Axial flux switching permanent magnet machine

An electric machine includes a rotor, a first and second stator, a first and second plurality of permanent magnets, a first and second winding, a third and fourth winding. The first stator and the second stator are mounted axially relative to the rotor. A first permanent magnet and a second permanent magnet of the first plurality of permanent magnets have opposite polarities. A first permanent magnet and a second permanent magnet of the second plurality of permanent magnets have opposite polarities. The first winding, the second winding, the third winding, and the fourth winding are connected in series. An absolute value of an angle offset between the first winding and the third winding and between closest poles of the first plurality of poles and the second plurality of poles is 180 electrical degrees.

BACKGROUND

The excitation frequency, fe, of a flux switching permanent magnet (FSPM) machine is proportional to the number of rotor poles (pr), fe=npr/60, and not pole pairs, where n is the rotational speed in revolutions per minute (rpm). A typical FSPM machine has 12 stator slots and 10 rotor poles resulting in a high fundamental excitation frequency when operated at high-speed. For some high speeds, the fundamental frequency may not be attainable with today's power electronic converters.

To reduce the fundamental frequency for a given rotational speed, the number of rotor poles should be as small as possible. The minimum number of stator slots is six for a three-phase machine since it should be an even number and also a multiple of three. The number of rotor poles can be 4, 5, 7, 8, etc. Previously, not all of these combinations are suitable for practical use due to issues such as an unbalanced back-electromotive force (EMF) and unbalanced rotor force.

SUMMARY

In an example embodiment, an electric machine includes, but is not limited to, a rotor, a first stator, a second stator, a first plurality of permanent magnets, a second plurality of permanent magnets, a first winding, a second winding, a third winding, and a fourth winding. The rotor includes, but is not limited to, a rotor core having a first face and a second face, a first plurality of poles mounted to extend from the first face, and a second plurality of poles mounted to extend from the second face. The second face faces in a direction opposite to the first face. An aperture is formed through the first face and the second face.

The first stator includes, but is not limited to, a first plurality of core pieces, wherein each core piece of the first plurality of core pieces includes a slot having a first sidewall and a second sidewall. The second stator includes, but is not limited to, a second plurality of core pieces, wherein each core piece of the second plurality of core pieces includes a slot having a first sidewall and a second sidewall. A permanent magnet of the first plurality of permanent magnets is mounted between the first sidewall and the second sidewall of adjacent core pieces of the first plurality of core pieces. A permanent magnet of the second plurality of permanent magnets is mounted between the first sidewall and the second sidewall of adjacent core pieces of the second plurality of core pieces.

The first winding is wound over the first sidewall of a first core piece of the first plurality of core pieces, over a first permanent magnet of the first plurality of permanent magnets mounted between the first sidewall of the first core piece and the second sidewall of a second core piece of the first plurality of core pieces, and over the second sidewall of the second core piece of the first plurality of core pieces, wherein the first core piece and the second core piece of the first plurality of core pieces are adjacent to each other. The second winding is wound over the second sidewall of a third core piece of the first plurality of core pieces, over a second permanent magnet of the first plurality of permanent magnets mounted between the second sidewall of the third core piece and the first sidewall of a fourth core piece of the first plurality of core pieces, and over the first sidewall of the fourth core piece of the first plurality of core pieces, wherein the third core piece and the fourth core piece of the first plurality of core pieces are adjacent to each other. The third winding is wound over the first sidewall of a first core piece of the second plurality of core pieces, over a first permanent magnet of the second plurality of permanent magnets mounted between the first sidewall of the first core piece and the second sidewall of a second core piece of the second plurality of core pieces, and over the second sidewall of the second core piece of the second plurality of core pieces, wherein the first core piece and the second core piece of the second plurality of core pieces are adjacent to each other. The fourth winding is wound over the second sidewall of a third core piece of the second plurality of core pieces, over a second permanent magnet of the second plurality of permanent magnets mounted between the second sidewall of the third core piece and the first sidewall of a fourth core piece of the second plurality of core pieces, and over the first sidewall of the fourth core piece of the second plurality of core pieces, wherein the third core piece and the fourth core piece of the second plurality of core pieces are adjacent to each other. The first winding is closer to the third winding than to the fourth winding.

The first stator is mounted axially relative to the rotor so that a first air gap separates the first plurality of poles from the first winding and the second winding. The second stator is mounted axially relative to the rotor so that a second air gap separates the second plurality of poles from the third winding and the fourth winding. The first permanent magnet of the first plurality of permanent magnets and the second permanent magnet of the first plurality of permanent magnets have opposite polarities. The first permanent magnet of the second plurality of permanent magnets and the second permanent magnet of the second plurality of permanent magnets have opposite polarities. The first winding, the second winding, the third winding, and the fourth winding are connected in series. An absolute value of an angle offset between the first winding and the third winding and between closest poles of the first plurality of poles and the second plurality of poles is 180 electrical degrees.

In another example embodiment, an electric machine includes, but is not limited to, a first rotor, a second rotor, a stator, a plurality of permanent magnets, a first winding, a second winding, a third winding, and a fourth winding. The first rotor includes, but is not limited to, a first rotor core and a first plurality of poles. The first rotor core has a first face and a second face, wherein the second face faces in a direction opposite to the first face. An aperture is formed through the first face and the second face. The first plurality of poles is mounted to extend from the first face of the first rotor core. The second rotor includes, but is not limited to, a second rotor core and a second plurality of poles. The second rotor core has a first face and a second face, wherein the second face faces in a direction opposite to the first face. An aperture is formed through the first face and the second face. The first face of the first rotor core is in a same direction as the first face of the second rotor core. The second plurality of poles is mounted to extend from the second face of the second rotor core.

