GB2595933A

GB2595933A - Electric machine apparatus

Info

Publication number: GB2595933A
Application number: GB2008972.8A
Authority: GB
Inventors: Michaelides Alexandros; Christopher Thackwell Cleef; Kiraly Istvan
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2020-06-12
Filing date: 2020-06-12
Publication date: 2021-12-15
Also published as: WO2021250259A1; GB202008972D0

Abstract

A stator 4 for an electric machine 2, the stator comprising a cylindrical core 12 comprising slots 13-n, where each of the slots extend in a radial direction R. At least one first conductor 14-n is disposed in each slot, having a first radial dimension RD1 in the radial direction, and at least one second conductor 15-n is disposed in each slot having a second radial dimension RD2, where the first radial dimension is less than the second radial dimension. The first conductor may be disposed in a radially inner region of each slot and the second conductor disposed in a radially outer region of each slot. Each slot may comprise two of the first conductors for each second conductor. The first radial dimension may be approximately half of the second radial dimension. The conductors may be formed by a leg portion of a U-shaped conductor. The first and second conductors may have the same length in a longitudinal direction. The conductors may be arranged in subsets and sub-assemblies in order to connect them in a number of different winding and phase configurations to inverters that control the machine. The machine may be used in a vehicle.

Description

ELECTRIC MACHINE APPARATUS

TECHNICAL FIELD

The present disclosure relates to electric machine apparatus. Aspects of the invention relate to a stator for an electric machine; an electric machine; and a vehicle comprising an electric machine.

BACKGROUND

It is known to utilise one or more electrical machine in a vehicle to generate a tractive force to propel the vehicle. The vehicle may be a road vehicle, such as an automobile. The electrical machines may be used in a Hybrid Electrical Vehicle (HEV), a Plug-in Hybrid Electrical Vehicle (PHEV) where an internal combustion engine can be non-operational (EV mode); or a Battery Electrical Vehicle (BEV) in which there is no internal combustion engine. To reduce packaging requirements, it is desirable to provide a high torque and power density. One frequently used solution for volume reduction is the more efficient usage of volume in the stator slots, where the conductors are placed. This space saving can be implemented by using isolated rectangular sloid conductors which results in significantly higher slot fill factor (copper volume/slot volume >60%) than at the traditional round wire conductors (<50%). These rectangular conductors form a hairpin winding.

When these rectangular solid conductors are in the pulsating magnetic field, eddy currents occur in the solid conductors. The planes determined by the eddy current are perpendicular to the magnetic flux lines, and their values increases by flux density and the frequency of the pulsating field. These eddy currents generate significant heat in the conductors, despite that these circulating currents do not develop any useful moment on the machine shaft, so the reduction of these parasitic currents improve the efficiency of electrical motors.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a stator for an electric machine; an electric machine; and a vehicle as claimed in the appended claims.

According to an aspect of the present invention there is provided a stator for an electric machine, the stator comprising: a cylindrical stator core comprising a plurality of slots, each of the slots extending in a substantially radial direction; at least one first conductor disposed in each slot, the or each first conductor having a first radial dimension in the substantially radial direction; and at least one second conductor disposed in each slot, the or each second conductor has a second radial dimension in the substantially radial direction; wherein the first radial dimension is less than the second radial dimension.

By configuring the stator such that the first radial dimension of the first conductor is less than the second radial dimension of the second conductor, the area of the surface perpendicular to the magnetic flux lines in the stator may be reduced. The electrical field which develops the eddy currents may be lower than prior art arrangements. Alternatively, or in addition, the components of induced voltage responsible for generating eddy currents may be lower. Accordingly, eddy current losses in the first conductors and/or the second conductors may be reduced. The smaller cross section of the first conductors may reduce the alternating current (AC) losses generated by eddy currents. The first radial dimension represents an extent of the or each first conductor in the substantially radial direction; and the second radial dimension represents an extent of the or each second conductor in the substantially radial direction.

The or each first conductor may be electrically insulated. An exterior of the or each first conductor may be electrically insulated. The or each first conductor may comprise a first outer insulator. The first outer insulator may comprise a film, a yarn, a tape or an extruded compound (or polymer).

The or each second conductor may be insulated. An exterior of the or each second conductor may be electrically insulated. The or each second conductor may comprise a second outer insulator. The second outer insulator may comprise a film, a yarn, a tape or an extruded compound (or polymer).

The at least one first conductor may be in the form of a first formed conductor. The or each first formed conductor may be formed prior to insertion into the stator core, for example for axial insertion into the stator core. The or each first conductor may comprise or consist of a first electrically conductive element.

The at least one second conductor may be in the form of a second formed conductor. The or each second formed conductor may be formed prior to insertion into the stator core, for example for axial insertion into the stator core. The or each second conductor may comprise or consist of a first electrically conductive element.

The at least one first conductor may comprise or consist of a first electrically conductive wire. The first electrically conductive wire may have a single core. The first electrically conductive wire may have a single strand (rather than a plurality of strands or filaments). The first electrically conductive wire may be a solid wire. The first electrically conductive wire may comprise an outer electrical insulation. The first electrically conductive wire may have a circular cross-section. Alternatively, the first electrically conductive wire may have an elliptical cross-section or a rectangular cross-section.

Alternatively, the first electrically conductive wire may comprise a plurality of strands (or filaments). The first electrically conductive wire may, for example, comprise a plurality of film-insulated strands. The strands may, for example, be twisted or braided. The strands may be compressed or compacted, for example into a rectangular profile. The first electrically conductive wire may comprise a Litz wire, for example a twisted, braided or compacted Litz wire.

