some cases at a mass fraction of 60%.

[0100] In some examples, the second material comprises at least 1%, in some cases 5%, or in some cases 15%, by mass fraction of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes.

[0101] In some embodiments, the inter-pole surface region comprises a surface of a flux barrier disposed between the pole surface regions.

[0102] In some cases, each flux barrier has discrete layers that run parallel to the nominal gap and form interlayer interfaces of various materials, such as copper and nickel.

[0103] In some examples, at least some of the magnetic flux barriers each have a cross-sectional shape that includes two spaced apart protrusions extending away from the nominal gap and a surface layer connecting the two protrusions, e.g., with a magnetically permeable material disposed between the two protrusions and beneath the surface layer.

[0104] In some configurations, the second material in each inter-pole surface region forms a conductive loop centered on a respective core of a core material having a higher magnetic permeability than the second material. In some cases, the core material is ferromagnetic. In some cases, the core material and the first material are adjacent portions of a single stack of plates. In some examples, the core forms a portion of the second surface surrounded by the loop. The loop may be spaced from the second surface and / or may define a capacitance, e.g., the capacitance is formed at a discrete location along the loop. Preferably, the loop has a resonant frequency within the propagation range of the first material.

[0105] In some motors, each pole surface area (and / or each pole of the active magnetic component) has a plurality of teeth defining recesses therebetween.

[0106] In some examples, each pole of the active magnetic component has a flux shield extending along both edges of the pole and formed of a material having a higher electrical conductivity than the material of the poles of the active magnetic component disposed between the flux shields.

[0107] In some cases, the motor is a linear motor.

[0108] According to another aspect of the invention, an electric drive system includes a reluctance motor and a motor controller. The reluctance motor includes an active magnetic component defining a plurality of active poles with associated electrical windings, and a passive magnetic component having a plurality of passive poles movable relative to the active magnetic component and defining, with the active magnetic component, a nominal gap between the active and passive poles. The motor controller has a plurality of switches connected to respective electrical windings or sets of windings of the active magnetic component, and is configured to (a) sequentially operate the switches for respective pole energization duty cycles to generate magnetic flux across the nominal gap between the active and passive poles, and (b) pulse current through the active pole winding during each active pole energization duty cycle, the pulsing including a series of at least three pulses during which adjacent active pole windings are not energized. The motor's electrical windings are configured such that the ratio of maximum current to minimum current through the energized active pole winding during current pulsing is at least 4:1.

[0109] In some embodiments, the motor controller is configured to pulse the current during the energization duty cycle of each active pole at a pulse frequency between 2 Hz and 1 MHz, in some cases between 10 Hz and 20 kHz, and in some cases between 100 Hz and 5 kHz.

[0110] In some examples, the motor controller is configured to maintain the pulse frequency during motor speed changes at least up to a motor speed where the energization duty cycle frequency per active pole is at least one-half the pulse frequency.

[0111] For some applications, the motor controller is configured to pulse the current only at motor speeds below that corresponding to one pulse per energization duty cycle.

[0112] In some cases, at least one of the electrical windings has multiple coils conductively connected in parallel and wound around a common core.

[0113] In some cases, at least one of the electrical windings is a winding of braided wire.

[0114] In some embodiments, the active magnetic component is a stator and the passive magnetic component is a rotor that is movable relative to the stator by rotation about the rotor axis. The rotor may be disposed within the stator. The nominal gap may be, for example, a radial gap bounded at least in part by the radially outer surface of the rotor or an axial gap perpendicular to the rotor axis.

[0115] In some examples, the passive magnetic component further includes flux barriers between adjacent passive poles, the flux barriers having a higher electrical conductivity than the passive poles, and the flux barriers are electrically isolated from each other outside the passive poles.

[0116] In some cases, the passive pole is formed by a stack of layers of magnetically permeable material. At least some of the magnetic flux barriers may each include a conductive band that intersects multiple layers of the stack. The conductive band comprises an element or combination of elements selected from the group consisting of iron, nickel, and cobalt, in a mass fraction of at least 20%, in some cases 40%, or in some cases 60%. Each magnetic flux barrier having a conductive band may further include a conductive layer of a material different from the current-carrying band, the conductive layer at least partially forming the outer surface of the passive magnetic component. In some examples, the conductive band comprises an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes, in a mass fraction of at least 1%, in some cases 5%, or in some cases 15%. In some configurations, the conductive band has discrete layers that extend parallel to the nominal gap and form interlayer interfaces of various materials (e.g., copper and nickel).

[0117] The conductive band may have an exposed surface facing the nominal gap.

[0118] In some cases, each of the flux barriers having conductive bands includes at least two conductive bands electrically connected to each other at opposite ends of the stack of layers to form a conductive loop.

[0119] In some embodiments, at least some of the flux barriers each have a shape in a cross section taken parallel to the layers of the stack that includes two spaced apart projections extending away from the nominal gap and a surface layer connecting the two projections. The two projections may be located on opposite sides of a portion of the stack.

[0120] In some configurations, at least some of the flux barriers intersect multiple layers of the stack and have exposed surfaces that form surfaces of the passive magnetic components at the gap. Each conductive layer has a constant width in the direction of relative motion between the magnetic components and a constant thickness perpendicular to the nominal gap. In some applications, the layer width is greater than two times the layer thickness, in some cases greater than five times, and in some cases greater than ten times.

[0121] The layer may be formed of a material having a current skin depth greater than the layer thickness and / or may be disposed within a channel defined by a magnetically permeable material. In some cases, the nominal gap is thinner at the layer than near the layer.

[0122] In some embodiments, each flux barrier comprises a conductive material that forms a loop around a core of core material that is more magnetically permeable than the conductive material. The core material may be ferromagnetic, and / or the core material and the magnetically permeable material of the passive pole may be adjacent portions of a laminated stack of plates.

[0123] In some cases, the loop forms part of the outer surface of the passive magnetic component that bounds the nominal gap.

[0124] In some cases, the core forms part of the outer surface of the passive magnetic component that is surrounded by the loop.

[0125] The loop bounds the nominal gap and may be positioned below the surface of the passive magnetic component, including the edges of the layers of the stack.

[0126] In some examples, the loop defines a capacitance, such as a capacitance formed at discrete locations along the loop. Preferably, the loop has a resonant frequency within the range of propagation of the magnetically permeable material of the passive pole.

[0127] In some embodiments, the passive magnetic component further includes flux barriers connecting adjacent passive poles of magnetically permeable pole material, the flux barriers each having a conductive material different from the pole material and defining at least one conductive path around the magnetically permeable core material. Preferably, the flux barriers are electrically isolated from each other outside the pole material, and adjacent flux barriers are positioned such that any conductive path defined in the conductive material of one flux barrier does not surround any portion of any conductive path defined in the conductive material of another flux barrier.

[0128] In some cases, each passive pole and / or each active pole has a plurality of teeth defining a recess therebetween.

[0129] In some examples, each active magnetic component has a flux shield extending along opposite edges of the active pole, the flux shield being formed of a material having a higher electrical conductivity than the material of the active magnetic component disposed between the flux shields.

[0130] In some applications, the ratio of maximum current to minimum current is at least 7: 1. In some examples, the ratio of maximum current to minimum current is at least 10:1.

[0131] Another aspect of the invention features a method of driving an electric motor, the method comprising: (a) energizing a first active pole of a series of active poles disposed along an air gap between the series of active poles and a passive magnetic component having a series of passive poles disposed along the air gap by pulsing a current through an electrical winding associated with the first active pole, the pulsing including a series of at least three pulses in which a winding of an adjacent active pole of the series of active poles is not energized; (b) pulsing a current through an electrical winding associated with a second active pole of the set of active poles, wherein the winding of the first active pole is de-energized; Passing current through the electrical winding associated with the second active pole according to a current waveform that includes a series of pulses, the current being energized by pulsing, and the ratio of maximum current to minimum current during pulsing of the current through the electrical winding associated with the second active pole being at least 4:1; Includes.

[0132] In some examples, energizing the first active pole includes pulsing the current at a pulse frequency between 2 Hz and 1 MHz, in some cases between 10 Hz and 20 kHz, and in some cases between 100 Hz and 5 kHz.

[0133] In some cases, energizing the first active pole and subsequently energizing the second active pole includes generating a first force between the first active pole and a passive pole across the air gap from the first active pole, and a second force between the second active pole and a passive pole across the air gap from the second active pole.

[0134] In some examples, the first and second forces induce relative motion between the active pole and the passive pole, which may include motion of the passive magnetic component relative to the active pole.

[0135] In some cases, the passive magnetic component is a rotor of a motor, and the relative motion comprises rotational motion of the rotor.

[0136] Some examples of this method include detecting rotor speed and controlling the frequency of the pulsed current in response to the detected rotor speed.

[0137] Some examples also include maintaining the current pulse frequency during rotor speed changes up to at least a rotor speed where the frequency at which each active pole is energized is at least one-half the pulse frequency.

[0138] In some cases, current is pulsed through the electrical windings associated with the first and second poles only at rotor speeds below that corresponding to one pulse per pole energization.

[0139] In some examples, the method includes, after energizing the second active pole, energizing a third active pole of the series of active poles located on an opposite side of the second active pole from the first active pole by pulsing current through an electrical winding associated with the third active pole, the pulsing including a series of at least three pulses in which the windings of the first and second active poles are not energized.

[0140] In some embodiments, the method further includes, after energizing the third active pole, re-energizing the first active pole by pulsing current through an electrical winding associated with the first active pole, and then re-energizing the second active pole by pulsing current through an electrical winding associated with the second active pole, and then re-energizing the third active pole.

[0141] In some examples, pulsing the current through the electrical winding associated with the first active pole passes a current through the electrical winding associated with the first active pole according to a current waveform in which the ratio of maximum current to minimum current during pulsing of the current through the electrical winding associated with the first active pole is at least 4:1, or in some cases at least 7:1.

[0142] In some examples, pulsing current through an electrical winding associated with the first active pole may include pulsing current through multiple coils conductively connected in parallel and wound around a common core. This includes converting it into a

[0143] In some cases, pulsing the current through the electrical winding associated with the first active pole includes operating a first switch between the voltage source and the electrical winding associated with the first active pole to open and close for a plurality of cycles.

[0144] In some embodiments, pulsing current through an electrical winding associated with the first active pole generates eddy currents in a first magnetic flux barrier adjacent to the passive pole across the air gap from the first active pole, the magnetic flux barrier having a higher conductivity than the passive pole across the air gap.

[0145] In some examples, the passive magnetic component further includes a second magnetic flux barrier, and the passive pole spanning the air gap from the first active pole is disposed between the first magnetic flux barrier and the second magnetic flux barrier, and the first magnetic flux barrier and the second magnetic flux barrier are electrically isolated from each other outside the passive pole.

[0146] In some cases, the passive pole is formed by a stack of layers of magnetically permeable material.

[0147] In some examples, eddy currents in the first flux barrier act to direct magnetic flux away from the first active pole.

[0148] In some configurations, a first magnetic flux barrier is positioned between a passive pole across the air gap from the first active pole and an adjacent passive pole, the magnetic flux barrier forming a loop of conductive material centered around a core of core material that has a higher magnetic permeability than the conductive material.

[0149] In some embodiments, the passive magnetic component further includes magnetic flux barriers between adjacent pairs of passive poles in the series of passive poles, each of the magnetic flux barriers including a conductive material different from the material forming the passive pole and defining at least one conductive path around the magnetically permeable core material.

[0150] In some cases, the flux barriers are electrically isolated from one another outside of a series of passive poles.

[0151] Adjacent magnetic flux barriers are preferably positioned such that any conductive path defined in the conductive material of one magnetic flux barrier does not enclose any portion of any conductive path defined in the conductive material of another magnetic flux barrier.

[0152] In some examples, the motor has a flux shield extending along both edges of each active pole, the flux shield being formed of a material having a higher electrical conductivity than the material of the active magnetic components disposed between the flux shields. In some cases, the flux shield extends into the gap between adjacent electrical windings. For example, the flux shield may extend from the air gap to a magnetically permeable yoke connecting adjacent active poles.

[0153] In some cases, the ratio of maximum current to minimum current is at least 7:1 or at least 10:1.

[0154] Some aspects of the present invention feature flux barriers for improving the performance of electric motors (e.g., increasing torque and power density). The flux barriers have dynamic (or temporary) diamagnetic properties. By utilizing flux barriers in motors, significant gains in torque can be achieved by directing the magnetic flux in a near-tangential direction. Here, the magnetic field is altered by redirecting the radial (or normal) forces along the tangential direction. That is, the average force vector during operation is near-tangential. Whereas, the dominant force vector in conventional motor designs is radial in nature.

[0155] The permeability of the flux barrier can be controlled by adjusting the magnetic frequency of the eddy currents in the flux barrier (e.g., by pulsing the current through the electrical winding of the active pole). In this way, the electric motor can have significantly different magnetic properties at various magnetic frequencies. At low frequencies, the flux barrier is ferromagnetic in nature, and at intermediate to high operating frequencies, the permeability of the flux barrier can be less than that of air, and the flux barrier is diamagnetic in nature.