The stator includes, but is not limited to, a first plurality of core pieces and a second plurality of core pieces. Each core piece of the first plurality of core pieces and of the second plurality of core pieces includes a slot having a first sidewall and a second sidewall. The first plurality of core pieces face towards the first plurality of poles and the second plurality of core pieces face towards the second plurality of poles. A permanent magnet of the plurality of permanent magnets is mounted between the first sidewall and the second sidewall of adjacent core pieces of the first plurality of core pieces and between the first sidewall and the second sidewall of adjacent core pieces of the second plurality of core pieces.

The first winding is wound over the first sidewall of a first core piece of the first plurality of core pieces, over a first permanent magnet of the plurality of permanent magnets mounted between the first sidewall of the first core piece and the second sidewall of a second core piece of the first plurality of core pieces, and over the second sidewall of the second core piece of the first plurality of core pieces, wherein the first core piece and the second core piece of the first plurality of core pieces are adjacent to each other. The second winding is wound over the second sidewall of a third core piece of the first plurality of core pieces, over a second permanent magnet of the plurality of permanent magnets mounted between the second sidewall of the third core piece and the first sidewall of a fourth core piece of the first plurality of core pieces, and over the first sidewall of the fourth core piece of the first plurality of core pieces, wherein the third core piece and the fourth core piece of the first plurality of core pieces are adjacent to each other. The third winding is wound over the first sidewall of a first core piece of the second plurality of core pieces, over the first permanent magnet of the plurality of permanent magnets mounted between the first sidewall of the first core piece and the second sidewall of a second core piece of the second plurality of core pieces, and over the second sidewall of the second core piece of the second plurality of core pieces, wherein the first core piece and the second core piece of the second plurality of core pieces are adjacent to each other. The fourth winding is wound over the second sidewall of a third core piece of the second plurality of core pieces, over the second permanent magnet of the plurality of permanent magnets mounted between the second sidewall of the third core piece and the first sidewall of a fourth core piece of the second plurality of core pieces, and over the first sidewall of the fourth core piece of the second plurality of core pieces, wherein the third core piece and the fourth core piece of the second plurality of core pieces are adjacent to each other. The first winding is closer to the third winding than to the fourth winding;

The stator is mounted axially between the first rotor and the second rotor so that a first air gap separates the first plurality of poles from the first winding and the second winding and a second air gap separates the second plurality of poles from the third winding and the fourth winding. The first permanent magnet of the plurality of permanent magnets and the second permanent magnet of the first plurality of permanent magnets have opposite polarities. The first winding, the second winding, the third winding, and the fourth winding are connected in series. The second plurality of poles is rotated 180 electrical degrees relative to the first plurality of poles.

Other principal features of the disclosed subject matter will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.

DETAILED DESCRIPTION

Referring toFIG. 1, a perspective view of an axial flux switching permanent magnet machine (AFSPM)100is shown in accordance with an illustrative embodiment. AFSPM100may include a rotor102, a left stator104, and a right stator106. In the illustrative embodiment, AFSPM100is a three-phase machine that can be configured as a generator or as a motor as understood by a person of skill in the art. In alternative embodiments, AFSPM100can be configured to support a fewer or a greater number of phases.

Use of directional terms, such as top, bottom, right, left, front, back, upper, lower, horizontal, vertical, behind, etc. are merely intended to facilitate reference to the various surfaces of the described structures relative to the orientations shown in the drawings and are not intended to be limiting in any manner unless otherwise indicated.

AFSPM100may be used in various orientations. A shaft (not shown) may be mounted to extend parallel to a center axis108. Center axis108extends through a center of rotor102, left stator104, and right stator106such that rotor102, left stator104, and right stator106are arranged concentrically around the shaft when AFSPM100is mounted to the shaft.

Rotor102is mounted to the shaft for rotation as understood by a person of skill in the art. Rotor102may be formed of a ferromagnetic material such as lamination steel, iron, cobalt, nickel, etc. as understood by a person of skill in the art. Referring toFIG. 2, rotor102may include a rotor core200, a left plurality of poles, and a right plurality of poles. A number of rotor poles, pr1, of the left plurality of poles equals a number of rotor poles, pr2, of the right plurality of poles. The number of rotor poles may depend on the number of phases supported by AFSPM100. In the illustrative embodiment, pr1=pr2=4, though other numbers of rotor poles are possible. For example, the left plurality of poles may include a first left pole210, a second left pole212, a third left pole214, and a fourth left pole216. The right plurality of poles includes the same number of poles as the left plurality of poles. The right plurality of poles may include a first right pole218, a second right pole220, a third right pole222, and a fourth right pole224.

Rotor core200has a disc shape with an aperture through a center of the disc shape. Rotor core200may include a rotor left face202, a rotor right face204, a rotor exterior face206, and a rotor interior face208. Rotor left face202extends generally perpendicularly from first edges of rotor exterior face206and rotor interior face208. Rotor right face204extends generally perpendicularly from second edges of rotor exterior face206and rotor interior face208. Rotor left face202faces in a direction opposite rotor right face204. Rotor left face202and rotor right face204are generally parallel to each other, flat, and disc-shaped such that the shaft extends through the aperture through a center of the disc shape formed by rotor interior face208.

The left plurality of poles is distributed evenly around rotor left face202, and the right plurality of poles is distributed evenly around rotor right face204. As understood by a person of skill in the art, rotor core200, the left plurality of poles, and the right plurality of poles may be laminations stacked in a radial direction. The laminations may be punched or laser cut.