The at least one second conductor may comprise or consist of a second electrically conductive wire. The second electrically conductive wire may have a single core. The second electrically conductive wire may have a single strand (rather than a plurality of strands or filaments). The second electrically conductive wire may be a solid wire. The second electrically conductive wire may comprise an outer electrical insulation. The second electrically conductive wire may have a circular cross-section. Alternatively, the second electrically conductive wire may have an elliptical cross-section or a rectangular cross-section.

Alternatively, the second electrically conductive wire may comprise a plurality of strands (or filaments). The second electrically conductive wire may, for example, comprise a plurality of film-insulated strands. The strands may, for example, be twisted or braided. The strands may be compressed or compacted, for example into a rectangular profile. The second electrically conductive wire may comprise a Litz wire, for example a twisted, braided or compacted Litz wire.

The stator core may comprise a plurality of stator teeth. The or each first conductor and/or the or each second conductor may be wound around the stator teeth. The or each first conductor may be axially or radially inserted in the stator core. The or each second conductor may be axially or radially inserted in the stator core. A combination of axial and radial insertion techniques may be used to insert the first and second conductor.

The at least one first conductor may have a first cross-sectional area (in transverse section). The at least one second conductor may have a second cross-sectional area On transverse section). The second cross-sectional area may be larger than the first cross-sectional area.

The or each first conductor may be referred to as minor conductors due to the lesser first radial dimension. The or each second conductor may be referred to as major conductor due to the larger second radial dimension.

The at least one first conductor may be separated from the at least one second conductor in each slot. The at least one first conductor may be offset from the at least one second conductor in the radial direction.

The at least one first conductor may have a first transverse dimension (extending perpendicular to the first radial dimension). The at least one second conductor may have a second transverse dimension (extending perpendicular to the first radial dimension). The first and second transverse dimensions may be different from each other. For example, the first transverse dimension may be less than the second transverse dimension. At least in certain embodiments, the first and second transverse dimensions may be at least substantially the same as each other. At least in certain embodiments, the first and second conductors have at least substantially the same cross-sectional area as each other in a plane extending tangential to the radial direction.

The or each first conductor may be substantially the same length as the or each second conductor.

A plurality of the first conductors may be provided in each slot. The first conductors in each slot may have substantially the same configuration. For example, the first conductors in each slot may all have the same first radial dimension in said radial direction. A plurality of the second conductors may be provided in each slot. The second conductors in each slot may have substantially the same configuration. For example, the second conductors may all have the same second radial dimension in said radial direction.

The or each first conductor may be disposed in a radially outer region of each slot. The second conductors may be disposed in a radially inner region of each slot.

Alternatively, the or each first conductor may be disposed in a radially inner region of each slot. The radially inner region may be disposed adjacent to a slot opening. The second conductors may be disposed in a radially outer region of each slot. This arrangement is advantageous as the eddy currents developed by a pulsating magnetic field are largest closest to the slot openings as the magnetic field density is highest at the slot opening. A, then the conductor closest to the slot openings will be most affected by additional losses generated by eddy currents.

The relationship between the number of the first conductors in each slot to the number of the second conductors in each slot may be defined by a whole number integer. The whole number integer may be an even number. Each slot may comprise two or more of the first conductors for each second conductor. The first radial dimension may be approximately half of the second radial dimension. The combined first radial dimension of two of the first conductors may be substantially equal to the second radial dimension of one of the second conductors. Each slot of the stator may comprise three of the first conductors for each second conductor. The first radial dimension may be approximately one third of the second radial dimension. The combined first radial dimension of three of the first conductors may be substantially equal to the second radial dimension of one of the second conductors.

The or each first conductor may comprise a formed conductor. The or each first conductor may be formed prior to insertion into the slot in the stator core. To facilitate assembly of the stator, two or more of the first conductors may be electrically connected to each other, for example to form a parallel circuit, prior to insertion into the stator core. The or each first conductor in each slot may each be formed by a leg portion of a first U-shaped conductor. The leg portion of the first U-shaped conductor may have the first radial dimension in the substantially radial direction. The or each first conductor may have other shapes or profiles.

The or each second conductor may comprise a formed conductor. The or each second conductor may be formed prior to insertion into the slot in the stator core. The or each second conductor in each slot may be formed by a leg portion of a second U-shaped conductor. The leg portion of the second U-shaped conductor may have the second radial dimension in the substantially radial direction. The or each second conductor may have other shapes or profiles.

The at least one first conductor and the at least one second conductor may have the same length in a longitudinal direction. The longitudinal direction may extend along a longitudinal axis of the electric machine, for example parallel to a rotational axis of a rotor associated with the stator.

The first conductor and/or the second conductor may comprise or consist of a hairpin winding.

A plurality of the first conductors may be provided in each slot. At least in certain embodiments, an even number of the first conductors is provided in each slot. The first conductors in each slot may be radially offset from each other. The first conductors in each slot may be disposed in one or more rows. A plurality of the rows may be formed in each slot, the rows being radially offset from each other. The rows may each comprise at least one of the first conductors. At least in certain embodiments, each row may comprise two or more of the first conductors.

A first subset of the first conductors in each slot may comprise two or more first conductors electrically connected to each other in parallel. The first conductors in the first subset may be arranged in a first sub-assembly. The first conductors in the first sub-assembly may be arranged in a stacked or nested configuration. The stator may comprise a plurality of the first sub-assemblies. For example, each phase winding may comprise a plurality of the first sub-assemblies. The first sub-assemblies may be connected to each other in series, for example by a weld or a crimp.

The first subset may comprise two or more of the conductors connected in parallel to each other to form each first sub-assembly. The radial position of the conductors in the first sub-assembly may alternate relative to each other in consecutive slots in a phase winding. For example, the radial position of first and second conductors in the first sub-assembly may alternate between inner and outer positions relative to each other in consecutive slots in the phase winding.