[0156] The present invention may also create a high-reactance circuit in which the magnetic field is substantially reflected rather than propagating through the electromagnetic cycle. This may reduce or eliminate magnetic flux fringing. Unlike conventional permanent magnet (PM) motors, nearly zero magnetic flux propagates within the flux barriers in motors designed according to the present invention, avoiding demagnetization (coercivity) and excessive heat during operation. Furthermore, diamagnetic flux barriers behave differently from PM motors because they do not generate a magnetic field during operation and therefore are completely free of a magnetic field (not a magnetic field that exists in an opposing direction and then closes).

[0157] The present invention can be applied to various types of motors to improve their performance. The motor can be a radial gap motor, an axial gap motor, or a linear motor. For example, the motor can be a switched reluctance motor (SRM), an induction motor (IM), or a permanent magnet motor (PM).

[0158] Various examples of the invention disclosed herein can provide exceptionally high motor performance with significant torque / force and power density, and can be used to provide inherently smooth and efficient output shaft power for propelling vehicles as well as in stationary systems. These design concepts can more efficiently increase torque and power by increasing the saliency ratio of the motor itself, avoiding some of the traditional trade-offs that benefit one at the expense of the other. The motor can also achieve higher system efficiency during cycling due to the avoidance of magnetic breakdown that can occur with permanent magnet motors under passive conditions.

[0159] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the following specification. Other features, objects, and advantages of the invention will be apparent from the specification and drawings, and from the claims. [Brief explanation of the drawings]

[0160] DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 is a schematic diagram of an example electric drive system. [Figure 2]FIG. 1 is a schematic diagram of a motor controller including power switching. [Figure 2A] FIG. 2 is a schematic diagram of an exemplary power switch for an electrical winding. [Figure 3] 1 shows the current profile of the pole energization duty cycles including the pulsed current within each duty cycle. [Figure 4] 1 shows a radial gap motor including a rotor and a stator. [Figure 5] FIG. 5 is an enlarged view of a portion of FIG. [Figure 6] FIG. 1 is a perspective view of a rotor made from a stack of laminated plates. [Figure 7] 1 shows a rotor with flux barriers filled in the slots between adjacent poles. [Figure 8A] The magnetic flux due to the air between the poles at the misaligned position is shown. [Figure 8B] The magnetic flux due to the air between the poles at the 1 / 2 alignment position is shown. [Figure 8C] The magnetic flux due to the air between the poles in the aligned position is shown. [Figure 9A] 1 shows the magnetic flux due to the flux barrier between the poles in the misaligned position. [Figure 9B] The magnetic flux due to the magnetic flux barrier between the poles at the half alignment position is shown. [Figure 9C] 1 shows the magnetic flux due to the flux barrier between the poles in the aligned position. [Figure 10] The forces are shown with and without a flux barrier between adjacent poles. [Figure 11] FIG. 10 is a perspective view of another rotor having a flux barrier including a conductive layer over a magnetically permeable material in slots between adjacent poles. [Figure 12] 12 shows the magnetic flux between the stator and rotor of FIG. 11 during operation. [Figure 13] FIG. 10 is a perspective view of another rotor having flux barriers created by alternating conductive and magnetically permeable layers in the slots between adjacent poles. [Figure 13A] 14 shows the magnetic flux paths within the rotor of FIG. [Figure 14] FIG. 10 is a perspective view of another rotor having flux barriers made of a conductive layer surrounding magnetically permeable material in slots between adjacent poles. [Figure 15] FIG. 1 is a perspective view of an alternative rotor having flux barriers made of conductive loops centered on a magnetically permeable core between adjacent poles ("shield poles"). [Figure 15A] FIG. 16 is a side view of the rotor of FIG. 15. [Figure 16] FIG. 10 is a schematic diagram of an alternative rotor having flux barriers made of shield poles each with a discrete capacitor. [Figure 17] FIG. 10 is a perspective view of another rotor having flux barriers made of conductive layers cast onto the outer surface of a magnetically permeable material between each adjacent pole. [Figure 18] FIG. 10 is a perspective view of another rotor having flux barriers made of conductive layers formed on the outer surface of a magnetically permeable material between each adjacent pole. [Figure 19] 19 shows a motor including the stator and rotor of FIG. 18. [Figure 20] 1 shows the effect of magnetic frequency on the generated force for various magnetic flux barrier materials. [Figure 21] FIG. 10 is a perspective view of another rotor having flux barriers including conductive bands extending longitudinally along the rotor and conductively connected by a top conductive layer. [Figure 22] 22 shows the rotor of FIG. 21 without the flux barriers. [Figure 23] 22 shows the flux barriers in the rotor of FIG. [Figure 24] FIG. 10 is a perspective view of another rotor having distributed flux barriers inside the rotor. [Figure 25] FIG. 25 is a perspective view of the rotor of FIG. 24 without the flux barriers. [Figure 26] FIG. 25 is a perspective view of a flux barrier having multiple distributed portions within the rotor of FIG. 24. [Figure 26A] 27 shows the dispersed portion of the flux barrier of FIG. [Figure 27] 1 shows multiple discrete teeth on each pole of a motor with flux barriers in the slots of adjacent rotor poles. [Figure 28]FIG. 1 is a perspective view of an axial gap motor having flux barriers in the slots of the rotor poles. [Figure 29] 1 shows a rotor in an axial gap motor with shield poles as flux barriers between adjacent poles. [Figure 30] FIG. 30 is an open view of the rotor with shield poles of FIG. 29. [Figure 31] FIG. 30 is an open view of the rotor with shield poles of FIG. 29. [Figure 32] FIG. 30 is an open view of the rotor with shield poles of FIG. 29. [Figure 33] FIG. 1 is a perspective view of a stator having flux barriers that include conductive material extending into the edges of the stator poles and filled into the slots between adjacent stator poles. [Figure 34] FIG. 34 is a schematic diagram of the stator of FIG. 33 relative to the rotor. [Figure 35] FIG. 10 is a perspective view of another stator having flux barriers including conductive material formed on the edges of the stator poles and filled in the slots between adjacent stator poles. [Figure 36] FIG. 36 is a schematic diagram of the stator of FIG. 35 relative to the rotor. [Figure 37] FIG. 10 is a perspective view of another stator having flux barriers including conductive material fitted within slots between adjacent stator poles and aligned to the edges of the stator poles. [Figure 38] FIG. 38 is a schematic diagram of the stator of FIG. 37. [Figure 39] FIG. 1 is a perspective view of an exemplary linear motor including a rotor with flux barriers between rotor poles. [Figure 40] FIG. 40 is a schematic diagram of the linear motor of FIG. 39. [Figure 41] FIG. 1 is a perspective view of another example linear motor including multi-tooth stator poles and flux barriers filled into the rotor poles. [Figure 42] FIG. 42 is a schematic diagram of the linear motor of FIG. 41. DETAILED DESCRIPTION OF THE INVENTION

[0161] Like reference symbols in the various drawings indicate like elements.

[0162] Detailed Description Embodiments of the present disclosure provide systems, devices, and methods for using magnetic flux barriers to increase the performance of electric motors. Various designs / configurations of motor magnetic flux barriers are presented and discussed. The magnetic flux barriers are configured to exhibit diamagnetic properties at operating frequencies so that magnetic flux passing through a magnetic gap between an active magnetic component (e.g., a stator) and a passive magnetic component (e.g., a rotor) is concentrated and redirected in a near-tangential direction, thereby increasing torque.

[0163] Exemplary Electric Drive System 1 shows an electric drive system 100 including an electric motor 102 and a motor controller 104 coupled to the electric motor 102. The motor controller 104 is configured to operate the electric motor 102 to drive a load 110. The load 110 may be an additional gear train, such as a planetary gear set or another motor, in which multiple motors may be linked and operated in parallel.

[0164] The electric motor 102 has an output shaft 107 (considered to be the reference for rotation and other motion of the motor components) that is rotatable relative to a motor housing 105. In use, the output shaft 107 may be coupled to a load 110 that can provide rotational power when the motor 102 is electrically activated by appropriate power and signals from a motor controller 104. The output shaft 107 may extend through the motor and be exposed at both ends, meaning that rotational power can be transmitted at both ends of the motor. The housing 105 may be rotationally symmetric about the axis of rotation of the output shaft, but may be of any outer shape and will typically include means for securing the housing to another structure to prevent housing rotation during motor operation.

[0165] The electric motor 102 includes an active magnetic component 106, such as a stator, and a passive magnetic component 108, such as a rotor. For purposes of illustration, the stator will be used hereinafter as a representative example of the active magnetic component, and the rotor will be used hereinafter as a representative example of the passive magnetic component.

[0166] The rotor 108 is associated with the stator 106 and may be disposed within the stator 106, for example, in an internal rotor radial gap motor, or parallel to the stator, for example, in an axial gap motor. As explained in more detail below, properly controlled electrical activity within the stator 106 drives motion of the rotor 108. The rotor 108 is rotatably coupled to the output shaft 107 such that any rotational component of the resulting rotor motion is transmitted to and rotates the output shaft 107. The stator 106 is fixed to the motor 102 so that the rotor 108 moves about or parallel to the stator 106 during operation.

[0167] The stator 106 defines a plurality of stator poles with associated electrical windings, as shown in further detail in FIG. 4 , and the rotor 108 includes a plurality of rotor poles. As shown with further detail in FIG. 5 below, the rotor 108 defines a nominal air gap between the stator poles and the rotor poles. The rotor 108 is movable relative to the stator 106 along the direction of motion. As shown in FIG. 2 , the stator 106 has a plurality of independently energizable windings 132 spaced circumferentially about the rotor 108. Multiple adjacent windings 132 of the stator 106 are simultaneously energizable as a winding set, and the stator 106 may include a plurality of such multiple winding sets spaced about the stator 106. The motor 102 may also include a winding controller 130 having a set of switches 134 operable to activate the windings 132 of the stator 106. The switches 134 may be semiconductor switches (e.g., transistors such as metal oxide semiconductor field effect transistors (MOSFETs)). The winding controller 130 is coupled to the gates of the switches 134 and controls the respective control voltages. The winding controller 130 may be operable to transmit a control voltage to each switch 134. The control voltage may be a direct current (DC) voltage. The winding controller 130 may reside within the motor controller 104.

[0168] While only three switches are shown in FIG. 2 , it will be understood that the motor controller 104 may have a switch per stator pole or multiple switches for energizing multiple coils. Adjacent pole pairs may be wired in series through a common switch; in such cases, the instantaneous high speed of the two moving rotors may generate a slightly larger back electromotive force (EMF) compared to the slower pole and instantaneously draw more relative power, thereby providing additional acceleration and relative speed decoupling. Higher frequency excitation may reduce the effects of low-frequency harmonic ripple during operation. Switches 134 may be wired in parallel to balance the relative speeds between multiple rotors in a nested configuration by using parallel inductive load reactors. In some embodiments with a nested rotor configuration, individual rotors in the system may be driven individually, and any harmonic frequencies may be bypassed from one rotor to another by reducing the load on a given rotor. In some other embodiments, the rotors may be nested in pairs to locally balance the forces between the inner and outer rings.

[0169] FIG. 2A shows another exemplary power switch 200 for an individual electrical winding 132. The power switch 200 may have an H-bridge circuit including four switching elements 202a, 202b, 202c, and 202d arranged in an H-shaped configuration with the electrical winding 132 at its center. The switching elements 202a, 202b, 202c, and 202d may be bipolar or FET transistors. Each switching element 202a, 202b, 202c, and 202d may be coupled to a respective diode D1, D2, D3, and D4. The diodes are called catch diodes and may be of the Schottky type. The top end of the bridge is connected to a power supply (e.g., a battery Vbat) and the bottom end is connected to ground. The gates of the switching elements may be coupled to the winding controller 130, which is operable to send a respective control voltage signal to each switching element. The control voltage signal may be a DC voltage signal or an AC (alternating current) voltage signal.

[0170] The switching elements may be individually controlled by the controller 130 and may be turned on / off independently. In some cases, when switching elements 202a, 202d are turned on, the left lead of the stator is connected to a power source and the right lead is connected to ground. Current begins to flow through the stator, energizing the electrical winding 132 in a forward direction. In some cases, when switching elements 202b, 202c are turned on, the right lead of the stator is connected to a power source and the left lead is connected to ground. Current begins to flow through the stator, energizing the electrical winding 132 in a reverse direction. That is, by controlling the switching elements, the electrical winding 132 may be energized / activated in either of two directions.

[0171] The motor controller 104 (e.g., winding controller 130) may be configured to sequentially operate switches 134 or 200 for each pole energization duty cycle to generate magnetic flux across the air gap between the stator poles and the rotor poles, as described in further detail in FIGS. 8A-8C. The switches may be controlled to sequentially energize the stator poles to generate a local attractive force that pulls on the rotor. Such sequential energization (or activation) may cause rotation of the rotor 108, output shaft 107, and load 110.

[0172] As discussed in more detail below, various types and configurations of flux barriers may be implemented within rotor 108 and / or stator 106. Flux barriers typically have diamagnetic properties greater than air during operation.

