Axial flux electrical machine
A stator ( 10 ) for an axial flux electrical machine ( 100 ), an axial flux machine ( 100 ) that includes the stator ( 10 ), and a method ( 500 ) of manufacturing a stator ( 10 ) are provided. The conductive coils ( 12 ) which form the stator ( 10 ) provide a structure which includes spaces ( 131 a, 131 b, 131 c, 132 a, 132 b ) for flux guides ( 30 ), which improves ease of stator manufacture. It also allows for a high number of slots per pole per phase, which provides a more sinusoidal back-EMF. The stator ( 10 ) comprises a plurality of circumferentially distributed conductive coils ( 12 ), each of the plurality of conductive coils configured to be connected to a phase of a multi-phase power supply and comprising at least one pair of active sections ( 121 a, 121 b ), wherein each active section ( 121 a, 121 b ) extends in a generally radial direction substantially perpendicular to an axis of rotation of the electrical machine ( 100 ), wherein the generally radially extending active sections ( 121 a, 121 b ) of each pair are pitched apart in a circumferential direction, and wherein circumferentially adjacent conductive coils ( 12 ) circumferentially overlap to define a space of a first type ( 131 a, 131 b, 131 c ) for receiving a flux guide ( 30 ), each space of the first type ( 131 a, 131 b, 131 c ) being a circumferential space between two adjacent active sections of two different coils.
1. A stator for an axial flux electrical machine, the stator comprising a plurality of circumferentially distributed conductive coils, each of the plurality of conductive coils configured to be connected to a phase of a multi-phase power supply and comprising at least one pair of active sections, wherein each active section extends in a generally radial direction substantially perpendicular to an axis of rotation of the electrical machine, wherein the generally radially extending active sections of each pair are pitched apart in a circumferential direction, and wherein circumferentially adjacent conductive coils circumferentially overlap to define spaces of a first type for receiving a flux guide, each space of the first type being a circumferential space between two adjacent active sections of two different coils, wherein each conductive coil comprises a plurality of pairs of active sections connected to each other in series, and wherein adjacent pairs of active sections circumferentially overlap so as to define a space of a second type for receiving a flux guide, the space of the second type being a circumferential space between two adjacent active sections of the same coil but different pairs of active sections of the coil.
2. The stator of claim 1 , wherein, in use, current flows in opposite radial directions along the active sections of each pair of active sections of each coil.
3. The stator of claim 1 , wherein the number of pairs of active sections of each coil is an integer multiple of two.
4. The stator of claim 1 , wherein the plurality of pairs of active sections of each coil are either integrally formed or formed by connecting, in series, a plurality of separate elements which each comprise one pair of active sections.
5. The stator of claim 1 , further comprising flux guides positioned in the first and/or second types of spaces.
6. The stator of claim 1 , wherein the plurality of conductive coils are provided in a plurality of groups, each group corresponding to one pole of the stator.
7. The stator of claim 1 , wherein circumferentially adjacent conductive coils are configured to be connected to different phases of the multi-phase supply such that, for an N-phase power supply, the stator comprises a plurality of groups of N conductive coils, each group of N conductive coils comprising one coil for each phase of the N-phase supply, each group corresponding to one pole of the stator.
8. The stator of claim 1 , configured so that, in use, current flows in the same direction along adjacent active sections separated by one of the spaces of the second type for a flux guide.
9. The stator of claim 1 , wherein the active sections of each pair of active sections are axially offset from each other.
10. The stator of claim 1 , wherein each active section comprises a plurality of circumferentially stacked winding turning portions.
11. The stator of claim 1 , wherein, for each phase of the multi-phase power supply, every second coil of the stator that is connected to said phase is connected to a common busbar.
12. A yokeless axial flux electrical machine comprising the stator of claim 1 .
13. A stator for an axial flux electrical machine, the stator-comprising a plurality of circumferentially distributed conductive coils, each of the plurality of conductive coils configured to be connected to a phase of a multi-phase power supply and comprising at least one pair of active sections, wherein each active section extends in a generally radial direction substantially perpendicular to an axis of rotation of the electrical machine, wherein the generally radially extending active sections of each pair are pitched apart in a circumferential direction, and wherein circumferentially adjacent conductive coils circumferentially overlap to define spaces of a first type for receiving a flux guide, each space of the first type being a circumferential space between two adjacent active sections of two different coils, wherein each active section comprises a plurality of winding turn portions stacked parallel to the axis of rotation such that a cross-section perpendicular to the radial direction of each active section is elongate with a major dimension parallel to the axis of rotation.
14. The stator of claim 13 , wherein the winding turn portions of the first and second generally radially extending active sections have proximal ends located at an inner radius and distal ends located at an outer radius, and wherein the proximal ends of the winding turn portions are connected by inner loop sections and the distal ends are connected by outer loop sections such that, in use, current flows in opposite radial directions along the pair of radially extending active sections.
15. The stator of claim 14 , wherein the outer loop sections are configured to form an outer part of the coil that is substantially parallel to the axis of rotation, and/or the inner loop sections are configured to form an inner part of the coil that is substantially parallel to the axis of rotation.
16. The stator of claim 15 , wherein each outer loop section comprises a substantially semi-circular or rectangular section such that the outer part of the coil is a half-disk or rectangular surface.
17. The stator of claim 15 , further comprising a stator housing that comprises circumferentially distributed and axially extending apertures for receiving the outer parts of the conductive coils that are substantially parallel to the axis of rotation.
18. The stator of claim 14 , wherein the outer loop sections are configured to form a substantially involute portion, and/or the inner loop sections are configured to form a substantially involute section of the coil.
19. The stator of claim 13 , wherein each conductive coil comprises a plurality of pairs of active sections connected to each other in series, and wherein adjacent pairs of active sections circumferentially overlap so as to define a space of a second type for receiving a flux guide, the space of the second type being a circumferential space between two adjacent active sections of the same coil but different pairs of active sections of the coil.
20. A method of manufacturing a stator of an axial flux electrical machine, comprising:
positioning a plurality of conductive coils in a stator housing so that the plurality of coils are circumferentially distributed around the stator housing, wherein conductive coils are positioned so that circumferentially adjacent conductive coils circumferentially overlap and thereby define spaces of a first type receiving a flux guide, the space of the first type being a circumferential space in the region where two coils overlap, and each conductive coil comprises a plurality of pairs of active sections connected to each other in series, wherein adjacent pairs of active sections circumferentially overlap so as to define a space of a second type for receiving a flux guide, the space of the second type being a circumferential space between two adjacent active sections of the same coil but different pairs of active sections of the coil; and
positioning flux guides in the spaces of the first type.