A second subset of the first conductors in each slot may comprise two or more first conductors electrically connected to each other in parallel. At least in certain embodiments, different first conductors form the first subset that those forming the second subset.

The first conductors in the second subset may be arranged in a second sub-assembly. The first conductors in the second sub-assembly may be arranged in a stacked or nested configuration. The stator may comprise a plurality of the second sub-assemblies. For example, each phase winding may comprise a plurality of the second sub-assemblies. The second subassemblies may be connected to each other in series, for example by a weld or a crimp.

The second subset may comprise two or more of the conductors connected in parallel to each other to form each second sub-assembly. The radial position of the conductors in the second sub-assembly may alternate relative to each other in consecutive slots in a phase winding.

For example, the radial position of first and second conductors in the second sub-assembly may alternate between inner and outer positions relative to each other in consecutive slots in the phase winding.

Alternatively, or in addition, the relative radial positions of the first and second sub-assemblies may alternate relative to each other. For example, the radial position of the first and second sub-assemblies may alternate between inner and outer positions relative to each other in consecutive slots in the phase winding.

The first conductors in the first subset may oppose the first conductors in the second subset.

A radially innermost one of the first conductors in each slot may be electrically connected via a series connection to a radially outermost one of the first conductors in the next slot in the same phase.

At least one first conductor may be disposed between the radially innermost one of the first conductors in each slot and the radially outermost one of the first conductors in each slot. Three, four, five, six or more first conductors may be disposed in each slot. First and second intermediate first conductors may be disposed between the radially innermost first conductor in each slot and the radially outermost first conductors in each slot. The first and second intermediate first conductors may be electrically connected to each other in parallel.

A plurality of the second conductors may be provided in each slot. At least in certain embodiments, an even number of the second conductors is provided in each slot. The second conductors in each slot may be radially offset from each other.

The stator may comprise two of the second conductors. Alternatively, or in addition, the relative radial positions of the second conductors may alternate relative to each other. For example, the radial position of first and second of the second conductors may alternate between inner and outer positions relative to each other in consecutive slots in the phase winding.

According to a further aspect of the present invention there is provided a stator for an electric machine, the stator comprising: a cylindrical stator core comprising a plurality of slots, each of the slots extending in a substantially radial direction; at least one first conductor disposed in each slot, the or each first conductor having a first transverse dimension perpendicular to a radial direction; and at least one second conductor disposed in each slot, the or each second conductor having a second transverse dimension perpendicular to the radial direction; wherein the first transverse dimension is less than the second transverse dimension.

The or each first conductor may have a first radial dimension along the radial direction. The or each second conductor may have a second radial dimension along the radial direction. The first radial dimension and the second radial dimension may be at least substantially the same as each other. Alternatively, the first radial dimension may be less than the second radial dimension.

According to a further aspect of the present invention there is provided a stator for an electric machine, the stator comprising: a cylindrical stator core comprising a plurality of slots; a plurality of conductors disposed in each slot; wherein a first subset of the conductors in each slot are electrically connected to each other in parallel.

Each of the conductors may be electrically insulated. For example, the conductors may have an outer insulating layer, for example comprising a film or coating.

The first subset comprises two or more of the conductors. The conductors in the first subset are connected to each other in parallel. The first subset of the conductors may be arranged in a first sub-assembly. The conductors in the first sub-assembly may be arranged in a stacked or nested configuration. The stator may comprise a plurality of the first sub-assemblies. For example, each phase winding may comprise a plurality of the first sub-assemblies. The first sub-assemblies may be connected to each other in series, for example by a weld or a crimp.

A second subset of the conductors in each slot may be electrically connected to each other in parallel. The conductors in the first subset may be different from the conductors in the second subset. In other words, the first and second subsets may be non-overlapping.

The second subset comprises two or more of the conductors. The conductors in the second subset are connected to each other in parallel. The second subset of the conductors may be arranged in a second sub-assembly. The conductors in the second sub-assembly may be arranged in a stacked or nested configuration. The stator may comprise a plurality of the second sub-assemblies. For example, each phase winding may comprise a plurality of the second sub-assemblies. The second sub-assemblies may be connected to each other in series, for example by a weld or a crimp.

The first and second sub-assemblies may be arranged in opposition to each other.

The stator core may comprise a plurality of stator teeth. One or more of the conductors may be wound around the stator teeth. The one or more of the conductors may be radially inserted in the stator core. Alternatively, or in addition, one or more of the conductors may comprise a formed conductor which is disposed in the slots. One or more of the conductors may be axially inserted in the stator core. A combination of axial and radial insertion techniques may be used to insert the conductors.

The conductors may each have a single core. The conductors may each have a single strand (rather than a plurality of strands or filaments). The conductors may each consist of a solid wire. The conductors may have a circular cross-section. Alternatively, the conductors may have an elliptical cross-section or a rectangular cross-section.

Alternatively, or in addition, the conductors may each comprise a plurality of strands (or filaments). The conductors may, for example, each comprise a plurality of film-insulated strands. The strands may be twisted or braided. The strands may be compressed or compacted, for example into a rectangular profile. The conductor may comprise a Litz wire, for example a twisted or braided Litz wire. The Litz wire may optionally be compacted, for example to provide a rectangular cross-section.

The first subset may comprise two or more of the conductors connected in parallel to each other to form a first sub-assembly. The radial position of the conductors in the first subassembly may alternate relative to each other in consecutive slots in a phase winding. For example, the radial position of first and second conductors in the first sub-assembly may alternate between inner and outer positions relative to each other in consecutive slots in the phase winding.