[0173] In some examples, the flux barriers are made of aluminum, copper, brass, silver, zinc, gold, pyrolytic graphite, The flux barriers are made of a single material, such as graphite, bismuth, graphene, or carbon nanotubes. In some examples, ferromagnetic composite materials, such as copper-iron, nickel-iron, lead-iron, brass-iron, silver-iron, zinc-iron, gold-iron, bismuth-iron, aluminum-iron, pyrolytic graphite-iron, graphene-iron, carbon nanotube-iron, or Alinco (aluminum-nickel-cobalt) alloy, can be used as flux barriers, often with higher electrical conductivity than the ferromagnetic material (e.g., iron) that makes up the rotor poles. In some cases, the flux barriers (e.g., made of copper-iron) have a lower effective permeability than the ferromagnetic material. In some cases, the flux barriers (e.g., made of nickel-iron) have a higher effective permeability than the ferromagnetic material. In some examples, the flux barriers are constructed as shielding poles of conductive material that form loops around a core of core material that has a higher magnetic permeability than the conductive material. Due to the conductive material of the loop, the shielding poles can also have a higher effective conductivity than the core material (which can be iron, for example).

[0174] Another material property of interest (called the EMF shielding factor) is the quotient of electrical conductivity and magnetic permeability (e.g., siemens / henry). The EMF shielding factors of two materials can be determined simultaneously by placing equal-sized samples of the materials on a nonconducting support so that their principal planes of conduction (e.g., the orientation of the planes as experienced during operation in a magnetic system) are perpendicular to the magnetic field generated during Helmholtz coil excitation, and then moving the samples between two parallel Helmholtz coils with larger diameters than the samples. For a given excitation waveform (e.g., voltage, shape, frequency), the current in the Helmholtz coils will be proportional to the EMF shielding factor of the material between the coils, such that an increase in the EMF shielding factor is observed as an increase in current during constant excitation.

[0175] As noted above and discussed in more detail below, the flux barriers are configured to be diamagnetic. The permeability of the flux barriers can be controlled by adjusting the magnetic frequency through the flux barriers. In this way, the motor can have significantly different magnetic properties at various magnetic frequencies. At low frequencies, the flux barriers can have a permeability at or near that of a ferromagnetic material, and at intermediate to high operating frequencies, the permeability of the flux barriers is preferably less than that of air, and the properties of the flux barriers are diamagnetic.

[0176] As shown in more detail in Figures 9A-9C, implementing diamagnetic materials or structures within the rotor and / or stator can provide a means of improving magnetic flux concentration during motor operation. Specifically, when the stator and rotor poles are completely misaligned, significant internal electromagnetic reflections (due to the diamagnetic properties of the flux barrier) significantly inhibit magnetic transmission through the flux barrier. The flux shielding can be significantly greater if the flux barrier is replaced with air slots between adjacent poles, as in some conventional motors. This diamagnetic shielding effectively causes the flux barrier to push against the rotor, while the magnetic pole reluctance pulls against the rotor. This effect allows more energy to be generated from the motor system per cycle.

[0177] To operate the diamagnetic flux barrier at the operating frequency, as shown in FIG. 3, during each active pole's pole energization (pole energization) duty cycle, the motor controller 104 is configured to pulse the current through the pole's winding at a pulse frequency. Unlike an induction motor, which pulses each pole in turn once at a slow speed, the motor controller 104 pulses the current through a single pole multiple times at a slow speed. These multiple pulses to the same pole before pulsing a subsequent pole constitute one energization duty cycle. In some examples, the motor controller pulses the current through the active pole's winding during a pole energization duty cycle that includes a series of at least three pulses. During this series, the winding of an adjacent active pole is not energized. The electrical circuit including each pole's electrical winding is configured so that the ratio of maximum to minimum current through the energized pole's winding during current pulsing is at least 4:1, in some cases at least 7:1, or in some cases even 10:1. The minimum current through the winding between pulses is It can be as low as zero.

[0178] The pulse current causes an alternating magnetic strength (e.g., magnetic field) that induces eddy currents in the diamagnetic flux barrier. For a given flux barrier material, the higher the pulse frequency, the greater the eddy currents. The induced eddy currents generate a secondary magnetic field that opposes the applied alternating magnetic field, thereby generating a repulsive force. As shown in more detail in Figures 9A-9C and 10, the repulsive force can concentrate and redirect the magnetic flux approximately tangentially along the direction of relative motion between the rotor and stator, thus increasing the force available to do work. Additionally, flux barriers of different materials or designs can have different diamagnetic properties. The higher the diamagnetic properties of the flux barrier, the greater the eddy currents induced at a given magnetic (pulse) frequency. Therefore, the horizontal force generated is a function of the magnetic frequency and the structure of the flux barrier, as discussed in more detail below with reference to Figure 20.

[0179] The magnetic frequency of the diamagnetic flux barrier (and the horizontal force generated) is determined by the pulse frequency of the current through the pole winding during each active pole's energization duty cycle. The pulse frequency is, for example, in some cases 2 Hz to 1 MHz, in some cases 10 Hz to 20 kHz, and in some cases 100 Hz to 5 kHz. In some cases, the motor controller is configured to maintain the pulse frequency during motor speed changes, at least up to a motor speed where the energization duty cycle frequency per active pole is at least one-half the pulse frequency. In some cases, the motor controller is configured to pulse the current only below a motor speed corresponding to one pulse per energization duty cycle. In some implementations, at least one of the electrical windings includes multiple coils conductively connected in parallel and wound around a common core. Such electrical windings may have a low reactance, allowing for faster decay of the current between pulses.

[0180] Exemplary Motor Figure 4 shows an example motor 400 including a stator 410 and a rotor 420. Motor 400, stator 410, and rotor 420 may be electric motor 102, stator 106, and rotor 108, respectively, of Figure 1. Motor 400 is a radial gap motor, such as a switched reluctance motor (SRM), with rotor 420 disposed within stator 410. Figure 5 is an expanded view of a portion of Figure 4.

[0181] The stator 410 features a series of circumferentially spaced stator poles 412, each including a stator core 414 and associated electrical windings 416 surrounding the stator core 414. The stator 410 may have, for example, multiple stator projections that protrude from a stator back plate 402 (e.g., a yoke or back iron) to create stator slots 418 and stator core 414. The slots 418 exist between adjacent stator poles 412. The stator core 414 may be of one continuous piece or a combination of individual components assembled into the motor. A continuous piece provides greater dimensional integrity with zero air allowed within the stator assembly, while a series of discrete stator poles maintained in mechanical alignment by a stator housing may allow for efficient manufacturing and assembly. The terminal ends of the stator projections may be distributed, linear, or subordinate to the stator projections and back iron or yoke. In this example, the stator projections are straight and of constant cross section from the yoke to their far ends in the air gap 430 defined between the stator 410 and rotor 420, as shown in FIG.

[0182] The stator poles 412 allow electromagnetic communication between the power electronics and the stator core 414 and have electrical insulation between the pole windings. The electrical windings 416 may include a conductive coil of wire, such as insulated or enameled magnet wire, or multiple welded conductive bands, such as insulated copper bands. The electrical windings 416 may include windings of braided wire, such as Litz wire. Litz wire is , may be used for high frequency operation, and other configurations such as rectangular or flat wire may be used to increase winding density and increase skin effect. Each electrical winding 416 may include multiple coils conductively connected in parallel and wound around a common stator core 414.

[0183] The rotor 420 also has a series of circumferentially spaced rotor poles 422 that define slots 423 therebetween. The rotor 420 has a surface 402 that is movable relative to a surface 401 of the stator 410 in the direction of motion. The slots 423 extend at a non-zero angle (e.g., 90 degrees) relative to the direction of motion. The surface 402 of the rotor 420 is spaced from the surface 401 of the stator 410 to define an air gap 430 between the stator poles 412 and 422. It should be noted that the air gap 430 may be filled with another fluid other than air.

[0184] The air gap 430 can be consistently maintained during operation. In the motor described below, the stator poles 412 and rotor poles 422 should maintain a non-zero air gap to prevent catastrophic damage resulting from contact of the rotor poles 422 with the stator poles 412. As shown in FIG. 5 , the air gap 430 has a depth Dg perpendicular to the direction of motion. The depth Dg can range from 0.05 to 2.0 millimeters (e.g., for motors with an output of less than 250 kilowatts (kW)). The rotor poles 422 can have a width Wl along the direction of motion, and the rotor slots 423 can have a width W2 along the direction of motion and a depth Ds perpendicular to the direction of motion. As discussed in more detail below, the dimensions of the air gap 430 can affect the horizontal force generated. In some examples, slot 423 has a preferred depth Ds of 50-500 times the depth (Dg) of air gap 430 and a preferred width W2 at surface 402 of 25-100 times the depth Dg of air gap 430. As discussed in further detail below, flux barriers may be disposed within slots 423 between rotor poles 422 and / or within slots 418 between stator poles 412, which may alter the magnetic flux flow between stator 410 and rotor 420 and modify the performance of motor 400. In this example, the flux barriers fill the slots. The dimensions of air gap 430 and slot 423 may affect the performance of motor 400.

[0185] FIG. 6 is a perspective view of an example stator core 600 made of a stack of laminations 601 of ferromagnetic material. The rotor core 600 can be used for the rotor 420 of FIG. 4. The laminations 601 are separated from one another at least at the surface of the rotor 600 by interfaces 603 that are less conductive than the ferromagnetic material. Thus, the interfaces are current-restricting compared to the ferromagnetic material of the laminations. In some cases, the interfaces 603 comprise an oxidized surface of the ferromagnetic material. For example, the ferromagnetic material can be iron (Fe) and the interfaces can be made of iron oxide (FeOx). In some cases, the interfaces 603 include sheets of insulating material interleaved with the ferromagnetic layers 601. For example, the sheets of insulating material can include sheets of resin film.

[0186] The laminations 601 define a rotor body 606 having an axial bore 605 into which an output shaft (e.g., output shaft 107 of FIG. 1 ) may be inserted and which may be movable with the rotor core 600. The laminations 601 also define a series of spaced apart rotor poles 602 that project radially from the rotor body 606 and extend axially parallel to the axial bore 605. The projecting rotor poles 602 define axially extending slots 604 parallel to the axial bore 605.

[0187] Exemplary Magnetic Flux Barriers Below, various designs / configurations of flux barriers for electric motors including SRMs, axial gap motors and linear motors are presented and discussed.

[0188] Exemplary magnetic flux barrier with conduction bands 7 shows an example rotor 700 in which magnetic flux barriers fill the slots between adjacent rotor poles. Rotor 700 may include rotor core 600 of FIG. 6, and rotor poles 702 may be rotor poles 602 of FIG. 6. Rotor poles 702 are separated by interfaces that are less conductive than the ferromagnetic material. The magnetic layer may be a stack of layers of ferromagnetic material separated from each other by a magnetic field.

[0189] Adjacent rotor poles 702 define slots (e.g., slots 604 in FIG. 6 ). Rotor 700 includes magnetic flux barriers 704 between adjacent rotor poles 702 and within the slots of adjacent rotor poles 702. The magnetic flux barriers 704 each have a higher electrical conductivity than the ferromagnetic material. The magnetic flux barriers 704 are electrically isolated from each other outside the ferromagnetic material of rotor 700, but may be electrically connected to each other through the rotor material.

[0190] 7, the magnetic flux barriers 704 may be in the form of conductive bands that extend axially along the rotor 700 (e.g., parallel to the axial bore 605 in FIG. 6) and intersect multiple interfaces of the layer stack. In some examples, the conductive bands are formed of a single material, such as aluminum, copper, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, or carbon nanotubes. In some examples, the conductive bands include composite materials, such as copper-iron, nickel-iron, lead-iron, brass-iron, silver-iron, zinc-iron, gold-iron, bismuth-iron, aluminum-iron, pyrolytic graphite-iron, graphene-iron, carbon nanotube-iron, or Alinco (aluminum-nickel-cobalt) alloy, such that the conductive bands (e.g., copper-iron) may have a higher conductivity than the ferromagnetic material of the rotor core. In some cases, the conductive bands include at least 1%, in some cases 5%, and in some cases 15% by mass of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes. In some cases, the conductive bands include at least 20%, in some cases 40%, and in some cases 60% by mass of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt. Rotor 700 can be fabricated by directly casting one or more materials of flux barriers 704 into the slots between rotor poles 702 such that the slots are filled with the flux barriers.

[0191] A rotor 700 having magnetic flux barriers 704 in slots between rotor poles 702 can be used as the rotor 420 of FIG. 4 in a motor (e.g., motor 400 of FIG. 4). The rotor 700, together with a stator (e.g., stator 410 of FIG. 4), defines a nominal gap between the stator poles and the rotor poles (e.g., gap 630 of FIG. 6). The conductive bands have exposed surfaces facing the nominal gap. Often, the exposed surfaces of the conductive bands form a cylindrical surface with the surfaces of the rotor poles.

[0192] The effect of magnetic flux barriers 8A-C and 9A-C show the effect of flux barriers on the magnetic flux between the stator and rotor poles and through the nominal gap. Figures 8A-C show the magnetic flux with no flux barriers (e.g., air filling the slots) between the rotor poles in a fully misaligned position (Figure 8A), a half-aligned position (Figure 8B), and a fully aligned position (Figure 8C).

[0193] When a stator pole 802 (e.g., stator pole 412 in FIG. 4) is energized, a magnetic field is generated and magnetic flux flows between the stator pole 802 and a rotor pole 804 (e.g., rotor pole 422 in FIG. 4 or rotor pole 602 in FIG. 6). The rotor pole 804 is movable relative to the stator pole 802 in a direction of motion parallel to a nominal gap 805 defined between the rotor pole 804 and the stator pole 802.