The left plurality of poles extends generally perpendicularly outward from rotor left face202. The right plurality of poles extends generally perpendicularly outward from rotor right face204. The left and right pluralities of poles extend in alignment from rotor interior face208and from rotor exterior face206. In the illustrative embodiment ofFIG. 2, each pole of the left plurality of poles is aligned with a respective pole of the right plurality of poles. “Aligned with” indicates that each pair of left and right poles extends from the same point around the circumference of rotor102though the left and right poles extend in opposite directions.

The left plurality of poles and the right plurality of poles are distributed at equal angles around the circumference of rotor102. For example, in the illustrative position shown inFIG. 2, first left pole210and first right pole218are positioned at 90 degrees, second left pole212and second right pole220are positioned at 0 degrees, third left pole214and third right pole222are positioned at −90 degrees, and fourth left pole216and fourth right pole224are positioned at 180 degrees relative to a vertical axis236that is perpendicular to center axis108and a third axis238that is perpendicular to both center axis108and vertical axis236.

In the illustrative embodiment, each pole of the left and right pluralities of poles has the same shape and size and is formed of the same material. For illustration, fourth left pole216may include a pole interior face226, a pole bottom face228, a pole exterior face230, a pole upper face232and a stator facing face234. Pole interior face226extends from rotor interior face208. Pole exterior face230extends from rotor exterior face206. Stator facing face234is generally flat and parallel to rotor left face202. Pole bottom face228extends between pole exterior face230and pole interior face226, and pole top face232extends between pole exterior face230and pole interior face226. Fourth left pole216has a truncated pie shape though other polygonal and or elliptical shapes may be used.

The components of rotor102may be integrally formed together or formed of one or more separate pieces that are mounted to each other. As used in this disclosure, the term “mount” further includes join, unite, connect, couple, associate, insert, hang, hold, affix, attach, fasten, bind, paste, secure, bolt, screw, rivet, pin, nail, clasp, clamp, cement, fuse, solder, weld, glue, form over, slide together, layer, and other like terms. The phrases “mounted on” and “mounted to” include any interior or exterior portion of the element referenced. These phrases also encompass direct mounting (in which the referenced elements are in direct contact) and indirect mounting (in which the referenced elements are not in direct contact, but are mounted together via intermediate elements). Elements referenced as mounted to each other herein may further be integrally formed together, for example, using a molding process as understood by a person of skill in the art. As a result, elements described herein as being mounted to each other need not be discrete structural elements. The elements may be mounted permanently, removably, or releasably.

Referring toFIG. 3, left stator104may include a left stator core300, a left plurality of magnets302, and a left plurality of windings304. Right stator106may include a right stator core306, a right plurality of magnets308, and a right plurality of windings310. Left stator104is positioned adjacent the left plurality of poles of rotor102. Right stator106is positioned adjacent the right plurality of poles of rotor102. Left stator104and right stator106have generally circular cross sections with a hollow core sized to accommodate the shaft that rotates rotor102.

Referring again toFIG. 1, left stator104is mounted axially relative to rotor102and a first air gap (not shown) separates the left plurality of poles of rotor102from left stator104. Right stator106is mounted axially relative to rotor102and a second air gap110separates the right plurality of poles of rotor102from right stator106. The first air gap and second air gap110have the same width between the respective poles and stator.

Left stator core300and right stator core306may be formed of laminations stacked in a radial direction. The laminations may be punched or laser cut. Left stator core300and right stator core306may be formed of a ferromagnetic material such as lamination steel, iron, cobalt, nickel, etc. Referring toFIG. 4, left stator core300may include a first plurality of core pieces with two core pieces for each phase. In the illustrative three-phase embodiment, the first plurality of core pieces includes a first left core piece400, a second left core piece402, a third left core piece404, a fourth left core piece406, a fifth left core piece408, and a sixth left core piece410.

Referring toFIG. 5, right stator core306is identical to left stator core300, but flipped 180 degrees relative to a plane defined by vertical axis236and third axis238that is perpendicular to center axis108. Right stator core306may include a second plurality of core pieces, which include a first right core piece500, a second right core piece502, a third right core piece504, a fourth right core piece506, a fifth right core piece508, and a sixth right core piece510.

In the illustrative embodiment, each core piece of the first plurality of core pieces and the second plurality of core pieces has the same size and shape. The first plurality of core pieces and the second plurality of core pieces are arranged around center axis108. In the illustrative embodiment, each core piece has a “C”-shape though an “E”-shape may also be used as understood by a person of skill in the art where the outside edges of the “E”-shape are similar to those described for the “C”-shape. The hollow of the C-shape of each core piece defines a stator slot within which the left plurality of windings304are mounted as described further below. In the illustrative embodiment, the number of stator slots, ps1, of left stator104equals a number of stator slots, ps2, of right stator106. In the illustrative embodiment, ps1=ps2=6, though other numbers of stator slots are possible. The slots are distributed at equal angles around the circumference of left stator104and of right stator106. For example, relative to the plane defined by vertical axis236and third axis238, a center of first left core piece400is positioned at 75 degrees, a center of second first left core piece402is positioned at 15 degrees, a center of third first left core piece404is positioned at −45 degrees, a center of fourth left core piece406is positioned at −105 degrees, a center of fifth left core piece408is positioned at −165 degrees, and a center of sixth left core piece410is positioned at 135 degrees. A center of first right core piece500is positioned at 120 degrees, a center of second first right core piece502is positioned at 60 degrees, a center of third first right core piece504is positioned at 0 degrees, a center of fourth right core piece506is positioned at −60 degrees, a center of fifth right core piece508is positioned at −120 degrees, and a center of sixth right core piece510is positioned at 180 degrees.