The second subset may comprise two or more of the conductors connected in parallel to each other to form a second sub-assembly. The radial position of the conductors in the second subassembly may alternate relative to each other in consecutive slots in a phase winding. For example, the radial position of first and second conductors in the second sub-assembly may alternate between inner and outer positions relative to each other in consecutive slots in the phase winding.

The first and second sub-assemblies may form a first conductor of the type described herein having a first radial dimension. The stator may comprise at least one second conductor of the type described herein having a second radial dimension. As described herein, the first radial dimension may be less than the second radial dimension.

According to a further aspect of the present invention there is provided a stator for an electric machine, the stator comprising: a cylindrical stator core comprising a plurality of slots; first, second and third phase windings, each of the first, second and third phase windings comprising a plurality of first conductors and a plurality of second conductors, the first conductors being different from the second conductors; wherein the first, second and third phase windings may be arranged in a delta configuration or a star configuration for connection to an inverter. The first conductors may be connected in series to the second conductors in each of the first, second and third phase windings.

According to a further aspect of the present invention there is provided a stator for an electric machine, the stator comprising: a cylindrical stator core comprising a plurality of slots; a plurality of first conductors arranged in a delta configuration or a star configuration for connection to a first inverter; and a plurality of second conductors arranged in a delta configuration or a star configuration for connection to a second inverter.

The first conductors and the second conductors may be arranged in respective first and second star configurations. Alternatively, the first conductors and the second conductors may be arranged in respective first and second delta configurations. In a variant, the first conductor may be arranged in a delta configuration and the second conductor may be arranged in a star configuration (or vice versa). The delta configuration is typically easier to manufacture than a star configuration, but may cause loss-inducing circulating currents.

The stator may comprise first, second and third phase windings. Each of the first, second and third phase windings may comprise a plurality of the first conductors. Alternatively, or in addition, each of the first, second and third phase windings may comprise a plurality of the second conductors.

The first conductors may be connected in series to the second conductors in each of the first, second and third phase windings. The first, second and third phase windings may be arranged in a delta configuration or a star configuration for connection to an inverter.

The first conductors in each of the first, second and third phase windings may be arranged in a delta configuration or a star configuration for connection to a first inverter. Alternatively, or in addition, the second conductors in each of the first, second and third phase windings may be arranged in a delta configuration or a star configuration for connection to a second inverter. The first and second inverters may be controllable together or independently of each other.

According to a still further aspect of the present invention there is provided a controller for controlling operation of the electric machine described herein. The controller may, for example, control operation of the or each inverter.

According to a further aspect of the present invention there is provided an electric machine comprising a stator as described herein. The electric machine may comprise a rotor. The rotor may be configured to rotate relative to the stator.

According to a still further aspect of the present invention there is provided a vehicle comprising one or more electric machines as described herein.

The references herein to a radial direction refer to a radius extending from a centre of the stator core. The transverse dimension(s) described herein may be understood as referring to dimensions measured in a circumferential or tangential direction.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle comprising an electrical machine in accordance with an embodiment of the present invention; Figure 2 shows a longitudinal sectional view of the electrical machine shown in Figure 1; Figure 3 shows a transverse sectional view of the electrical machine shown in Figure 1; Figure 4 shows a transverse cross section of a first slot of the stator of the electrical machine shown in Figure 1; and Figure 5 shows a transverse cross section of a first slot of a stator for comparative purposes; Figure 6 shows first and second electrical connection diagrams illustrating the electrical connections in each minor phase winding and each major phase winding; Figure 7A shows a first star configuration for connecting the phase windings to a single inverter; Figure 7B shows a second star configuration for connecting the phase windings in the stator to first and second inverters; Figure 8A shows a first delta configuration for connecting the phase windings to a single inverter; Figure 8B shows a second delta configuration for connecting the phase windings in the stator to first and second inverters; Figures 9A, 9B and 9C show variants of the stator described herein with reference to Figure 1.

DETAILED DESCRIPTION

An electric machine 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures. As illustrated in Figure 1, the electric machine 1 has particular application as an electric drive unit (EDU) in a vehicle V, such as an automobile, a utility vehicle or a tractor unit. In use, the EDU generates a force to propel the vehicle V. The EDU may be used independently, for example in a BEV application; or in conjunction with an internal combustion engine (not shown), for example in a HEV application or a PHEV application. However, it will be understood that the electric machine 1 may be used in other applications.

As shown in Figure 2, the electric machine 1 comprises a housing 2, a rotor assembly 3, a stator 4 and a drive shaft 5. The electric machine 1 is described herein with reference to a longitudinal axis X about which the drive shaft 5 rotates. The rotor assembly 3 comprises a rotor (core) 6 which is mounted to the drive shaft 5 (shown in Figure 3). The rotor 6 is fixedly mounted to the drive shaft 5 such that the rotor 6 and the drive shaft 5 rotate together. An air gap G is maintained between the rotor Sand the stator 4. The rotor 6 is made up of a plurality of laminations of a ferromagnetic material to form a rotor iron (or rotor core).