[0194] In the fully misaligned position, as shown in FIG. 8A, magnetic flux 810 flows at an angle to the direction of motion. Some of the magnetic flux 810 flows through air-filled slot 803 adjacent to stator pole 802 to rotor pole 804, and some of the magnetic flux 810 flows through air-filled slot 806 adjacent to rotor pole 804 to rotor pole 804. In the half-aligned position, as shown in FIG. 8B, more of the magnetic flux 820 flows through nominal gap 805 and less through stator slot 803 and rotor slot 806. The angle between magnetic flux 820 and the direction of motion is larger. In the aligned position, as shown in FIG. As shown at C, magnetic flux 830 flows approximately radially through the nominal gap 805 to the rotor poles 804. The angle between the magnetic flux 830 and the direction of motion is approximately 90 degrees.

[0195] 9A-C show the same three relative rotor-stator positions, but with flux barriers filling the slots between adjacent rotor poles 904, and the rotor poles in a fully misaligned position (FIG. 9A), a half-aligned position (FIG. 9B), and a fully aligned position (FIG. 9C). When a stator pole 902 is energized, a magnetic field is generated and magnetic flux flows from the stator pole 902 to the rotor pole 904, with the rotor pole 904 and stator pole 902 defining a nominal gap 905.

[0196] In the misaligned position, as shown in FIG. 9A , magnetic flux 910 flows at an angle to the direction of motion. A portion of the magnetic flux 910 flows to the rotor pole 904 through a slot 903 adjacent to the stator pole 902, and a portion of the magnetic flux 910 flows to the rotor pole 904 through a flux barrier 906 filled in a slot adjacent to the rotor pole 904. However, compared to the magnetic flux 810 in FIG. 8A , the portion of the magnetic flux through the flux barrier 906 is more constrained and deflected because the magnetic flux 810 is concentrated and extends more along the nominal gap 905, such that it is redirected more tangentially along the direction of motion. Similarly, in the half-aligned position, as shown in FIG. 9B , magnetic flux 920 is more concentrated compared to the magnetic flux 820 in FIG. 8B , and in particular, the portion of the magnetic flux through the flux barrier 906 is more constrained and repelled. In the aligned position, as shown in FIG. 9C, magnetic flux 930 is similar to magnetic flux 830 and flows substantially through nominal gap 905 to rotor pole 904.

[0197] At operating magnetic frequencies, the flux barriers exhibit diamagnetic properties to repel magnetic flux, thereby generating a repulsive force against the rotor poles. When the stator and rotor poles are misaligned, significant internal electromagnetic reflections at the flux barriers change the net direction of magnetic flux between the poles. The shielding diamagnetic material in slots filled by the flux barriers effectively pushes the rotor in the desired direction of motion, while the magnetic attractive force between the stator and rotor poles pulls the rotor in the same direction. Thus, by using such diamagnetic barriers, the vectors of the magnetic field lines can be modified during motor operation so that the radial force is directed approximately along the direction of motion. This increases the proportion of magnetic induction forces that propel the rotor relative to the stator. This effect generates more useful kinetic energy per cycle from a given input energy from an electric drive system (e.g., electric drive system 100 of FIG. 1). For example, as the rotor poles travel from a fully misaligned position to a fully aligned position relative to the stator poles, the difference in co-energy of a slot with a flux barrier is much larger than the difference in co-energy of a slot without a flux barrier such as air, which can also better avoid fringing fields. In other words, the effective saliency ratio is increased.

[0198] 10 illustrates the net magnetic induction force with and without a magnetic flux barrier between adjacent poles. When a stator pole 1012 of a stator 1010 (e.g., stator pole 412 of FIG. 4) is energized, a magnetic field is generated and magnetic flux flows from the stator pole 1012 to a rotor pole 1022 of a rotor 1020 (e.g., rotor pole 422 of FIG. 4 or rotor pole 602 of FIG. 6). The rotor 1020 is movable relative to the stator 1010 in the direction of motion and defines a nominal gap 1015 with the stator 1010.

[0199] When only air is present in the slots 1024 between adjacent rotor poles 1022, the attractive forces between the stator poles 1012 and the rotor poles 1022 cause a net instantaneous attractive force F at an angle θ relative to the direction of motion. When a magnetic flux barrier 906 is present in the slots 1024 between adjacent rotor poles 1022 and / or in the slots 1014 between adjacent stator poles 1012, the attractive forces between the stator poles 1012 and the rotor poles 1022 cause a net attractive force F at an angle θ relative to the direction of motion. As discussed above in FIGS. 9A and 9B, the magnetic flux barriers may exhibit diamagnetic properties to repel magnetic flux, effectively creating a repulsive force against the stator poles. This As a result, the net attractive force F1 is redirected to have a larger component along the direction of motion. That is, F1 cos θ1 > F0 cos θ2, where F1 may be approximately equal to F0. When the rotor poles 1022 are in a fully misaligned position, as shown in FIG. 9A, the angle is minimum and the horizontal force is maximum. When the rotor poles 1022 are in a half-aligned position, as shown in FIG. 9B, there is a maximum change in reluctance and maximum torque can be obtained.

[0200] Exemplary magnetic flux barrier with conductive layer on strips FIG. 11 is a perspective view of another rotor 1100 having magnetic flux barriers 1104 in slots between adjacent rotor poles 1102. Similar to the rotor 700 of FIG. 7, the rotor poles 1102 are made of a stack of layers of ferromagnetic material separated from each other by interfaces that are less conductive than the ferromagnetic material. The interfaces may be current-restricting. The magnetic flux barriers 1104 include conductive bands 1108 that each intersect multiple interfaces and are electrically isolated from each other outside the ferromagnetic material. Unlike the magnetic flux barriers 704 of the rotor 700 of FIG. 7, the magnetic flux barriers 1104 of the rotor 1100 additionally include a conductive layer 1106 that covers the bands 1108. The conductive layer 1106 is made of a different material than the conductive bands 1108 and may have a higher conductivity than the conductive bands 1108. In some examples, the bands 1108 are made of iron, nickel, or cobalt, and the conductive layers 1106 are made of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, or carbon nanotubes. The rotor 1100 can be fabricated by casting the material of the conductive bands 1108 into the slots of the rotor poles 1102 and depositing the conductive layers 1106 onto the conductive bands 1108, such as by plating or sputtering.

[0201] The outer surface of the rotor 1100 and the outer surface of the stator 1120 define a nominal gap 1130, as shown in FIG. 12 . The rotor 1100 is movable relative to the stator 1120 in the direction of motion. A conductive layer 1106 at least partially forms the outer surface of the rotor 1100. During operation, when the stator poles 1122 of the stator 1120 are energized, for example, with a pulsed current having a duty cycle such as that shown in FIG. 3 , an alternating magnetic field is generated, and a corresponding magnetic flux 1202 flows from the stator poles 1122 through the nominal gap 1130 to the rotor poles 1102. The pulsed magnetic field induces eddy currents 1204 in the conductive layer 1106 of the magnetic flux barrier 1104. The eddy currents 1204, as discussed above, can generate a secondary magnetic field that opposes the applied alternating magnetic field, thereby generating a repulsive force to change the net direction of the magnetic flux 1202.

[0202] Conductive layer 1106 has a constant width W in the direction of motion and a constant thickness T from the outer surface of rotor 1100 along a direction perpendicular to the direction of motion (or nominal gap 1130), intersecting multiple interfaces of the layer stack. The width W of layer 1106 is preferably greater than two times, in some cases greater than five times, and in some cases greater than ten times the thickness T of layer 1106. Conductive band 1108 may be of a greater thickness than layer 1106.

[0203] In some examples, the thickness T of the layer 1106 is greater than the current skin depth of the material of the layer 1106 at a particular operating frequency, such that the eddy currents 1204 flow primarily in the skin of the layer 1106 between the outer surface and the skin depth, propagating long distances within the layer 1106 along the direction of motion toward adjacent rotor poles 1102. In this way, the magnetic flux 1202 can be more concentrated within the layer 1106 and can be redirected more tangentially to induce larger horizontal forces along the direction of motion.

[0204] Exemplary Flux Barrier with Alternating Layer Pairs 13 is a perspective view of another rotor 1300 having magnetic flux barriers 1304 in the slots between adjacent rotor poles 1302. Similar to rotor 1100 of FIG. 11, rotor poles 1302 may be made of a stack of layers of ferromagnetic material separated from each other by interfaces that are less electrically conductive than the ferromagnetic material. The magnetic flux barriers 1304 prevent the magnetic flux barriers from electrically connecting each other outside the ferromagnetic material of rotor 1300. 11 , each flux barrier 1304 of rotor 1300 is made of pairs of alternating layers 1306, 1308 disposed in the slots between adjacent rotor poles 1302. The discrete layers 1306, 1308 extend parallel to the nominal gap and form interlayer interfaces of various materials. In a specific example, layer 1306 is made of copper and layer 1308 is made of nickel. Layer 1306 may be more conductive than layer 1308, and layer 1308 may be more magnetically permeable than layer 1306. Rotor 1300 may be fabricated by alternately depositing layers 1306, 1308 in the slots between rotor poles 1302.

[0205] 13A, each layer 1306 has a constant thickness T1 in a direction perpendicular to the nominal gap, and each layer 1308 has a constant thickness T2 in a direction perpendicular to the nominal gap. In some examples, the thickness T1 of layer 1306 is configured to be less than the current skin depth of the material of layer 1306 at a particular operating frequency, and the thickness T2 of layer 1308 is configured to be less than the current skin depth of the material of layer 1308 at a particular operating frequency. In this manner, as shown in FIG. 13A, magnetic flux 1310 flowing from the stator to the rotor 1300 can propagate through the multiple layers 1306, 1308, generating eddy currents 1312 and therefore secondary magnetic fields within the multiple layers 1306, 1308.

[0206] Exemplary Flux Barrier with Shielding Poles FIG. 14 is a perspective view of another rotor 1400 having magnetic flux barriers 1404 in the slots between adjacent rotor poles 1402. Similar to the rotor 1100 of FIG. 11, the rotor poles 1402 are made of a laminated stack of layers of ferromagnetic material separated from each other by interfaces that are less conductive than the ferromagnetic material. The interfaces may be current-restricting. The magnetic flux barriers 1404 are electrically insulated from each other outside the ferromagnetic material. Unlike the magnetic flux barriers 1104 of the rotor 1100 of FIG. 11, which have a conductive layer on top of the strips, the magnetic flux barriers 1404 of the rotor 1400 have a layer 1406 of conductive material surrounding a core 1408 of core material in the slots between adjacent rotor poles 1402. The core material of the core 1408 may be more magnetically permeable than the conductive material of the layer 1406. The core 1408 may be of the same material as the rotor poles.

[0207] Layer 1406 includes three layer portions 1406a, 1406b, and 1406c. Layer portion 1406a covers the inter-pole surface area between adjacent rotor poles 1402 and forms a portion of the outer surface of rotor 1400. Each core 1408 underlies a respective inter-pole surface area. The inter-pole surface area may be continuous in a direction perpendicular to the direction of motion across the complete magnetically active extent of the pole surface area of ​​rotor 1400. Layer portions 1406b and 1406c extend from layer portion 1406a across the interface of the layer stack and between adjacent rotor poles 1402 and the flux barrier core 1408.

[0208] Similar to layer 1106 of FIG. 11 , each layer portion 1406a, 1406b, 1406c may have a thickness greater than the current skin depth of the conductive material of layer 1406 so that magnetic flux passing through layer portion 1406a is redirected more tangentially toward the adjacent rotor pole 1402, and layer portions 1406b, 1406c act to suppress or shield magnetic flux between the pole and core 1408. Layer portion 1406a has a constant width extending in the direction of motion. Layer portions 1406b, 1406c extend from the outer surface of rotor 1400 to their full depth into the ferromagnetic material. The full depth may be, for example, about 1-50 mm, in some cases about 2-25 mm, in some cases about 5-15 mm, and 2-2000%, in some cases 5-500%, or in some cases 10-200% of the width of layer portion 1406a.

[0209] The conductive material of the layers 1406 may include copper. In some embodiments, the core material of the core 1408 and the ferromagnetic material of the rotor poles 1402 have the same material properties (e.g., made of iron). The core 1408 and the rotor poles 1402 may be adjacent parts of a laminated stack of layers.

[0210] In some cases, rotor 1400 may be fabricated by depositing core material into slots between adjacent poles of a rotor (e.g., rotor 600 of FIG. 6 ) to form a core 1408 having gaps between the poles 1402 and adjacent cores 1408, and then depositing conductive material into the gaps and on top of core 1408 to form layer 1406. In some cases, layers of shaped ferromagnetic material are aligned and stacked to form slots to receive the conductive material, and then conductive material is cast or otherwise deposited into the gaps and over the top surface regions to form conductive layer 1406.

[0211] The magnetic flux barriers 1404 can be considered shield poles. Each shield pole can have the same dimensions as a rotor pole. At low frequencies or DC static conditions, there is little distinction between the rotor poles and the shield poles; however, under medium and high frequency operation, the reluctance of the shield poles exceeds the reluctance of air, resulting in higher torque density. Therefore, by forming shield poles between adjacent rotor poles, the vectors of the magnetic field lines of the reluctance poles (stator poles and rotor poles) during operation can be uniquely modified so that the magnetic field is nearly tangential. This allows the motor to utilize radial forces (or normal forces or radial pressures), which can be an order of magnitude larger than tangential forces, as tangential forces. The shield poles can also extend to adjacent stator pole pairs to further reduce the motor's flux fringing characteristics.