Referring again toFIG. 4, second left core piece402may include a left exterior face412, a bottom exterior face414, a bottom, right exterior face416, a bottom, top face418, a right center face420, a top, bottom face422, a top, right exterior face424, a top exterior face426, an exterior circumferential face428, and an interior circumferential face430. The dimensions of the faces of second left core piece402may be relatively wider or narrower than that shown inFIG. 4. Exterior circumferential face428and interior circumferential face430have the C-shape and are curved circumferentially relative to center axis108though exterior circumferential face428and interior circumferential face430may have be flat in other embodiments. Exterior circumferential face428and interior circumferential face430further extend in the direction of the shaft about which AFSPM is mounted. Left exterior face412, bottom, right exterior face416, and top, right exterior face424extend generally parallel to each other and perpendicular to center axis108between exterior circumferential face428and interior circumferential face430.

Bottom exterior face414extends between edges of interior circumferential face430, left exterior face412, exterior circumferential face428, and bottom, right exterior face416. Top exterior face426extends between edges of interior circumferential face430, left exterior face412, exterior circumferential face428, and top, right exterior face424. Bottom, right exterior face416extends between edges of interior circumferential face430, bottom exterior face414, exterior circumferential face428, and bottom, top face418. Top, right exterior face424extends between edges of interior circumferential face430, top exterior face426, exterior circumferential face428, and top, bottom face422. Right center face420extends between edges of interior circumferential face430, bottom, top face418, exterior circumferential face428, and top, bottom face422. Left exterior face412, bottom, right exterior face416, top, right exterior face424, and right center face420are parallel and extend generally perpendicular from exterior circumferential face428and interior circumferential face430. Left exterior face412, bottom, right exterior face416, top, right exterior face424, and right center face420have a truncated pie shape though other polygonal and or elliptical shapes may be used. Bottom, right exterior face416, top, right exterior face424, and right center face420face outwards from left stator core300in an opposite direction to left exterior face412. Bottom, right exterior face416and top, right exterior face424face the left plurality of poles of rotor102when AFSPM100is formed. Bottom exterior face414, bottom, top face418, top, bottom face422, and top exterior face426are generally rectangular.

Referring again toFIG. 5, third right core piece504of right stator core306similarly may include a right exterior face512, a bottom exterior face514, a bottom, left exterior face516, a bottom, top face518, a left center face520, a top, bottom face522, a top, left exterior face524, a top exterior face526, an exterior circumferential face528, and an interior circumferential face530.

Bottom, top face418, right center face420, and top, bottom face422form a slot. Top, bottom face422, top, right exterior face424, and top exterior face426form a first sidewall of the slot formed by each core piece of the first plurality of core pieces. Bottom exterior face414, a bottom, right exterior face416, a bottom, top face418form a second sidewall of the slot formed by each core piece of the first plurality of core pieces.

Bottom, top face518, left center face520, and top, bottom face522form a slot. Top, bottom face522, top, left exterior face524, and top exterior face526form a first sidewall of the slot formed by each core piece of the second plurality of core pieces. Bottom exterior face514, a bottom, left exterior face516, a bottom, top face518form a second sidewall of the slot formed by each core piece of the second plurality of core pieces.

Referring toFIG. 6, the left plurality of magnets302includes two magnets for each phase. In the illustrative three-phase embodiment, the left plurality of magnets302includes a first left magnet600, a second left magnet602, a third left magnet604, a fourth left magnet606, a fifth left magnet608, and a sixth left magnet610. Each magnet of the left plurality of magnets302and the right plurality of magnets308is magnetized to form a south (S) pole on a first side and a north (N) pole on a second side opposite the first side, wherein the magnetization direction is in a radial direction from the first side to the second side of the magnet. The left plurality of magnets302are mounted with N poles adjacent N poles and S poles adjacent S poles to form pole pairs. Thus, first left magnet600, third left magnet604, and fifth left magnet608have an opposite N-S polarity relative to second left magnet602, fourth left magnet606, and sixth left magnet610. For illustration, first left magnet600and second left magnet602form a first pole pair. The pole pairs are formed at a regular pitch circumferentially around left stator104. In the illustrative embodiment, first left magnet600, third left magnet604, and fifth left magnet608have N-S polarity and second left magnet602, fourth left magnet606, and sixth left magnet610have S-N polarity.

First left magnet600, second left magnet602, third left magnet604, fourth left magnet606, fifth left magnet608, and sixth left magnet610have a truncated pie shape that is sized to fit in slots formed between adjacent core pieces of the first plurality of core pieces. First left magnet600, second left magnet602, third left magnet604, fourth left magnet606, fifth left magnet608, and sixth left magnet610may have other polygonal and or elliptical shapes in alternative embodiments. For example, second left magnet602is mounted in a slot formed between first left core piece400and second left core piece402, more specifically between top exterior face426of second left core piece402and bottom exterior face414of first left core piece400. Similarly, third left magnet604is mounted in a slot formed between second left core piece402and third left core piece404; fourth left magnet606is mounted in a slot formed between third left core piece404and fourth left core piece406; fifth left magnet608is mounted in a slot formed between fourth left core piece406and fifth left core piece408; sixth left magnet610is mounted in a slot formed between fifth left core piece408and sixth left core piece410; and first left magnet600is mounted in a slot formed between sixth left core piece410and first left core piece400. For example, relative to the plane defined by vertical axis236and third axis238, a center of first left magnet600is positioned at 105 degrees, a center of second left magnet602is positioned at 45 degrees, a center of third left magnet604is positioned at −15 degrees, a center of fourth left magnet606is positioned at −75 degrees, a center of fifth left magnet608is positioned at −135 degrees, and a center of sixth left magnet610is positioned at 165 degrees.