The electric machine 1 in the present embodiment is a permanent magnet synchronous motor. As shown in Figure 3, the rotor 6 comprises six (6) rotor poles 9-n. The rotor poles 9-n each extend radially outwardly from the longitudinal axis X. The rotor poles 9-n each have a direct axis dr-n and a quadrature axis qr-n. The rotor poles 9-n have an equal angular spacing (i.e. a pitch of 60° between the direct axes dr-n of adjacent rotor poles 9-n). The rotor poles 9-n in the present embodiment each comprise at least one permanent magnet 10 mounted in the rotor 6. The rotor poles 9-n in the present embodiment each comprise three (3) magnets 10 (represented in Figure 3 by dashed lines) which are radially offset from each other within the rotor 6. It will be understood that the rotor 6 can comprise less than or more than eight (8) rotor poles. Each rotor pole 9-n may comprise less than or more than three (3) permanent magnets 10. In further variants, the permanent magnets 10 may be arranged in a single row, two rows, or more than three rows. Moreover, one or more permanent magnet 10 may be provided in one or more of the rows. In the present embodiment, each rotor pole 9-n comprises three (3) permanent magnets 10A, 10B, 100 located in respective magnet receiving apertures 11(a), 11(b), 11(c). The permanent magnets 10A, 10B, 100 in each rotor pole 9-n are spaced apart from each other in a radial direction. In particular, the permanent magnets 10A, 10B, 100 are arranged in an inner row A, an intermediate row B and an outer row C respectively. Other rotor configurations are contemplated. The rotor 6 may comprise less than or more than six (6) rotor poles 9-n. For example, the rotor 6 may comprise eight (8) rotor poles 9-n.

As shown in Figure 3, the stator 4 comprises a cylindrical stator core 12. The stator core 12 is composed of a plurality of laminations of a ferromagnetic material. The stator core 12 comprises a plurality of slots 13-n extending radially inwardly. The stator 4 in accordance with an aspect of the present invention comprises a dual winding. The dual winding comprises at least one minor winding for each phase (i.e. at least one phase minor winding); and at least one major winding for each phase (i.e. at least one phase major winding). The minor winding(s) and the major winding(s) may be powered by a single inverter. Alternatively, the minor winding(s) and the major winding(s) may be powered by separate inverters.

As shown in Figure 4, at least one minor conductor 14-n and at least one major conductor 15-n are disposed in each slot 13-n of the stator 4. The or each minor conductor 14-n is electrically insulated, for example by an outer coating, film or insulator (not shown). The or each major conductor 15-n is electrically insulated, for example by an outer coating, film or insulator (not shown). The minor conductors 14-n are connected to form a minor winding for each phase; and the major conductors 15-n are connected to form a major winding for each phase. The or each minor conductor 14-n has a smaller cross-sectional area than the or each major conductor 15-n. When located in the slot 13-n, the or each minor conductor 14-n has a first radial dimension RD1 extending in a radial direction; and a first transverse dimension TD1 extending in a tangential direction (perpendicular to the radial direction). When located in the slot 13-n, the or each major conductor 15-n has a second radial dimension RD2 extending in a radial direction; and a second transverse dimension extending TD1 in a tangential direction (perpendicular to the radial direction). The first radial dimension RD1 of the or each minor conductor 14-n is less than the second radial dimension RD2 of the or each major conductor 15-n. The first transverse dimension TD1 of the or each minor conductor 14-n is substantially equal to the second transverse dimension TD1 of the or each major conductor 15-n. The at least one minor conductor 14-n and the at least one major conductor 15-n have substantially the same length.

In the present embodiment, each slot 13-n comprises a plurality of the minor conductors 14n; and a plurality of the major conductors 15-n. The minor conductors 14-n are radially inset from the major conductors 15-n in the present embodiment. In particular, the minor conductors 14-n are disposed in a radially inner region RIN of the slots 13-n; and the major conductors 15-n are disposed in a radially outer region ROUT of the slots 13-n. In use, the minor and major conductors 14-n, 15-n are selectively energized to generate a torque to drive the rotor 6. In the present embodiment, the minor and major conductors 14-n, 15-n each comprise a hairpin winding. Each of the minor and major conductors 14-n, 15-n are U-shaped and comprise substantially parallel legs which allow radial insertion into the slot 13-n. The minor conductors 14-n in each slot 13-n have substantially the same configuration; and the major conductors 15-n in each slot 13-n have substantially the same configuration. The minor and major conductors 14-n, 15-n are electrically connected to each other by one or more weld.

The connections formed between the minor and major conductors 14-n, 15-n are described in more detail herein. The composition of the minor and major conductors 14-n, 15-n in a first slot 13-1 will now be described.

The first slot 13-1 extends in a first radial direction R1 (perpendicular to the longitudinal axis X). A central radial axis of each of the minor and major conductors 14-n, 15-n in the first slot 13-1 extends in said radial direction R1. The arrangement of the minor and major conductors 14-n, 15-n in the first slot 13-1 is shown in Figure 4. In the present embodiment, four (4) of said minor conductors 14-n, and two (2) of said major conductors 15-n are mounted in the first slot 13-1. The first, second, third and fourth minor conductors 14-1 are labelled A to D from a radially innermost position to a radially outermost position. The first and second major conductors 15-1 are labelled (a) to (b) from a radially innermost position to a radially outermost position. A first minor conductor 14-1(a) is disposed in a first radial position (the radially innermost position); a second minor conductor 14-1(b) is disposed in a second radial position; a third minor conductor 14-1(c) is disposed in a third radial position; and a fourth minor conductor 14-1(d) is disposed in the fourth radial position. A first major conductor 15-1(a) is disposed in a fifth radial position; and a second major conductor 15-1(b) is disposed in a sixth radial position (the radially outermost position). The minor and major conductors 14-n, 15-n are aligned with each other such that their respective common axes extend in the radial direction R1.