[0212] FIG. 15 is a perspective view of another rotor 1500 with another example of shield poles as magnetic flux barriers 1504 between adjacent rotor poles 1502. Each flux barrier 1504 is made of a conductive loop 1506 centered on a magnetically permeable core 1508 between adjacent poles 1502. The loop 1506 can be a stack of thin layers of conductive material (e.g., copper oxide, enamel, aluminum, or copper layers separated by aluminum oxide) of similar magnetic permeability but separated by less conductive material. Similar to the rotor 1400 of FIG. 14, the rotor poles 1502 can be made of a laminated stack of layers of ferromagnetic material separated from each other by interfaces that are less conductive than the ferromagnetic material. The magnetic flux barriers 1504 form inter-pole surface areas between the pole surface areas of the rotor poles 1502 and can therefore be considered surface shield poles. The inter-pole surface areas and the pole surface areas define the outer surface (or end face) of the rotor 1500. Each core 1508 forms a portion of the outer surface surrounded by a respective loop 1506. Each loop 1506 forms a portion of the cylindrical outer surface of the rotor 1500 as shown in Figure 15A.

[0213] The loops 1506 may be made of a conductive low-energy product. For example, the loops 1506 may be made of copper. The material of the core 1508 has a higher magnetic permeability than the material of the loops 1506. The core material may be a ferromagnetic material (e.g., iron). The core material of the core 1508 and the ferromagnetic material of the rotor poles 1502 may be the same, such as adjacent portions of a stack of layers. In some embodiments, the rotor 1500 is formed by etching areas of the ferromagnetic material of the stack of layers according to the shape and position of the loops 1506, and then depositing / casting a conductive material into the etched areas to form the loops 1506. Alternatively, the flux barrier may be formed of a conductive low-energy product disposed within the core 1508 itself.

[0214] The conductive loops 1506 of the flux barriers 1504 do not overlap and are electrically isolated from one another outside of the ferromagnetic material. The flux barriers 1504 are connected to one another only through the ferromagnetic material. The flux barriers 1504 define at least one conductive path (e.g., loop 1506) that is centered about the core material of the core 1508. "Non-overlapping" means that adjacent flux barriers 1504 are positioned such that any conductive path defined in the conductive material of one flux barrier does not enclose any portion of any conductive path defined in the conductive material of another flux barrier 1504.

[0215] As shown in FIG. 15, the loops 1506 of the flux barrier 1504 are made of a conductive material (e.g., copper). In some embodiments, the flux barriers may be formed by open loops of conductive material as shielding poles. For example, FIG. 16 is a schematic diagram of another rotor 1600 having flux barriers 1604 between adjacent rotor poles 1602. The flux barriers 1604 are similar to the flux barriers 1504 of FIG. 15, except that the flux barriers 1604 have open loops 1606 with breaks 1608 (e.g., air gaps) as shown in FIG. 16.

[0216] The open loop 1606 may also be made of a conductive material (e.g., copper). The open loop 1606 defines a capacitance that may be formed at discrete locations along the open loop 1606. For example, two opposing end faces of the open loop 1606 form an air gap 1608, forming a capacitor. The open loop 1606 may be configured to have a resonant frequency within the propagating range of the magnetically permeable material (e.g., iron) of the rotor poles 1602 of the rotor 1600. In some embodiments, the rotor 1600 is formed by etching an area of ​​magnetically permeable material according to the shape and location of the open loop 1606 and depositing / casting a conductive material into the etched area to obtain the loop 1606. The gaps 1608 may be formed during deposition of the conductive material or may be created by peeling or otherwise removing a strip of material to form each gap. Each capacitance gap 1608 preferably spans at least one layer interface of the stack.

[0217] Exemplary Magnetic Flux Barrier with Surface Layer FIG. 17 is a perspective view of another rotor 1700 having magnetic flux barriers 1704 between adjacent rotor poles 1702. Each magnetic flux barrier 1704 includes a conductive layer 1706 that forms the inter-pole surface area between the adjacent poles 1702. Similar to the rotor 1500 of FIG. 15, the rotor poles 1702 may be made of a laminated stack of layers of ferromagnetic material separated from each other by interfaces that are less conductive than the ferromagnetic material. However, unlike the magnetic flux barriers 1504 of FIG. 15 with conductive loops 1506, the conductive layer 1706 completely covers the inter-pole surface area and forms a portion of the outer surface of the rotor 1700. The conductive layer 1706 intersects substantially all of the magnetically active plates of the stack and preferably is in direct contact with each of the plates of the stack.

[0218] The conductive layer 1706 may be formed below the outer surface, for example, by etching the ferromagnetic material of the stack of layers to form the inter-pole regions and casting a conductive material into the inter-pole regions.

[0219] Figure 18 is a perspective view of another rotor 1800 having magnetic flux barriers 1804 between adjacent rotor poles 1802. Unlike the magnetic flux barriers 1704 of Figure 17, which have a conductive layer formed under the outer surface of the rotor 1700, each magnetic flux barrier 1804 includes a conductive layer 1806 formed on the outer cylindrical surface of the rotor 1800.

[0220] 19 , the conductive layer 1806 has a thickness that extends from its outer surface toward a nominal gap 1910 defined by the stator 1900 and the poles 1802 of the rotor 1800. The stator 1900 has an outer surface that defines a plurality of stator poles 1902 with associated electrical windings 1904. Because the conductive layer 1806 is formed on the cylindrical outer surface of the rotor 1800, it lies within the nominal gap 1910, causing the clearance between the rotor and the stator to be lower at the layer 1806 than near the layer 1806.

[0221] Effect of flux barrier material / configuration on force Figure 20 shows the force generated by motors with various flux barriers (e.g., various materials / configurations) under a range of frequencies. Here, force refers to the effective force parallel to the direction of motion in which the rotor is movable relative to the stator. Frequency refers to the magnetic frequency of the eddy currents induced in the flux barriers, which can be controlled by the pulse frequency of the current energizing the stator poles of the stator.

[0222] Curve 2002 represents air as a passive material filling the slots between adjacent rotor poles, where the effective force remains constant over low frequencies and eventually decays rapidly at high frequencies (e.g., above the core limit at point 2001). Curve 2004 represents a single filler material (e.g., copper) as a dynamic non-ferromagnetic flux barrier that behaves approximately like air at low frequencies but increases above the crossover frequency (at crossover point 2005). Curve 2006 represents a shield pole (e.g., loop pole) as a dynamic ferromagnetic flux barrier, where at lower frequencies (e.g., below the crossover frequency), the effective force is lower than that with air, while the effective force increases dramatically with frequency (e.g., above the crossover frequency) faster than that with the straight non-ferromagnetic material (e.g., copper) filler represented by curve 2004. Along curve 2006, point 2003 indicates the reluctance lower force limit of the conductive slot, point 2005 indicates the crossover frequency, and point 2007 indicates the air gap limited peak force.

[0223] To avoid the drop in force at low speeds, the motor can be operated at a high magnetic frequency, for example, by pulsing the current through each pole winding at a low revolutions per minute (RPM), thereby increasing the output force. The reason the force of the shield pole is lower than that of air at low frequencies can be largely attributed to the presence of alternating ferromagnetic flux paths, which result in a relative reluctance asymmetry. At high frequencies, the motor is dominated by the relative inductive shielding that occurs at crossover frequencies. This is the point 2005 where the saliency ratio of the shield pole is equal to that of air (effectively, the skin depth of the shield pole closely resembles that of air). As frequency increases, the saliency ratio of the shield pole continues to increase.

[0224] Curve 2012 represents a non-ferromagnetic superconductor as a straight-fill material flux barrier, where a greater force gain than air is induced even at relatively low frequencies. In some cases, the flux barrier can be configured so that curve 2006 and / or crossover point 2005 can be moved as far to the left as possible by adjusting, for example, the material ratio (e.g., the ratio of conductive material in the loop to the magnetically permeable material in the core), the material itself, the layering of the material (e.g., a single material or a combination of materials), the orientation or geometry of the material layer relative to the magnetic interface (e.g., depth, width, and relative proximity to the air gap). For example, even if the shielding pole of curve 2006 is made of a 10:90 ratio of copper to rotor core, curve 2006 can become curve 2008, which has a shielding pole made of a 66:33 ratio of copper to rotor core.

[0225] In addition, the structure of the flux barrier can also affect the performance of the motor. If the flux barrier is made of pairs of alternating conductive and magnetically permeable layers (e.g., copper and nickel) (e.g., flux barrier 1304 in FIG. 13), the relationship between generated force and frequency can be represented by curve 2010, which is closer to curve 2012 for a superconductor.

[0226] Example flux barriers inside the rotor 21-23 show another rotor 2100 having a flux barrier 2104 with a conductive element below the surface of the ferromagnetic rotor material. As shown in FIG. 22, the rotor body 2102 is made of a stack of laminations of ferromagnetic material. These laminations are separated from each other at least at the rotor surface by interfaces that are less conductive than the ferromagnetic material. The interfaces may be current-restricting. The stack defines holes 2107 extending along its length and intersecting the interfaces.

[0227] 23, each flux barrier includes a conductive structure having at least two conductive bands 2110 (four shown) that penetrate each layer of the stack to intersect each interface of the stack and are electrically connected to each other at opposite ends of the stack by conductive plates 2108 to form at least one conductive loop within the rotor. Each conductive band is inserted or cast into a corresponding well 2107 in the stack of rotor plates and may then be welded or soldered to the plates 2108. Referring back to FIG. 21, each conductive structure , together with the portion of the ferromagnetic plate between and immediately surrounding the conductive bands, form a magnetic flux barrier 2104 between two adjacent rotor poles 2106 .

[0228] 24-26A show another rotor 2400 having a flux barrier 2410 with a conductive element within the rotor's ferromagnetic material. Similar to rotor 600 of FIG. 6, rotor body 2402 can be made of a stack of laminations of ferromagnetic material. These laminations are separated from each other at least at the rotor's surface by interfaces that are less conductive than the ferromagnetic material. The interfaces can be current-restricting. Rotor 2400 defines a central bore 2401 in rotor body 2402. Bore 2401 can be similar to bore 605 of FIG. 6, and an output shaft (e.g., output shaft 107 of FIG. 1) can be inserted into bore 2401 and can move with rotor 2400.

[0229] 25, the rotor body 2402 defines a series of spaced apart rotor poles 2404 forming the radially outermost portion of the rotor body, with adjacent poles 2404 defining slots 2406 therebetween. The rotor body 2402 also defines holes 2408 extending parallel along its length.

[0230] Instead of filling the slots 2406 between adjacent rotor poles 2402, each of the flux barriers 2410 includes a conductive element that forms at least one loop spanning the magnetically active extent of the rotor body 2402 below the rotor surface. As shown in FIG. 26, the conductive structure of each flux barrier 2410 includes multiple loops 2412, 2414, 2416 of conductive material that are insulated from one another outside the ferromagnetic material of the rotor body 2402. As shown in FIG. 26A, each loop (e.g., loop 2416) includes at least two conductive bands 2418 electrically connected to one another at opposite ends of the stack by a conductive plate 2420. When assembled, each of the conductive bands extends along a corresponding hole 2408 in the rotor body, as shown in FIG. 25. The plate 2420 may have a curved shape with both ends over the magnetically active extent of the adjacent rotor poles 2404. The curved shape may be based on the shape of the slot 2406. 24, the loops 2412, 2414, 2416 of the flux barrier 2410 may be arranged in series toward the slot 2406. In a sense, the conductive loop structure of each flux barrier extends into or across adjacent portions of adjacent rotor poles.

[0231] The flux barriers 2410 are electrically isolated from one another outside the ferromagnetic material. Adjacent flux barriers 2410 are preferably positioned such that any conductive path defined in the conductive material of one flux barrier does not enclose any portion of any conductive path defined in the conductive material of another flux barrier. The flux barriers 2410 may function as magnetic flux shields.

[0232] During operation, transient electromagnetic fields attempting to penetrate the ferromagnetic material enclosed by bands 2418, 2420 (and outer bands) can cause currents to flow within these bands, and this resulting current can effectively block magnetic flux from penetrating the enclosed region. The magnetic flux then follows narrow channels between segments 2416, 2414, 2412, resulting in a low-reluctance path flanked by high-reluctance paths. The region enclosed by flux barrier 2410 is blocked from magnetic propagation, resulting in distinct low- and high-reluctance paths. Forces act not on the air gap between the stator and rotor poles, but rather on the shielded / unshielded regions within the rotor (e.g., as shown in FIG. 15 ). The interface between the enclosed core region and the unenclosed region can be considered a pseudo-core interface.

[0233] 1. Exemplary Flux Barrier for a Pole with Multiple Discrete Teeth The toothed stator-rotor interface of the motor can be created to maximize torque as a function of surface area at the stator-rotor interface. Conventional motors are typically limited by their torque as a function of surface area due to relatively weak magnetic field interactions. Multiple discrete teeth on each pole and effectively reducing the tooth spacing of motors of the same pole increases the number of cycles that a pole can be energized for a given distance traveled. Specifically, by placing multiple teeth on a single pole, the force as a function of surface area can be increased.