Similarly, referring toFIG. 7, the right plurality of magnets308includes two magnets for each phase. In the illustrative three-phase embodiment, the right plurality of magnets308includes a first right magnet700, a second right magnet702, a third right magnet704, a fourth right magnet706, a fifth right magnet708, and a sixth right magnet710. The right plurality of magnets308are mounted with N poles adjacent N poles and S poles adjacent S poles to form pole pairs. Thus, first right magnet700, third right magnet704, and fifth right magnet708have an opposite N-S polarity relative to second right magnet702, fourth right magnet706, and sixth right magnet710. For illustration, first right magnet700and second right magnet702form a first pole pair. The pole pairs are formed at a regular pitch circumferentially around right stator106. In the illustrative embodiment, first right magnet700, third right magnet704, and fifth right magnet708have S-N or opposite N-S polarity and second right magnet702, fourth right magnet706, and sixth right magnet710have N-S polarity.

First right magnet700, second right magnet702, third right magnet704, fourth right magnet706, fifth right magnet708, and sixth right magnet710have a truncated pie shape that is sized to fit between adjacent core pieces of the second plurality of core pieces. First right magnet700, second right magnet702, third right magnet704, fourth right magnet706, fifth right magnet708, and sixth right magnet710may have other polygonal and or elliptical shapes in alternative embodiments. For example, second right magnet702is mounted in a slot formed between second right core piece502and third right core piece504, more specifically between top exterior face526of third right core piece504and bottom exterior face514of second right core piece502. Similarly, third right magnet704is mounted in a slot formed between third right core piece504and fourth right core piece506; fourth right magnet706is mounted in a slot formed between fourth right core piece506and fifth right core piece508; fifth right magnet708is mounted in a slot formed between fifth right core piece508and sixth right core piece510; sixth right magnet710is mounted in a slot formed between sixth right core piece510and first right core piece500; and first right magnet700is mounted in a slot formed between first right core piece500and second right core piece502. For example, relative to the plane defined by vertical axis236and third axis238, a center of first right magnet700is positioned at 90 degrees, a center of second right magnet702is positioned at 30 degrees, a center of third right magnet704is positioned at −30 degrees, a center of fourth right magnet706is positioned at −90 degrees, a center of fifth right magnet708is positioned at −150 degrees, and a center of sixth right magnet710is positioned at 150 degrees.

In the arrangement shown in the illustrative embodiment ofFIG. 1, first left magnet600has an opposite N-S polarity relative to first right magnet700. The left plurality of magnets302and the right plurality of magnets308are permanent magnets that may be formed of rare earth magnets, such as neodymium and dysprosium, of ferrite based magnets, etc. The left plurality of magnets302and the right plurality of magnets308are electrically isolated from each other. First left magnet600may have the same N-S polarity relative to first right magnet700if current direction on the right plurality of windings310is reversed relative to that shown inFIG. 12.

Referring toFIG. 8, the left plurality of windings304includes two windings for each phase. In the illustrative embodiment, each winding of the left plurality of windings304is trapezoidal and concentrated though other winding configurations may be used. In the illustrative three-phase embodiment, the left plurality of windings304includes a first left winding800, a second left winding802, a third left winding804, a fourth left winding806, a fifth left winding808, and a sixth left winding810. First left winding800and fourth left winding806are connected to receive a second phase. Second left winding802and fifth left winding808are connected to receive a third phase. Third left winding804and sixth left winding810are connected to receive a first phase. The first phase, the second phase, and the third phase are separated by 360/N or 120 degrees in the illustrative three-phase embodiment, where N is the number of phases. The first phase may be denoted as an “A”-phase; the second phase may be denoted as a “B”-phase; and the third phase may be denoted as a “C”-phase.

The left plurality of windings304mount through the slot formed by the hollow part of the C-shape of two adjacent core pieces such that each winding extends over a different magnet of the left plurality of magnets302. As an example, second left winding802is wound over a bottom portion of interior circumferential face430, over bottom, top face418, and over a bottom portion of exterior circumferential face428of first core piece400, over an exterior facing side of second left magnet602, over a top portion of exterior circumferential face428, over top, bottom face422, and over a top portion of interior circumferential face430of second core piece402, and over an interior facing side of second left magnet602. Thus, second left winding802is wound over the second sidewall of the slot formed by first core piece400, over second left magnet602, and over the first sidewall of the slot formed by second core piece402.

Each additional winding is similarly wound around respective core pieces and magnets. For example, third left winding804is similarly wound over second core piece402, third left magnet604, and third core piece404; fourth left winding806is similarly wound over third core piece404, fourth left magnet606, and fourth core piece406; fifth left winding808is similarly wound over fourth core piece406, fifth left magnet608, and fifth core piece408; sixth left winding810is similarly wound over fifth core piece408, sixth left magnet610, and sixth core piece410; and first left winding800is similarly wound over sixth core piece410, first left magnet600, and first core piece400.

Referring toFIG. 9, similar to the left plurality of windings302, the right plurality of windings310includes two windings for each phase where each winding is trapezoidal and concentrated. In the illustrative three-phase embodiment, the right plurality of windings310includes a first right winding900, a second right winding902, a third right winding904, a fourth right winding906, a fifth right winding908, and a sixth right winding910. In the illustrative embodiment, first right winding900and fourth right winding906are connected to receive the third phase; second right winding902and fifth right winding908are connected to receive the first phase; and third right winding904and sixth right winding910are connected to receive the second phase.

The right plurality of windings310mount through the slot formed by the hollow part of the C-shape of two adjacent core pieces such that each winding extends over a different magnet of the right plurality of magnets308. As an example, second right winding902is wound over a bottom portion of interior circumferential face530, over bottom, top face518, and over a bottom portion of exterior circumferential face528of second core piece502, over an exterior facing side of second right magnet702, over a top portion of exterior circumferential face528, over top, bottom face522, and over a top portion of interior circumferential face530of third core piece504, and over an interior facing side of second right magnet702. Thus, second right winding902is wound over the second sidewall of the slot formed by second core piece502, over second right magnet702, and over the first sidewall of the slot formed by third core piece504.