A transverse cross-section of the first slot 13-1 (in a plane extending perpendicular to the longitudinal axis X) is shown in Figure 3. The minor and major conductors 14-n, 15-n have at least substantially equal transverse dimensions TD1 (in a tangential direction perpendicular to the radial direction R1 within the transverse plane). In other words, the minor and major conductors 14-n, 15-n have substantially the same width. The minor and major conductors 14n, 15-n also have at least substantially equal longitudinal dimensions LD2 in a longitudinal direction extending along the length of the stator 4 parallel to the longitudinal axis X (shown in Figure 2). In other words, the minor and major conductors 14-n, 15-n all have substantially the same depth. It will be appreciated, therefore, that the minor and major conductors 14-n, 15-n all have at least substantially the same cross-sectional area in a tangential plane extending perpendicular to the radial direction R1.

The minor and major conductors 14-n, 15-n have different dimensions in the radial direction R1. In transverse section, the minor conductors 14-n each have the first radial dimension RD1 and the first transverse dimension TD1; and the major conductors 15-n each have the second radial dimension RD2 and the second transverse dimension TD1. The first radial dimension RD1 represents a radial extent of each minor conductor 14-n; and the second radial dimension RD2 represents a radial extent of each major conductor 15-n. As shown in Figure 4, the first and second transverse dimensions TD1 of the minor conductors 14-n and the major conductors 15-n are substantially equal to each other. However, the first radial dimension RD1 of each minor conductor 14-n is less than the second radial dimension RD2 of each major conductor 15-n. The minor conductors 14-n each have a smaller cross-sectional area than the major conductors 15-n in a radial plane (extending through the longitudinal axis X in a radial direction). The different radial dimensions represents a principal distinction between the minor and major conductors 14-n, 15-n. In the present embodiment, the first radial dimension RD1 is approximately half (50%) the second radial dimension RD2. Thus, the radial extent of the major conductors 15-n is approximately two times (x2) that of the minor conductors 14-n. Accordingly, the cross-sectional area of the major conductors 15-n in a radial plane (extending through the longitudinal axis X in a radial direction) is approximately two times (x2) the cross-sectional area of the minor conductors 14-n in the radial plane. Other whole integer multiples may define the ratio of the radial dimensions RD1. RD2 of the minor and major conductors 14-n, 15-n. For example, the first radial dimension RD1 may be approximately one third (33%) or one quarter (25%) of the second radial dimension RD2.

A transverse cross section of a first slot 113-1 of a stator 104 comprising four (4) conductors 114-1 is shown in Figure 5 for comparison purposes. The conductors 114-1 in the illustrated arrangement have at least substantially the same configuration as each other. In particular, the conductors 114-1 each having substantially the same radial dimension RD1'. By way of example, the first radial dimension RD1 according to the present embodiment is approximately half (i.e. 50%) of the radial dimension RD1 of each of the conductors 114-1; and the second radial dimension RD2 according to the present embodiment is substantially equal to the radial dimension RD1' of each of the conductors 114-1. The transverse dimension TD1 and the longitudinal dimension LD1 of the second conductors 15-n according to the present embodiment are substantially equal to the transverse dimension TD1' and the longitudinal dimension TD1' respectively of each of the conductors 114-1. The first and second minor conductors 14-1(a), 14-1(b) of the present embodiment are equivalent to the first conductor 114-1(a). The third and fourth minor conductors 14-1(c), 14-1(d) of the present embodiment are equivalent to the second conductor 114-1(b). The first major conductor 15-1(a) of the present embodiment is equivalent to the third conductor 114-1(c). The second major conductor 15-1(b) of the present embodiment is equivalent to the fourth conductor 114-1(d). The minor and major conductors 14-n, 15-n each have at least substantially the same cross-sectional area in the tangential plane as the conductors 114-1(a-d).

As outlined above, the minor conductors 14-n form a minor winding of each phase; and the major conductors 15-n form a major winding of each phase. The topology of the minor conductors 14-n forming a first phase ("U" phase) minor winding MN1 and the major conductors 15-n forming a first phase ("U" phase) major winding MJ1 will now be described with reference to Figure 6. A first electrical connection diagram 50A shows the electrical connections of the minor conductors 14-n in the first phase minor winding MN1. Only the minor conductors 14-n forming the first phase minor winding MN1 are shown in the first electrical connection diagram 50A. A second electrical connection diagram 50B shows the electrical connections of the major conductors 15-n in the first phase major winding MJ1. The electrical connections and welds between the minor conductors 14-n and the major conductors 15-n are illustrated in Figure 6. Only the major conductors 15-n forming the first phase major winding MJ1 are shown in the second electrical connection diagram 50B. It will be understood that the stator 4 comprises a second phase winding ("V" phase); and a third phase winding ("W" phase). The minor conductors 14-n have substantially the same configuration in a second phase ("V" phase) minor winding and a third phase ("W") phase minor winding. Similarly, the major conductors 15-n have substantially the same configuration in the second phase ("V" phase) major winding and the third phase ('W") phase major winding. It will be understood that the second and third phase windings are offset by integer times two thirds (2/3) of a pole step. The pole step in the present embodiment is six (6) slots 13-n; and the offset between the phase windings is equivalent to four (4) slots 13-n).

The first electrical connection diagram 50A represents each of the thirty-six (36) slots 13-n (where n is a whole number integer in the range one (1) to thirty-six (36) inclusive) within the stator 3. The position of each of the minor conductors 14-n relative to each other within each slot 13-n is also represented in the first electrical connection diagram 50A. In particular, the position of the minor conductors 14-n(a-d) in relation to the slot opening are shown from left to right in the first electrical connection diagram 50A. The first minor conductor 14-n(a) is shown to the left in each slot 13-n in the first electrical connection diagram 50A; and the fourth minor conductor 14-n(d) is shown to the right in each slot 13-n in the first electrical connection diagram 50A.