[0234] Despite achieving higher prescriptive force for a given surface area, the higher power density in such designs can be limited due to significant leakage flux. One of the primary sources of this leakage flux comes from the air gaps between the teeth, which progressively decreases as the number of teeth increases. Therefore, to increase motor performance using a motor with multiple tooth poles, the increased prescriptive force generated by increasing the number of teeth can be used at lower current loads. Under this approach, the motor maintains a relatively small number of total poles in the system but can provide an increased number of switching cycles by allowing the surface geometry on each pole to provide more electrical cycles per pole arc. Specifically, a given prescriptive force can be generated in a pole with a magnetomotive force (MMF) of 400 to 700 amperes per turn, while a typical pole would require 3,000 to 4,000 amperes per turn of MMF to support the same force. Since smaller amperes x turns require less space, this allows motors utilizing a multi-slot approach with proportionally smaller yokes and windings to be operated at higher frequencies to achieve gains in torque, power and torque density.

[0235] The relationship between stator and rotor teeth is preferably between 0.6:1 and 1.4:1, more preferably between 0.8:1 and 1.2:1. For conventional slots, the tooth width to air gap ratio is preferably greater than 10:1, more preferably between 30:1 and 100:1 for direct drive traction applications, and 30:1 for high speed applications. For stator poles, the number of teeth per pole is preferably between 20 and 90%, more preferably between 40 and 80%, of the number of teeth per pole that maximizes the force for a given air gap.

[0236] For a given air gap, it is preferable to obtain peak force with fewer than the maximum integer number of teeth (e.g., about 50-80% of the maximum). After the peak force, the force gain begins to asymptotic and becomes relatively negligible. For a particular air gap in a motor design, the number of teeth per hole can consider more factors for optimizing force. For example, increased air slots can cause additional leakage flux and reduced saliency. Also, fewer and larger poles allow for greater power density and handle higher current loads that may lead to saturation. Additionally, as discussed below, tooth slots can be filled with diamagnetic material, which can also affect motor performance.

[0237] For a given pole, the maximum inductance remains the same as the tooth size decreases and the number of teeth increases, but the minimum inductance increases due to the smaller permeability of air in the slot. Thus, the total energy per cycle decreases as the number of teeth per pole increases.

[0238] FIG. 27 shows a motor 2700 including a plurality of discrete teeth on each pole of the motor. The motor 2700 includes a stator 2710 and a rotor 2720. The outer surfaces of the stator 2710 and the rotor 2720 define an air gap 2715. The motor 2700 is similar to the motor 400 of FIG. 4 except that each stator pole 2712 of the stator 2710 includes a plurality of teeth 2714 with slots 2716 therebetween, and each rotor pole 2722 of the rotor 2720 includes a plurality of teeth 2724 with slots 2726 therebetween. Note that slots 2718 may exist between adjacent stator poles 2712, while the rotor 2720 may include continuously alternating teeth 2724 and slots 2726 along the outer surface of the rotor 2720.

[0239] The magnetic flux barriers are formed between adjacent rotor teeth 2724 and / or adjacent stator teeth 2714. The flux barrier may be similar to flux barrier 704 of FIG. 7, flux barrier 1104 of FIG. 11, flux barrier 1304 of FIG. 13, or flux barrier 1404 of FIG.

[0240] The flux barrier material can be an inductive material that has greater diamagnetic properties than air during operation to increase the total energy per cycle. This creates a dynamic flux barrier. Using the impedance of an inductor to provide such diamagnetic properties results in a larger saliency ratio during low, medium, and high frequency (e.g., 2 Hz to 1 MHz) operation. As discussed above, this can be achieved by using the skin effect of an all-metal monolithic material such as aluminum, copper, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, or carbon nanotubes, or more preferably, a superconductor. Superconductors can be operated at frequencies above 0.5 Hz, while copper can be operated at medium to high frequencies from 20 KHz to 1 MHz. In other embodiments, ferromagnetic composite materials such as copper-iron, nickel-iron, lead-iron, brass-iron, silver-iron, zinc-iron, gold-iron, bismuth-iron, aluminum-iron, pyrolytic graphite-iron, graphene-iron, carbon nanotube-iron, or Alinco (aluminum-nickel-cobalt) alloy may be used, which can operate between 100 Hz and 20 kHz. In other embodiments, higher inductance filler materials may be used to create equivalent impedances (such as constructing loop poles or shield poles (e.g., copper-shielded iron poles) at low frequencies). Such combinations of diamagnetic and ferromagnetic materials approximate the properties of metamaterials. Structurally, as this slot filling begins to approximate the smooth, continuous surfaces of the rotor and stator faces and the tooth dimensions decrease, such slot filling materials can act as mechanical supports to prevent physical deformation caused by forces generated during operation.

[0241] As the teeth become smaller on a given pole, the slots can be closer together, and the resulting leakage flux reduces both the saliency ratio and the work per cycle (and therefore torque). By replacing air with a material that approximates a diamagnetic material (e.g., a single diamagnetic material or a combination of diamagnetic and ferromagnetic materials), it is possible to increase the number of motor teeth as an effective electromagnetic reduction, similar to a gearbox. While the energy per cycle, and therefore torque, decreases as a result of increasing the number of teeth per pole for a given pole size, torque and power density can be achieved by increasing the saliency ratio using diamagnetic materials. A further advantage of pole designs or configurations with diamagnetic slot filling, in particular, is that the magnetic field over poles with a large number of teeth is generated in a single direction over a given pole, as opposed to the constant reversing magnetic field in a typical motor.

[0242] As discussed above in Figure 20, at low frequencies, the generated effective force remains constant or flat with frequency because the diamagnetic flux barrier appears like air and therefore has no or little effect. At intermediate to high frequencies, the flux shielding effect begins to become more dominant, and the force continues to increase with increasing frequency. Therefore, by filling the slots with diamagnetic flux barriers, lower drive currents (and therefore fewer windings) can be used, thus saving money by using less wire and increasing efficiency by reducing ohmic losses. Furthermore, motor performance can be further improved by using higher drive currents (e.g., through saturation). Slot depth also affects the horizontal force generated. The resulting force can be substantially proportional to the slot depth along the direction perpendicular to the air gap.

[0243] Axial gap motor with flux barriers. 28 is a perspective view of an example axial gap motor 2800 having flux barriers between adjacent rotor poles. The axial gap motor 2800 has a rotor 2804 disposed parallel to a stator 2802. The rotor 2804 defines a central bore 2801, and an output shaft can be disposed within the central bore 2801 such that the rotor 2804 is rotatable therewith.

[0244] The rotor 2804 is movable relative to the stator 2802 by rotation about the rotor's axis of rotation (or the axis of rotation of the output shaft). The end faces of the rotor 2804 are perpendicular to the rotor's axis of rotation. The end faces of the rotor 2804 are spaced apart from the end faces of the stator 2802 along the axis of rotation to define a nominal gap 2803. The nominal gap 2803 is the axial gap between the end faces of the stator 2802 and the rotor 2804 and along the rotor's axis of rotation.

[0245] The stator 2802 defines a series of stator poles 2810, each including a stator pole core 2812 surrounded by an associated electrical winding 2814. The electrical windings 2814 of the stator 2802 are independently energizable and are spaced circumferentially about the stator. The rotor 2804 has a series of rotor poles 2820 with magnetic flux barriers 2830 therebetween. Each magnetic flux barrier 2830 has a conductive loop surrounding a core of magnetically permeable material. The magnetic flux barriers, rotor poles, and rotor back plate core may all be part of a series of ferromagnetic material (e.g., formed by pressed and sintered powder). The conductive loops of the flux barriers may be, for example, copper rings pressed onto the core.

[0246] 29-32 show various views of another axial gap motor rotor 2900. Rotor 2900 has a flat active end face (facing the stator, not shown) that includes pole surface areas that form rotor poles 2920 and inter-pole surface areas that are formed between the pole surface areas by flux barriers 2930. In this example, flux barriers 2930 are shield poles, similar to shield poles 1404 of FIG.

[0247] Each flux barrier 2930 includes a conductive material that forms a loop 2932 centered around a core 2934 of the core material. The core material has a higher magnetic permeability than the conductive material. The core material may be ferromagnetic. The core material of the core 2934 and the pole material of the rotor poles 2920 may be the same, with the core 2934 and rotor poles 2920 forming a continuous overall rotor body (e.g., of sintered iron powder). The conductive material of the flux barrier may be cast into the formed rotor core.

[0248] 29-32, each loop 2932 includes five loop portions 2932a, 2932b, 2932c, 2932d, and 2932e. Loop portion 2932a forms a portion of the end face of rotor 2900.

[0249] Loop portion 2932b extends to a depth along a direction parallel to the axis of rotation and forms part of the outer radial surface of rotor 2900. The end faces are perpendicular to the outer radial surface. Loop portion 2932c extends to a depth along a direction parallel to the axis of rotation and forms part of the inner radial surface of rotor 2900. The depth of loop portion 2932c can be the same as the depth of loop portion 2932b.

[0250] Loop portions 2932d, 2932e extend radially from the rotor's inner radial surface to the rotor's outer radial surface to form a shielding wall between adjacent rotor poles 2920 and core 2934. Loop portions 2932d, 2932e also extend into the rotor body to an extent having a depth that may be the same as the depth of loop portions 2932b, 2932c. Each of the loop portions may have a thickness that is consistently the same (preferably greater than the current skin depth of the conductive material of loop 2932 at a particular operating frequency).

[0251] Stator with flux barriers Flux barriers may also be provided in the stator of the motor to further increase performance.

[0252] Figure 33 shows a stator 3300 having flux barriers 3320 disposed between stator poles 3310. The stator poles 3310 may be housed within a magnetically permeable yoke 3302 or may be separated from the magnetically permeable yoke. The stator poles 3310 may be connected to the yoke 3302. Each stator pole 3310 includes a stator core 3312 surrounded by an associated electrical winding 3314. The stator core 3312 (and yoke) may be made of a stack of layers of ferromagnetic material extending along the longitudinal axis. The layers are separated from each other by interfaces that are less electrically conductive than the ferromagnetic material. The stator core 3312 may be a stator protrusion that protrudes from the yoke 3302.

[0253] Each flux barrier 3320 forms a flux shield that extends along both edges of the stator pole 3310 and is formed of a material having a higher electrical conductivity than the ferromagnetic material of the stator core 3312. The flux barriers 3320 may extend into the gaps between adjacent electrical windings 3314. As shown in FIG. 34 , the flux barriers 3320 may extend from an air gap 3350 to the yoke 3302 connecting adjacent stator poles 3310. The air gap 3350 is defined between the two outer surfaces of the stator 3300 and the rotor 3400. The rotor 3400 includes a series of rotor poles 3410 having flux barriers 3420 therebetween, as discussed above.

[0254] 33 and 34, each stator core 3312 surrounded by electrical windings 3314 has an angular width W0 along the circumference of the stator 3300. The flux barriers 3320 extend into notches in the face of the stator core 3312 such that the angular width W1 of the stator core 3312 in the air gap between the edges of adjacent flux barriers 3320 is less than the angular width W0 of the stator core 3312 surrounded by the electrical windings 3314. That is, W1 <W0である。

[0255] FIG. 35 illustrates another stator 3500 having magnetic flux barriers 3520 disposed between stator poles 3510. Similar to the stator 3300 of FIGS. 33-34, each stator pole 3510 includes a stator core 3512 surrounded by an associated electrical winding 3514. The stator core 3512 may be a stator protrusion formed as a stack of magnetically permeable plates having current-suppressing interfaces and projecting from a magnetically permeable yoke 3502. Each magnetic flux barrier 3520 is formed of a material having a higher electrical conductivity than the material of the stator core 3512 and intersects the stack interfaces. As shown in FIG. 36, the magnetic flux barriers 3520 may extend from an air gap 3550 to the yoke 3502, connecting adjacent stator poles 3510 across the air gap 3550 defined between the stator 3500 and the rotor 3600. The rotor 3600 includes a series of rotor poles 3610 with flux barriers 3620 therebetween, as discussed above.

[0256] Motor 3500 differs from that of Figures 33-34 in that the angular width of the stator core is approximately constant from the air gap to yoke 3502, i.e., W0 = W1.

[0257] FIG. 37 illustrates another stator 3700 having magnetic flux barriers 3720 disposed between stator poles 3710. Similar to the stator 3300 of FIGS. 33-34, each stator pole 3710 includes a stator core 3712 surrounded by an associated electrical winding 3714. The stator core 3712 may be a stator protrusion projecting from a magnetically permeable yoke 3702, with the stator core and yoke formed as a stack of ferromagnetic plates with current-suppressing interfaces. Each magnetic flux barrier 3720 is formed of a conductive material and intersects at least a majority of the ferromagnetic plate interfaces of the stator core. As shown in FIG. 38, the magnetic flux barriers 3720 may extend from the inner surface of the stator 3700 to the yoke 3502 connecting adjacent stator poles 3710.

[0258] The stator core 3712 has longitudinally continuous tabs that are received in corresponding slots in the flux barriers 3720. After the windings are assembled on the core, the flux barriers can be inserted longitudinally and held in place by the tabs on the stator core, further securing the windings.

[0259] Linear motor with magnetic flux barrier As discussed above, flux barriers can be configured in radial gap motors and axial gap motors where the rotor poles and / or stator poles are circumferentially arranged. and / or linear motors are discussed in which the stator poles are arranged linearly and the relative motion between the stator and rotor is along a straight line and the magnetic flux barriers are arranged linearly.