Each additional winding is similarly wound over respective core pieces and magnets. For example, third right winding904is similarly wound over third core piece504, third right magnet704, and fourth core piece506; fourth right winding906is similarly wound over fourth core piece506, fourth right magnet706, and fifth core piece508; fifth right winding908is similarly wound over fifth core piece508, fifth right magnet708, and sixth core piece510; sixth right winding910is similarly wound over sixth core piece510, sixth right magnet710, and first core piece500; and first right winding900is similarly wound over first core piece500, first right magnet700, and second core piece502.

Referring again toFIG. 1, an insulation gap112may separate the left plurality of windings304from the first plurality of core pieces of left stator104. Insulation may be mounted within insulation gap112. Similar insulation gaps may be formed between each winding of the left plurality of windings304and respective core pieces of the first plurality of core pieces of left stator104. Similarly, insulation gaps may be formed between each winding of the right plurality of windings310and respective core pieces of the second plurality of core pieces of right stator106.

Referring toFIG. 10, a right to left view of left stator104is shown in accordance with an illustrative embodiment. For illustration, a N-S polarity is indicated for each magnet of the left plurality of magnets302. For illustration, an arrow also shows a direction of positive current in each winding of the left plurality of windings304. Referring toFIG. 11, a left to right view of right stator106is shown in accordance with an illustrative embodiment. For illustration, a N-S polarity is indicated for each magnet of the right plurality of magnets308. For illustration, an arrow also shows a direction of positive current in each winding of the right plurality of windings310.

In the illustrative embodiment, AFSPM100includes three-phase windings that are tied together. For example, referring toFIG. 12, in an illustrative embodiment, the left plurality of windings304and the right plurality of windings310are tied together at a central connection point1208to form a “Y” configuration. Sixth left winding810is connected between a first connection point1200and a second connection point1202. Third left winding804is connected between second connection point1202and a third connection point1204. Second right winding902is connected between third connection point1204and a fourth connection point1206. Fifth right winding908is connected between fourth connection point1206and central connection point1202. Thus, sixth left winding810, third left winding804, second right winding902, and fifth right winding908are connected in series between first connection point1200and central connection point1208, where the “+” indicates positive current flow with the first phase from first connection point1200to central connection point1208such that each of sixth left winding810, third left winding804, second right winding902, and fifth right winding908can be referred to as a positive winding.

Fourth left winding806is connected between a fifth connection point1210and a sixth connection point1212. First left winding800is connected between sixth connection point1212and a seventh connection point1214. Third right winding904is connected between seventh connection point1214and an eighth connection point1216. Sixth right winding910is connected between eighth connection point1216and central connection point1208. Thus, fourth left winding806, first left winding800, third right winding904, and sixth right winding910are connected in series between fifth connection point1210and central connection point1208, where the “+” indicates positive current flow with the second phase from fifth connection point1210to central connection point1202such that each of fourth left winding806, first left winding800, third right winding904, and sixth right winding910can be referred to as a positive winding.

Second left winding802is connected between a ninth connection point1218and a tenth connection point1220. Fifth left winding808is connected between tenth connection point1220and an eleventh connection point1222. First right winding900is connected between eleventh connection point1222and a twelfth connection point1224. Fourth right winding906is connected between twelfth connection point1224and central connection point1208. Thus, second left winding802, fifth left winding808, first right winding900, and fourth right winding906are connected in series between ninth connection point1218and central connection point1202, where the “+” indicates positive current flow with the third phase from ninth connection point1218to central connection point1208such that each of second left winding802, fifth left winding808, first right winding900, and fourth right winding906can be referred to as a positive winding.

Referring toFIG. 13, a perspective view of AFSPM100is shown again in accordance with an illustrative embodiment illustrating angles between the poles of rotor102and between the windings of left stator104and right stator106. As stated previously, the left plurality of poles and the right plurality of poles of rotor102of AFSPM100are aligned so that a rotor angle θr=0 in mechanical and electrical degrees. Third left winding804and second right winding902are offset by a stator angle1300of 45 mechanical degrees resulting in a stator shift θsof 180 electrical degrees or π electrical radians because θmech=θelec/pr1. Thus, an angular offset θoff=|θs−θr|=|π−0|=π exists between the left and right plurality and poles of rotor102and the windings of left stator104and right stator106.

Referring toFIG. 14, a perspective view of a second AFSPM1400is shown in accordance with a second illustrative embodiment. Second AFSPM1400may include a second rotor102a, left stator104, and right stator106. In the illustrative embodiment, second AFSPM1400is a three-phase machine that can be configured as a generator or as a motor as understood by a person of skill in the art. In alternative embodiments, second AFSPM1400can be configured to support a fewer or a greater number of phases.

Second rotor102ais identical to rotor102except that the right plurality of poles are rotated a rotor angle1402equal to 45 mechanical degrees or 180 electrical degrees relative to the left plurality of poles.

In comparison with AFSPM100, right stator106of second AFSPM1400has also been rotated relative to left stator104. Relative to the plane defined by vertical axis236and third axis238, a center of first right core piece500is positioned at 75 degrees, a center of second first right core piece502is positioned at 15 degrees, a center of third first right core piece504is positioned at −45 degrees, a center of fourth right core piece506is positioned at −105 degrees, a center of fifth right core piece508is positioned at −165 degrees, and a center of sixth right core piece510is positioned at 135 degrees. Thus, right stator106of second AFSPM1400is rotated 45 mechanical degrees relative to right stator106of AFSPM100.