The connections of the minor conductors 14-n is shown in the first electrical connection diagram 50A. Each of the minor conductors 14-n is formed by an electrically conductive wire 51-n. As shown in the first electrical connection diagram 50A, the minor conductors 14-n are formed by first, second, third and fourth electrically conductive wires 51-n. The electrically conductive wires 51-n each have an elongated form and may, for example, comprise a single electrically conductive wire. In a variant, the electrically conductive wires 51-n may each comprise a plurality of strands (i.e. a multi-strand wire). The electrically conductive wires 51-n may comprise a plurality of film-insulated strands, for example compacted to form a rectangular cross-section. The first radial dimension RD1 and the first transverse dimension TD1 of each of the minor conductors 14-n are determined by the corresponding dimensions of the electrically conductive wire 51-n.

The electrically conductive wire 51-n may be pre-formed and inserted axially into the stator 4 during assembly. In a variant, the electrically conductive wire 51-n may be wound onto the teeth of the stator core, thereby radially inserting the electrically conductive wire 51-n. The electrically conductive wires 51-n may be inserted into the stator 4 individually. In the present embodiment, the electrically conductive wires 51-n are inserted into the stator 4 in nested sets, each nested set comprising two or more of the electrically conductive wires 51-n. After insertion into the stator 4, the electrically conductive wires 51-n are electrically connected to each other in series. Conventional techniques, such as welding or crimping, may be employed to connect the electrically conductive wires 51-n. In the present embodiment, the electrically conductive wires 51-n are connected by a plurality of welds (denoted generally by the reference numeral 52). Each weld 52 in the present embodiment electrically connects the ends of four (4) electrically conductive wires 51-n. The electrically conductive wires 51-n in each nested set may be electrically connected to each other prior to insertion into the stator 4, for example by performing a welding or crimping operation. After insertion, the electrically conductive wires 51-n in adjacent nested sets (positioned next to each other in a circumferential direction) may be connected to each other, for example by welding or crimping operations.

As shown in Figure 6, the electrically conductive wires 51-n are arranged in the slots 13-n a sub-assembly. The first and second electrically conductive wires 51-1, 51-2 form a first subassembly. Within the first nested arrangement, one of the first and second electrically conductive wires 51-1, 51-2 is disposed inside the other one of the first and second electrically conductive wires 51-1, 51-2 in a radial direction. The third and fourth electrically conductive wires 51-3, 51-4 form a second nested arrangement. Within the second nested arrangement, one of the third and fourth electrically conductive wires 51-3, 51-4 is at least partially nested inside the other one of the third and fourth electrically conductive wires 51-3, 51-4 in a radial direction. The electrically conductive wires 51-n have a generally V-or W-shaped topology (sinusoidal or serpentine) around the circumference of the stator 4 when viewed along the longitudinal axis X. Thus, the first and second electrically conductive wires 51-1, 51-2 are disposed alternately in radially inner and radially outer positions relative to each other. Similarly, the third and fourth electrically conductive wires 51-3, 51-4 are disposed alternately in radially inner and radially outer positions relative to each other. It will be understood that the relative position of the electrically conductive wires 51-n changes in each of the first and second nested arrangements around the stator 4.

The electrically conductive wires 51-n are connected to each other in parallel to form separate minor sub-assemblies 53-n of a first phase minor winding (denoted by the reference MN1). In the present embodiment, the first and second electrically conductive wires 51-1, 51-2 are connected in parallel to each other to form a first minor sub-assembly 53-1; and the third and fourth electrically conductive wires 51-3, 51-4 are connected in parallel to each other to form a second minor sub-assembly 53-2. Thus, the first minor sub-assembly 53-1 is composed of the first and second electrically conductive wires 51-1, 51-2 connected in parallel; and the second minor sub-assembly 53-2 is composed of the third and fourth electrically conductive wires 51-3, 51-4 connected in parallel. As shown in Figure 6, the beginning of the first minor sub-assembly 53-1 is labelled Si; and the end of the first minor sub-assembly 53-1 is labelled El. The beginning of the second minor sub-assembly 53-2 is labelled 52; and the end of the second minor sub-assembly 53-2 is labelled E2. The beginning Si, 52 of the first minor subassembly 53-1 and the second minor sub-assembly 53-2 are connected to each other to form a first end Ull of the first phase minor winding MN1. The ends El, E2 of the first minor sub-assembly 53-1 and the second minor sub-assembly 53-1 are connected to each other to form a second end U12 of the first phase minor winding MN1.

The first minor sub-assembly 53-1 and the second minor sub-assembly 53-2 form the minor conductors 14-n in the slots 13-n in the first phase minor winding MN1. The relative position of the first phase minor winding 53-1 and the second phase winding 53-2 alternates between slots 13-n in the same phase. By way of example, the first minor sub-assembly 53-1 is disposed in a radially inner position in the seventh slot 13-7; and in a radially outer position in the thirteenth slot 13-13 (which is the next slot 13-n in the same phase, i.e. offset by one pole step). Thus, the electrically conductive wires 51-n form different minor conductors 14-n in the different slots 13-n. The relative positions of the electrically conductive wires 51-n in a sequence of slots 13-n in the same phase will now be described with reference to Figure 6.