[0260] 39 and 40 show an example linear motor 3900 including a stator 3910 and a rotor 3950. The rotor 3950 is movable relative to the stator 3910 along the direction of motion and defines with the stator 3910 a nominal gap 3940 having a width perpendicular to the direction of motion.

[0261] The stator 3910 defines a series of stator poles 3920 linearly arranged along the direction of motion and linearly connected by a magnetically permeable yoke or back plate 3902. Each stator pole 3920 includes a stator core 3922 surrounded by an associated electrical winding 3924. The stator core 3922 may be made of a stack of layers of ferromagnetic material, each extending along the direction of motion. The layers are separated from each other by interfaces that are less electrically conductive than the ferromagnetic material. The stator cores 3922 may be stator lugs that protrude from the yoke 3902. The stator lugs define slots 3930 therebetween.

[0262] The rotor 3950 includes a series of rotor poles 3960 spaced apart along the direction of motion with magnetic flux barriers 3970 between them. The magnetic flux barriers 3970 may be shielding poles similar to the magnetic flux barriers 1504 in FIG. 15 . Each magnetic flux barrier 3970 is made of a conductive loop 3972 centered on a magnetically permeable core 3974 between adjacent rotor poles 3960. The rotor poles 3960 may be made of a laminated stack of layers of ferromagnetic material separated from each other by interfaces that are less conductive than the ferromagnetic material. The magnetic flux barriers 3970 each have a flat outer surface parallel to the direction of motion and form inter-pole surface areas between the pole surface areas of the rotor poles 3960. The inter-pole surface areas and the pole surface areas define the outer surface (or end face) of the rotor 3950. Each core 3974 forms a portion of the outer surface surrounded by a respective loop 3972. The loops 3972 may be made of a conductive, low-energy material such as copper. The material of the core 3974 is more magnetically permeable than the material of the loops 3972. The material of the core 3974 and the ferromagnetic material of the rotor poles 3960 may be adjacent parts of a stack of layers. The loops 3972 of the flux barriers 3970 do not overlap and are electrically isolated from each other outside the ferromagnetic material. The flux barriers 3970 are electrically connected to each other only through the ferromagnetic material whenever possible.

[0263] 41 and 42 show another example linear motor 4100 including a stator 4110 and a rotor 4150, each having a plurality of tooth poles as described above with respect to FIG. 27, but with the conductive material between the teeth forming loops. The rotor 4150 is movable relative to the stator 4110 along the direction of motion and defines with the stator 4110 a nominal gap 4440 having a width perpendicular to the direction of motion.

[0264] Similar to the stator 3910 of FIGS. 39-40, the stator 4110 defines a series of stator poles 4120 linearly arranged along the direction of motion and linearly connected by a magnetically permeable yoke or back plate 4102. Each stator pole 4120 includes a stator core 4122 surrounded by an associated electrical winding 4124. The stator core 4122 may be made of a stack of layers of ferromagnetic material, each extending along the direction of motion. These layers are separated from each other by interfaces that are less electrically conductive than the ferromagnetic material. The stator core 4122 may be stator protrusions that protrude from the yoke 4102. The stator protrusions define slots 4130 therebetween. Unlike the stator 3910, the stator poles 4120 (or stator core 4122) include, on at least the outer surface of the stator poles 4120, a plurality of teeth 4122a with slots 4122b therebetween. As discussed above, magnetic flux barriers are formed in the slots 4122b between multiple stator pole teeth 4122a. In the configuration shown, the material in the two left slots 4122b of each stator pole forms a loop around the left stator tooth 4122a, and the material in the two right slots forms a second loop around the right stator tooth 4122a. In this configuration, The two loops act to shield magnetic flux penetration through the outer two stator pole teeth. Alternatively, the conductive material filling each of the inter-tooth slots 4122b acts as a separate local magnetic flux reflector through the effect of eddy currents set up in the conductive material (without forming loops with the material of adjacent slots). As another alternative, each slot 4122b itself may include a shielding pole flux barrier.

[0265] The rotor 4150 includes a series of rotor poles linearly arranged along the direction of motion. Each rotor pole includes multiple teeth 4160 with flux barriers 4170 in slots between adjacent teeth 4160. Each flux barrier 4170 may be a shield pole, similar to the flux barriers 3970 in FIG. 39 . Each flux barrier 4170 is made of a conductive loop 4172 centered on a magnetically permeable core 4174 between adjacent rotor pole teeth 4160. The loop 4172 may be made of a conductive, low-energy material. The core material of the core 4174 has a higher magnetic permeability than the material of the loop 4172. The core material of the core 4174 and the ferromagnetic material of the rotor poles 4160 may be adjacent parts of a stack of layers. The loops 4172 of the flux barriers 4170 do not overlap and are electrically isolated from each other outside the ferromagnetic material. The flux barriers 4170 may be connected to each other only through the ferromagnetic material.

[0266] Operation of a motor with a flux barrier The effect of the magnetic flux barrier may vary depending on the horizontal force at various frequencies. As shown in Figure 20, the horizontal force may begin to increase above the cutoff frequency (e.g., 10 Hz), and the horizontal force may increase at low frequencies (e.g., 10 Hz) and high frequencies (e.g., 10 5 The increase between 1000 and 2000 Hz can exceed an order of magnitude. At high frequencies, the flux barriers can exhibit stronger diamagnetic properties to concentrate the magnetic flux toward the rotor poles and increase the component of force along the direction of motion.

[0267] The effective force can also be affected by operating conditions. Under saturated conditions and at high frequencies, the flux barriers may exhibit stronger diamagnetic properties (compared to unsaturated conditions) to concentrate the magnetic flux toward the rotor poles. The effective force may continue to increase as frequency increases. For example, at high frequencies (e.g., 105 Hz), the horizontal force may increase by two orders of magnitude as the drive current increases from 10 amperes per turn (corresponding to unsaturated operating conditions) to 200 amperes per turn (corresponding to saturated operating conditions).

[0268] As noted above, the number of teeth per pole can also affect the effective force. Increasing the number of teeth per pole can cause a gradual increase in force. However, as the gap size becomes larger (e.g., to 1.0 mm), the force can decrease as the number of teeth per pole increases.

[0269] For configurations with flux barriers, each pole pair can be operated under pulsed-DC or pulsed-AC current.

[0270] This operation utilizes a high inductance and low resistance magnetic flux barrier, resulting in a high reactance that is in phase with the magnetic field. As the magnetic field travels up the primary coil and reluctance teeth, it is reflected back through the shielding teeth, resulting in a high impedance to the magnetic field. The system can be operated via an alternating magnetic signal through only a 50% duty cycle (e.g., from a non-aligned position to an aligned position). Continuing through the duty cycle (e.g., from a non-aligned position to an aligned position) can produce a counter torque.

[0271] A higher reactance flux barrier may also enable a higher power factor system that can generate torque more efficiently compared to conventional machines. A high reactance, high impedance flux barrier design may prevent nearly all of the magnetic flux from penetrating the flux barrier over the entire work cycle. In this way, the motor can operate at a wide range of temperatures (e.g., from room temperature to high temperatures) in a superconducting motor. These motors can benefit from diamagnetic properties previously only experienced in motors with high current density. This may also be less sensitive to temperature compared to permanent magnet motors, which tend to demagnetize above a critical temperature.

[0272] The motor with the flux barrier can be dynamically driven with a square-wave current. If the motor is dynamically driven, a square wave can be used at a switching frequency relatively lower than an equivalent sine wave to induce a large reactance in the flux barrier while pulsating at a relatively low frequency (such as 50 Hz). This is due, in part, to the high proportion of harmonics in a square wave as opposed to a sine wave. This also reduces the switching losses required by power electronics due to the high frequency required by pulse-width modulation (PWM) switching. In such operation, relatively thin (e.g., 0.127 mm) laminations can be used to reduce eddy current losses in iron cores and low gauge (e.g., 0.2 mm), and even Litz wire windings can be utilized in the primary coil to reduce skin effect losses in the core winding.

[0273] The motors described above can also benefit from higher winding efficiency for the coils. While typical slot-fill ratios for windings are 30-40% of a given slot area, by utilizing casting techniques to fill the flux barriers in the slots between adjacent poles, the motor can utilize nearly all (e.g., 85-95%) of the slot volume for the flux barriers. This can reduce the total amount of wire required for the motor's primary winding, thus allowing the primary winding to use fewer turns of wire compared to a typical motor.

[0274] As noted above, filling the slots with diamagnetic flux material presents a means of concentrating magnetic flux during motor operation. Specifically, when the stator and rotor are misaligned, significant internal electromagnetic reflections block most of the magnetic propagation from the opposing pole surfaces. This diamagnetic shielding allows the magnetic slots to effectively push the rotor, while the reluctance of the electromagnetic poles pulls the rotor. This effect allows more energy to be produced from the system per cycle, similar to the effect that permanent magnets can produce in some configurations.

[0275] This effect provides a significant advantage over permanent magnets, which can suffer from demagnetization due to high eddy currents. This effect can be seen in a BH curve, which examines the coercivity of a permanent magnet. In the motor described above, a high-reactance flux barrier can approximate an opposing permanent magnet with infinite coercivity. Thus, the flux barrier can reflect an applied magnetic field to achieve field levels beyond those achievable in a typical permanent magnet motor, generating a large back EMF and thereby increasing torque density, power density, and efficiency. Furthermore, while permanent magnets demagnetize at elevated temperatures as described above, the flux barrier can be constructed of materials that can withstand temperatures over 100 degrees Fahrenheit higher than typical permanent magnets.

[0276] Furthermore, while permanent magnets generate a constant magnetic field, diamagnetic flux barriers exist dynamically in transient conditions. This has advantages for both efficiency and safety, as permanent magnet motors can experience dent, cogging, and braking torques that can be catastrophic at times due to EMFs that can be generated regardless of the power available. The motor can be controlled to effectively coast for long periods of time, with losses only from bearing resistance.

[0277] Furthermore, unlike an IM, which has an active inductive load that produces a continuous current, the current in each flux barrier is allowed to return to near zero with each cycle. The higher the motor's operating frequency, the less current required at each flux barrier to maintain reflection. Because the system is reactive, energy is elastically returned or converted into rotor kinetic energy within each switching cycle.

[0278] The diamagnetic flux barrier slot filling can be dynamically adjusted for a given application and during operation. Unlike air, the magnetic properties of the system can be adjusted in both the amplitude of the magnetomotive force (MMF) at a given location and the frequency of the MMF. This allows for real-time adaptation by weakening or strengthening the magnetic flux properties of the system by changing the motor's switching frequency. This can change the back EMF on the primary coil, which can allow the motor to achieve a wider speed range than conventional motors. Conventional motors have a fixed back EMF based on a fixed saliency ratio that is used to change the magnitude of the magnetic field. The motor can change the magnitude of the magnetic field in addition to the activation frequency of the motor's operation.

[0279] At high speeds, the motor can operate as a reactive reluctance motor. In conventional SRM operation, a peak voltage is applied at the beginning of a misalignment position of the stator and rotor (or stator-rotor teeth), and the current is rapidly increased until the stator and rotor (or stator-rotor teeth) reach an alignment point. At this point, a reverse voltage is applied and the current drops to zero. In a locked rotor (stator-rotor teeth) condition in a conventional SRM, the current is applied continuously rather than pulsed. In motors with flux barriers, the current is pulsed through the active coils during stall. When the pole switching frequency exceeds the flux barrier crossover frequency during motor acceleration, each pole is excited by a single pulse.

[0280] Exemplary Process An embodiment of the present disclosure provides a method for driving an electric motor, which may be electric motor 102 of FIG. 1, and the method may be performed by a motor controller (e.g., motor controller 104 of FIG. 1).

[0281] During operation, the motor controller energizes a first active pole of a series of active poles disposed along an air gap between the series of active poles and a passive magnetic component having a series of passive poles disposed along the air gap by pulsing current through an electrical winding associated with the first active pole. The pulsed current includes a series of at least three pulses in which adjacent active pole windings of the series of active poles are not energized. Pulsing the current through the electrical winding associated with the first active pole passes current through the electrical winding associated with the first active pole according to a current waveform in which the ratio of maximum current to minimum current during pulsing of the current through the electrical winding associated with the first active pole is at least 4:1, 7:1, or even 10:1.

[0282] In some cases, the electrical winding associated with the first active pole includes multiple coils conductively connected in parallel to and wound on a common core, and the motor controller can pulse current through the multiple coils conductively connected in parallel.

[0283] In some examples, the motor controller pulses current through the electrical winding associated with the first active pole by operating a first switch to open and close in multiple cycles between the voltage source and the electrical winding associated with the first active pole. The first switch may be associated with and conductively coupled to the first active pole. The first switch may be switch 134 of FIG. 2 or power switch 200 of FIG. 2A.

[0284] After the first active pole is energized (with multiple current pulses), the motor controller energizes a second active pole of the series of active poles by pulsing current through an electrical winding associated with the second active pole. The pulsed current for the second active pole includes a series of at least three pulses during which the winding of the first active pole is not energized, passing current through the electrical winding associated with the second active pole according to a current waveform in which the ratio of maximum current to minimum current during the pulsing of current through the electrical winding associated with the second active pole is at least 4:1, 7:1, or even 10:1.