Thus, for second AFSPM1400, stator angle θs=0 and a rotor angle θrequals 180 electrical degrees or π electrical radians. Thus, the angular offset is θoff=|θs−θr|=|0−π|=π.

Referring toFIG. 15, a perspective view of a third AFSPM1500is shown in accordance with a second illustrative embodiment. Third AFSPM1500may include a third rotor102b, left stator104, and right stator106. In the illustrative embodiment, third AFSPM1500is a three-phase machine that can be configured as a generator or as a motor as understood by a person of skill in the art. In alternative embodiments, third AFSPM1500can be configured to support a fewer or a greater number of phases.

Third rotor102bis identical to rotor102except that the right plurality of poles are rotated a second rotor angle1500relative to the left plurality of poles and, relative to AFSPM100, right stator106of third AFSPM1500has been rotated a second stator angle1502such that the angular offset remains θoff=|θs−θr|=π in electrical degrees. The left half of third AFSPM1500that includes left stator104and the left plurality of poles of third rotor102band the right half of third AFSPM1500that includes right stator106and the right plurality of poles of third rotor102bcan operate separately so that the left half and the right half can be shifted to any degree as long as the relationship θoff=|θs−θr|=π is maintained. In the illustrative example, rotor angle1402is 15 mechanical degrees or 60 electrical degrees and stator angle1300is 60 mechanical degrees or 240 electrical degrees.

Each of AFSPM100, second AFSPM1400, and third AFSPM1500eliminate even order harmonic components of flux linkage. In a dual stator, single rotor AFSPM machine, a second flux linkage component is introduced because of an additional linkage between the second (right) stator and rotor102. The total flux linkage can be defined as:
λa≈Λ1sin(prθm)+Λ2sin(2prθm)+(−1)kΛ1sin(prθm+θoff)+(−1)kΛ2sin(2prθm+2θoff)
where pris the number of rotor poles of the left plurality of poles and of the right plurality of poles of rotor102,102a,102b. θoffas described above is the electrical offset angle between the two flux linkages in radians and θmis the mechanical position of rotor102, second rotor102a, or third rotor102b.

The total flux linkage becomes:

Referring toFIG. 16, θoff=π is shown in accordance with an illustrative embodiment of AFSPM100, second AFSPM1400, or third AFSPM1500. A first curve1600shows a fundamental flux linkage from left stator104. A second curve1602shows a second harmonic of flux linkage from left stator104. A third curve1604shows a fundamental flux linkage from right stator106. A fourth curve1606shows a second harmonic of flux linkage from right stator106. A fifth curve1608shows a total flux linkage from left stator104and from right stator106. Second curve1602and fourth curve1606sum to zero indicating that the second order harmonic component of flux linkage is effectively eliminated. First curve1600and third curve1604are in phase resulting in a total flux linkage that is doubled at the fundamental frequency. p.u. stands for per unit. A per-unit system is an expression of system quantities as fractions of a defined base unit quantity. Here, the peak value of the fundamental flux linkage defined the base unit quantity so that their peaks become one.

The various dimensions of the elements of rotor102, second rotor102a, third rotor102b, left stator104, and right stator106, including the first air gap and the second air gap110, may be determined based on desired rated performance characteristics using analytical sizing equations and finite element analysis using an electromechanical design tool.

The performance of AFSPM100, second AFSPM1400, and third AFSPM1500was evaluated using finite element analysis. A design specification of AFSPM100, second AFSPM1400, and third AFSPM1500is summarized in Table I below.

TABLE ICALCULATED MACHINE DIMENSIONSSymbolQuantitySizeDoOuter diameter350 mmDiInner diameter114 mmIcrRotor core thickness29 mmIcsStator yoke thickness58 mmIstStator tooth thickness84 mmhpmMagnet height84 mm
where Diis an inner diameter and Dois an outer diameter of rotor102,102a,102band of left stator core300, the left plurality of magnets302, right stator core306, and the right plurality of magnets308, and the stator yoke thickness is a thickness of bottom exterior face414, top exterior face426, bottom exterior face514, and top exterior face526.

FIG. 17shows Fourier transform analysis results calculated for the back-EMF waveforms generated by AFSPM100with θoff=π. A first curve1700shows a fundamental back-EMF value from left stator104. A second curve1702shows a fundamental back-EMF from right stator106. A third curve1704shows a total fundamental back-EMF from left stator104and from right stator106. A fourth curve1706shows a second harmonic of back-EMF from left stator104. A fifth curve1708shows a second harmonic of back-EMF from right stator106. A sixth curve1710shows a total second harmonic of back-EMF from left stator104and from right stator106. The total fundamental harmonic is 148 Volts (V). The total second order harmonic is 0.233 V, which is a 99.8% cancellation compare to a conventional dual stator topology.

FIG. 18shows a comparison between the flux linkage generated by AFSPM100, second AFSPM1400, and third AFSPM1500, with θoff=π. A first curve1800shows a total fundamental flux linkage value from left stator104and from right stator106of AFSPM100. A second curve1802shows a total fundamental flux linkage value from left stator104and from right stator106of second AFSPM1400. A third curve1804shows a total fundamental flux linkage value from left stator104and from right stator106of third AFSPM1500. A fourth curve1806shows a total second harmonic of flux linkage from left stator104and from right stator106of AFSPM100. A fifth curve1808shows a total second harmonic of flux linkage from left stator104and from right stator106of second AFSPM1400. A sixth curve1810shows a total second harmonic of flux linkage from left stator104and from right stator106of third AFSPM1500. AFSPM100produced a total fundamental flux linkage of 0.98 Weber (wb), while second AFSPM1400and third AFSPM1500produced 0.916 wb and 0.905 wb respectively. AFSPM100produced 6.98% and 8.28% larger total fundamental flux linkage than that of the second AFSPM1400and third AFSPM1500. The total second order harmonics of AFSPM100, second AFSPM1400, and third AFSPM1500were 0.0004 wb, 0.011 wb, and 0.005 wb. Second AFSPM1400had 97.42% of remaining second order harmonic, while AFSPM100and third AFSPM1500had 99.8% and 98.73% respectively.