[0285] The first active pole can be energized by pulsing the current at a pulse frequency between 2 Hz and 1 MHz, in some cases between 10 Hz and 20 kHz, and in some cases between 100 Hz and 5 kHz. Energizing the first active pole and subsequently energizing the second active pole generates a first force between the first active pole and the passive pole across the air gap from the first active pole, and a second force between the second active pole and the passive pole across the air gap from the second active pole. The first and second forces can induce relative motion between the active pole and the passive pole. The relative motion can include motion of a passive magnetic component relative to the active pole.

[0286] In some examples, the passive magnetic component is a rotor of a motor, and the relative motion includes rotation of the rotor. The motor controller may further detect rotor speed and control the frequency (or pulse frequency) of the pulsed current in response to the detected rotor speed. The motor controller may further maintain the current pulse frequency during rotor speed changes, at least up to a rotor speed at which the frequency at which each active pole is energized is at least half the pulse frequency. Current may be pulsed through the electrical windings associated with the first and second poles only below a rotor speed corresponding to one pulse per pole energization.

[0287] After energizing the second active pole, the motor controller may further energize a third active pole in the series of active poles located opposite the second active pole rather than the first active pole by pulsing current through an electrical winding associated with the third active pole, including a series of at least three pulses in which the windings of the first and second active poles are not energized. After energizing the third active pole, the motor controller may again energize the first active pole by pulsing current through an electrical winding associated with the first active pole, and thereafter re-energize the second active pole by pulsing current through an electrical winding associated with the second active pole, and thereafter re-energize the third active pole, etc.

[0288] As noted above, the magnetic flux barriers may be implemented within passive magnetic components. In some examples, pulsing current through an electrical winding associated with a first active pole generates eddy currents within a first magnetic flux barrier adjacent to the passive pole across the air gap from the first active pole. The magnetic flux barrier has a higher conductivity than the passive pole across the air gap. The passive magnetic component may further include a second magnetic flux barrier, and the passive pole across the air gap from the first active pole is disposed between the first and second magnetic flux barriers. The first and second magnetic flux barriers are electrically isolated from each other outside the passive pole.

[0289] In some motors, the passive poles are formed by a stack of layers of magnetically permeable material. Eddy currents in the first flux barriers act to direct magnetic flux away from the first active pole. In some examples, the first flux barriers are positioned between the passive poles across the air gap from the first active pole and adjacent passive poles, and the flux barriers form loops of conductive material around a core of core material that has a higher magnetic permeability than the conductive material.

[0290] In some cases, the passive magnetic component further includes a flux barrier between adjacent pairs of passive poles in the series of passive poles, each of which includes a conductive material different from the material forming the passive pole and defines at least one conductive path around the magnetically permeable core. The flux barriers are electrically isolated from each other outside the series of passive poles. Adjacent flux barriers may be positioned such that any conductive path defined in the conductive material of one flux barrier does not enclose any portion of any conductive path defined in the conductive material of another flux barrier.

[0291] In some embodiments, the motor further includes a flux shield extending along opposite edges of each active pole, the flux shield being formed of a material having a higher electrical conductivity than the material of the active magnetic component disposed between the flux shields. The flux shields may extend into gaps between adjacent electrical windings. The flux shield may extend from the air gap to a magnetically permeable yoke connecting adjacent active poles.

[0292] Exemplary Cooling and Thermal Relaxation Electric motors generate significant heat during operation, especially during high-frequency operation, and may require cooling. Active cooling systems may be used to provide intermittent or continuous cooling of the surfaces by circulating a fluid coolant through the motor. The cooling system may be a cooling system such as that described in co-pending patent application U.S. Patent Application No. 62 / 675,207, entitled "Electric Motor," filed March 23, 2018, which is expressly incorporated herein by reference in its entirety.

[0293] Also, the efficiency and power output of the flux barrier can be increased for a given frequency if the operating temperature is reduced. Typical operating conditions are -80°C to 300°C. Coolant can be added to the motor system to further reduce the temperature and increase the diamagnetic properties of the flux barrier.

[0294] The coolant can be any conventional fluid used for thermal mitigation. At operating conditions, the coolant can be a low viscosity fluid (such as water or motor oil) in the range of 1 to 500 centipoise, which allows for both high cooling efficiency and high rotational dynamics. The coolant not only provides damping for vibrations generated during operation, but also provides restoring force to harmonics generated at high rotational speeds.

[0295] Active cooling can enable greater power density by providing a medium for absorbing heat from electrical coils and mechanical contact surfaces. Active lubrication systems can be used to provide intermittent or continuous lubrication of surfaces by circulating a fluid lubricant within the motor. For example, a fluid pump can mechanically encourage lubricant to flow from the fluid pump to the motor through fluid lines, and the lubricant can be ejected through directional nozzles to provide active lubrication and / or fluid cooling to specific locations within the motor. The fluid can then gravitationally collect in an oil pan at the base of the motor and return to the pump through fluid lines for recirculation. In this way, the motor rotor assembly can operate in a cool, non-immersed environment. Additionally, a portion of the lubricant can pass through a heat exchanger to add or remove heat from the lubricant to modulate the temperature and / or viscosity of the lubricant to meet the specific needs of the application.

[0296] The coolant can be any conventional fluid used for thermal mitigation. At operating conditions, the coolant can be a low viscosity fluid (such as water or motor oil) in the range of 1 to 500 centipoise, which allows for both high cooling efficiency and high rotational dynamics. The coolant can provide damping for vibrations generated during operation, as well as restoring forces to harmonics generated at high rotational speeds.

[0297] The motor may include a collection pan for gravitationally collecting refrigerant released within the motor assembly and directing it toward the return fluid line.

[0298] The coolant system may include a fluid pump that provides a pressure gradient to the coolant, causing it to circulate within the fluid system. Such a pump may be a fixed displacement pump, such as a rotary pump, or a variable displacement pump, such as a gear or piston pump. The pump may be operably connected to a source of mechanical or electrical power and may operate continuously or intermittently during motor operation. A wet sump active lubrication system may include a single fluid pump operably connected to a collection pan to circulate oil through the fluid lines and the cooling system. In this case, the majority of the oil supply is in the collection pan. Alternatively, multiple fluid pumps may be operated in a dry sump active cooling configuration, in which fluid from the collection pan is continuously pumped into a storage tank, preferably having a high height relative to its cross-sectional area, and a second pump may pump fluid back to the motor under another controlled flow rate to complete the coolant circulation.

[0299] The coolant system may be configured to direct coolant to specific locations within the motor assembly, including, for example, the stator poles. The nozzle may have one or more directional nozzles.

[0300] Other embodiments Any of the motors described above can be controlled to generate electrical energy from kinetic energy (e.g., to regeneratively brake the motor). This can be achieved by timing the excitation signal so that the stator current is pulsed at the point of minimum air gap (or even slightly delayed from the point of minimum air gap) to generate a forward EMF during extension. In this way, even though the motor cannot be mechanically back-driven by torque applied to the output shaft, current is generated and directed to storage in an associated battery, while a deceleration torque is applied to the rotor to slow the motor.

[0301] Any of the motors described above can be controlled to generate electrical energy from kinetic energy (e.g., to regeneratively brake the motor). This can be achieved by timing the compression wave so that the stator current is pulsed at the point of minimum air gap (or even slightly delayed from the point of minimum air gap) to generate a forward EMF during extension. In this way, even though the motor cannot be mechanically back-driven by torque applied to the output shaft, current is generated and directed to storage in an associated battery, while a deceleration torque is applied to the rotor to slow the motor.

[0302] While many examples have been set forth for illustrative purposes, the foregoing description is not intended to limit the scope of the invention, which is defined by the appended claims. Other examples and modifications exist and will exist within the scope of the following claims.

Claims

1. An electric motor, a stator having a plurality of stator poles and electrical windings associated with the stator poles; a rotor movable relative to the stator, the rotor having a plurality of rotor poles, at least at a surface of the rotor, being a stack of layers of ferromagnetic material separated from one another by interfaces that are less electrically conductive than the ferromagnetic material, the rotor poles defining a nominal gap between the rotor poles and the stator poles; the nominal gap is an axial gap perpendicular to the axis of rotation of the rotor; the rotor has flux barriers disposed between adjacent rotor poles and formed of a material having a higher electrical conductivity than the ferromagnetic material; The electric motor, wherein the flux barriers are electrically isolated from each other external to the ferromagnetic material.

2. 2. The electric motor according to claim 1, wherein the axial gap is a gap between an end face of the rotor and an end face of the stator, and the end face of the rotor and the end face of the stator are disposed apart from each other along the rotational axis of the rotor.

3. 2. The electric motor of claim 1, wherein at least one of the magnetic flux barriers is formed by a conductive material that forms a loop annularly surrounding a core material having a magnetic permeability higher than that of the conductive material.

4. 4. The electric motor of claim 3, wherein the core material is a ferromagnetic material.

5. 4. The electric motor of claim 3, wherein said core and said rotor poles are part of one continuous piece of ferromagnetic material.

6. 4. An electric motor as claimed in claim 3, wherein said loop forms a portion of an outer radial surface of said rotor which defines said nominal clearance.

7. 7. The electric motor of claim 6, wherein the core forms a portion of the outer radial surface of the rotor surrounded by the loops.

8. 4. The electric motor of claim 3, wherein said loop is disposed below a surface of said rotor that defines said nominal gap and includes an end of said layer of ferromagnetic material.

9. 4. The electric motor of claim 3, wherein the loop has a capacitance.

10. 10. The electric motor of claim 9, wherein the capacitance is formed at a specific point along the loop.

11. 4. The electric motor of claim 3, wherein said loop has a resonant frequency within the permeability range of said ferromagnetic material.

12. 4. The electric motor of claim 3, wherein the rotor end faces have inter-pole regions with the rotor poles defining pole surface areas and the flux barriers disposed between the pole surface areas.

13. 13. The electric motor of claim 12, wherein the core and the rotor poles comprise a continuous, entire rotor body, and the conductive material of the flux barrier is cast into the core.

14. 13. The electric motor according to claim 12, The loop a first loop portion forming a portion of the end face of the rotor; a second loop portion extending to a first depth in a first direction perpendicular to the end face and parallel to the axis of rotation, the second loop portion forming a portion of an outer radial surface of the rotor; a third loop portion extending to a second depth in a second direction perpendicular to the end surface and parallel to the axis of rotation, the third loop portion forming a portion of an inner radial surface of the rotor; wherein the first depth of the second loop portion is the same as the second depth of the third loop portion.

15. 15. The electric motor of claim 14, The loop a fourth loop portion and a fifth loop portion extending radially from the inner radial surface to the outer radial surface and forming a shielding wall between adjacent rotor poles and the core; the fourth loop portion and the fifth loop portion extend into a rotor body to a third depth that is the same as the first depth of the second loop portion and the second depth of the third loop portion.

16. 16. The electric motor of claim 15, wherein each of the first through fifth loop portions has a uniform and identical thickness greater than a current skin depth of the conductive material at a predetermined operating frequency.

17. An electric motor, an active magnetic component having a first surface defining a plurality of active poles, each having a winding; a passive magnetic component having a second surface movable relative to the first surface and spaced apart from the first surface to define a gap, the second surface having a plurality of spaced apart pole surface regions formed of a first material, the pole surface regions separated by inter-pole regions formed of a second material; the passive magnetic component includes a magnetically permeable material having an internal passageway connecting opposite sides of each adjacent pole surface region; the inter-pole region is formed of a second material having a low energy product that is electrically conductive and electrically insulated from one another outside the magnetically permeable material; an electric motor, wherein the active magnetic component is a stator, the passive magnetic component is a rotor, the pole surface area and the inter-pole area form end faces of the rotor, and the gap is an axial gap perpendicular to the axis of rotation between the rotor and the stator.

18. 18. The electric motor of claim 17, wherein the end faces of the rotor are perpendicular to the axis of rotation, and the end faces are spaced apart along the axis of rotation from end faces of the stator.

19. 1. An electric drive system comprising: an active magnetic component having a first surface defining a plurality of active poles, each having a winding; and a passive magnetic component having a second surface movable relative to the first surface and spaced apart from the first surface to define a gap, the second surface having a plurality of spaced apart pole surface regions formed of a first material, the pole surface regions separated by inter-pole regions formed of a second material; the passive magnetic component includes a magnetically permeable material having an internal passageway connecting opposite sides of each adjacent pole surface region; the inter-pole region is formed of a second material having a low energy product that is electrically conductive and electrically insulated from one another outside the magnetically permeable material; a reluctance motor, wherein the active magnetic component is a stator, the passive magnetic component is a rotor, the pole surface area and the inter-pole area form end faces of the rotor, and the gap is an axial gap perpendicular to the axis of rotation between the rotor and the stator; a motor controller comprising a plurality of switches connected to respective windings or sets of respective windings of the active magnetic component.

20. 20. The electric drive system of claim 19, The motor controller: sequentially activating corresponding switches to generate magnetic flux through the flux gaps of each of the active poles; 1. An electric drive system comprising: a winding of each active pole having a current pulsed therethrough in a sequence having at least three pulses in a current-carrying duty cycle of each active pole; a winding of an adjacent active pole being controlled not to be current-carrying; and a ratio of maximum current to minimum current in the windings of at least 4:1.

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