FIG. 19shows a comparison between the back-EMF generated by AFSPM100, second AFSPM1400, and third AFSPM1500, with θoff=π. A first curve1900shows a total fundamental back-EMF value from left stator104and from right stator106of AFSPM100. A second curve1902shows a total fundamental back-EMF value from left stator104and from right stator106of second AFSPM1400. A third curve1904shows a total fundamental back-EMF value from left stator104and from right stator106of third AFSPM1500. A fourth curve1906shows a total second harmonic of back-EMF from left stator104and from right stator106of AFSPM100. A fifth curve1908shows a total second harmonic of back-EMF from left stator104and from right stator106of second AFSPM1400. A sixth curve1910shows a total second harmonic of back-EMF from left stator104and from right stator106of third AFSPM1500.

The analytical calculations were performed under the assumption that left stator104and right stator106of AFSPM100, of second AFSPM1400, and of third AFSPM1500were symmetrical and identical.

Instead of using a dual stator configuration, a dual rotor configuration also achieves the balanced flux linkage and back-EMF waveforms as discussed relative to AFSPM100, second AFSPM1400, and third AFSPM1500. Referring toFIG. 20, a perspective view of a fourth AFSPM2000is shown in accordance with an illustrative embodiment. Fourth AFSPM2000may include a left rotor102c, a right rotor102d, and a stator2002. In the illustrative embodiment, fourth AFSPM2000is a three-phase machine that can be configured as a generator or as a motor as understood by a person of skill in the art. In alternative embodiments, fourth AFSPM2000can be configured to support a fewer or a greater number of phases. Fourth AFSPM2000is essentially a rearrangement of the elements of second AFSPM1400.

Left rotor102cmay be formed as a first half of second rotor102athat includes half of rotor core200and the right plurality of poles. Right rotor102dmay be formed as a second half of second rotor102athat includes a remaining half of rotor core200and the left plurality of poles. Left rotor102cis mounted axially on a left side of stator2002and right rotor102dis mounted axially on a right side of stator2002. The first air gap separates stator2002from left rotor102cand second air gap110(not visible) separates stator2002from right rotor102d.

Stator2002is similar to left stator104and right stator106mounted together to form a single stator positioned axially between left rotor102cand right rotor102d. Stator2002may include a stator core2004, a plurality of magnets2006, the left plurality of windings304, and the right plurality of windings310. Stator core2004may include left stator core300and right stator core306. Left exterior face412of each of the first plurality of core pieces of left stator core300is mounted to right exterior face512of the second plurality of core pieces of right stator core306to form stator2002.

The left plurality of windings304are mounted to the first plurality of core pieces of left stator core300that forms a right half of stator2002. Second air gap110separates the left plurality of poles of right rotor102dfrom the left plurality of windings304. The right plurality of windings310are mounted to the second plurality of core pieces of right stator core306that forms a left half of stator2002. The first air gap separates the right plurality of poles of left rotor102cfrom the right plurality of windings310. Third left winding804is aligned with second right winding902in the plane defined by vertical axis236and third axis238. Similarly, fourth left winding806is aligned with third right winding904; fifth left winding808is aligned with fourth right winding906; sixth left winding810is aligned with fifth right winding908; first left winding800is aligned with sixth right winding910; and second left winding802is aligned with first right winding900. The left plurality of windings304and the right plurality of windings310are connected as shown inFIG. 12.

The plurality of magnets2006is similar to the left plurality of magnets302and to the right plurality of magnets308. The plurality of magnets2006are mounted between adjacent core pieces of stator core2004with alternating N-S polarity as described with reference to AFSPM100.

Similar to second AFSPM1400, left rotor102cand right rotor102dare shifted by 45 mechanical degrees resulting in 180 electric degrees shift based on the alignment between the left plurality of windings304and the right plurality of windings310, which compensate each other as described with reference to second AFSPM1400. As a result, the coil flux linkages add up to form a waveform that is very close to sinusoidal so that the three phase back-EMFs are balanced. Fourth AFSPM2000then achieves a similar performance to that described for AFSPM100, second AFSPM1400, and third AFSPM1500.

AFSPM100, second AFSPM1400, third AFSPM1500, and fourth AFSPM2000use a low number of rotor poles that is amenable particularly for high-speed operation though AFSPM100, second AFSPM1400, third AFSPM1500, and fourth AFSPM2000can be used for medium and low speed applications. AFSPM100, second AFSPM1400, third AFSPM1500, and fourth AFSPM2000also reduce core losses, copper losses, and inverter switching losses thereby increasing the efficiency and power density. Axial flux machines can be used in many applications including heating, ventilation, and air conditioning systems, industrial systems, flywheels, fans, pumps, traction drives for hybrid and electric vehicles, aircraft and marine applications, etc. AFSPM100, second AFSPM1400, third AFSPM1500, and fourth AFSPM2000can be cascaded.

The word “illustrative” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “illustrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more”. Still further, in the detailed description, using “and” or “or” is intended to include “and/or” unless specifically indicated otherwise.

The foregoing description of illustrative embodiments of the disclosed subject matter has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the disclosed subject matter to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed subject matter. The embodiments were chosen and described in order to explain the principles of the disclosed subject matter and as practical applications of the disclosed subject matter to enable one skilled in the art to utilize the disclosed subject matter in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the disclosed subject matter be defined by the claims appended hereto and their equivalents.