The first electrically conductive wire 51-1 forms the second minor conductor 14-7(b) in the seventh slot 13-7; and the third minor conductor 14-13(c) in the thirteenth slot 13-13. Thus, the second minor conductor 14-7(b) is connected in series to the third minor conductor 1413(c) in the next slot 13-13 in the same phase. The second electrically conductive wire 51-2 forms the first minor conductor 14-7(a) in the seventh slot 13-7; and the fourth minor conductor 14-13(d) in the thirteenth slot 13-13. Thus, the first minor conductor 14-7(a) is connected in series to the fourth minor conductor 14-13(d) in the next slot 13-13 in the same phase. The third electrically conductive wire 51-3 forms the third minor conductor 14-7(c) in the seventh slot 13-7; and the second minor conductor 14-13(b) in the thirteenth slot 13-13. Thus, the third minor conductor 14-7(c) is connected in series to the second minor conductor 14-13(b) in the next slot 13-13 in the same phase. The fourth electrically conductive wire 51-4 forms the fourth minor conductor 14-7(d) in the seventh slot 13-7; and the first minor conductor 14-13(a) in the thirteenth slot 13-13. Thus, the fourth minor conductor 14-7(d) is connected in series to the first minor conductor 14-13(a) in the next slot 13-13 in the same phase.

The connections of the major conductors 15-n are shown in the second electrical connection diagram 50B. Each of the major conductors 15-n is formed by an electrically conductive wire 61-n. As shown in the second electrical connection diagram 50B, the major conductors 15-n are formed by first and second electrically conductive wires 61-n. In The electrically conductive wires 61-n each have an elongated form and may, for example, comprise an electrically conductive wire. The second radial dimension RD2 and the second transverse dimension TD1 of each of the major conductors 15-n are determined by the corresponding dimensions of the electrically conductive wire 61-n. As described herein, the second radial dimension RD2 is greater than the first radial dimension RD1. To facilitate assembly of the stator 4, each electrically conductive wire 61-n is formed from a plurality of strands which are electrically connected to each other. The strands are pre-formed and inserted into the stator 4 during assembly. In the present embodiment, the strands are connected to each in series by a plurality of welds (denoted generally by the reference numeral 62). Other techniques may be utilised to connect the strands. The welds 62 are created after the strands have been inserted into the stator 4. As described herein, each weld 62 electrically connects the ends of two (2) strands to each other.

The electrically conductive wires 61-n are connected to each other in series to form separate major sub-assemblies 63-n to form a first phase major winding (denoted by the reference numeral MJ1 in Figure 6). In the present embodiment, the first conductive wires 61-1 are connected in series to form a first major sub-assembly 63-1; and the second electrically conductive wires 61-2 are connected in series to form a second major sub-assembly 63-2. As shown in Figure 6, the first major sub-assembly 63-1 is connected in series to the second major sub-assembly labelled Si. The first and second major sub-assemblies 63-1, 63-2 have respective first and second ends U21, U22 that form the ends of the first phase major winding MJ1.

This arrangement of the minor conductors 14-n may reduce or minimise the difference between the induced voltages in the minor sub-assemblies. Accordingly, the circulation currents between the minor sub-assemblies and additional losses in the conductors may be reduced. 1(b)1(d) The method of assembling the stator 4 will now be described with particular reference to the first slot 13-1. It will be understood that the same techniques are used in each of the other slots 13-n in the assembly process. The hairpin windings are formed from the minor conductors 14-1 which are generally U-shaped and each form a turn of a serial connection.

The parallel legs of the minor conductors 14-n are inserted axially into the first slot 13-1 in the stator core 12. The first and second minor conductors 14-1(a), 14-1(b) are placed in the first slot 13-1 in a radially innermost position which corresponds to the position of the first conductor 114-1(a) in the stator 104. The third and fourth minor conductors 14-1(c), 14-1(d) are placed in the first slot 13-1 in an intermediate position which corresponds to the position of the second conductor 114-1(b) in the stator 104. The first and second major conductors 15-1(a), 15-1(b) are placed in the first slot 13-1 in a radially outermost position which corresponds to the position of the third and fourth conductors 114-1(C-D) respectively in the stator 104. The ends of each of the minor conductors 14-1(a), 14-1(b), 14-1(c), 14-1(d) and ends of the major conductors 15-1(a), 15-1(b) are bent after insertion into the first slot 13-1. The minor conductors 14-1(a), 14-1(b), 14-1(c), 14-1(d) are connected to the minor conductors 14-1(a), 14-1(b), 14-1(c), 14-1(d) in the next slot 13-n having the same phase to provide the topology described herein. A similar technique is implemented to insert and connect the major connectors 15-n(e), 15-n(f) in the slots 13-n. In the present embodiment, a welding operation is performed to form the welds 52 which electrically connect the minor conductors 14-n and the major conductors 15-n. This process is also performed in respect of the second and third phase windings to assemble the stator 4. It The rotor assembly 3 and the rotor 6 are assembled in conventional manner.

The electrical connection of the stator 4 will now be described with reference to Figures 7A, 7B, 8A and 8B. As outlined above, the stator 4 has a dual winding configuration in which each phase winding comprises minor conductors 14-n and major conductors 15-n. The phase windings can be connected in a star (Y-shaped) configuration or a delta configuration. In the star configuration, the windings are connected to a central point (parallel circuits) and power is applied to the other end of each winding. In the delta configuration, the windings are connected to each other (series circuits) in a triangle-like arrangement and the power is applied at each connection.

A first configuration of the phase windings (denoted generally by the reference numeral 60) is shown in Figure 7A. In the first configuration 60, the stator 4 is connected in a single star configuration to a first inverter 20A. The minor conductors 14-n and the major conductors 15n in each phase winding are connected to each other in series. For example, the first phase minor winding MN1 is connected in series to the first phase major winding MJ1. This configuration is implemented for the first, second and third phases of the stator 4. The phase windings are connected to the first inverter 20A in a first star configuration 61. A controller (not shown) is provided for controlling operation of the first inverter 20A.

A second configuration of the phase windings (denoted generally by the reference numeral 70) is shown in Figure 7B. In the second configuration 110, the stator 4 is connected in a double star configuration to a first inverter 20A and a second inverter 20B. The minor conductors 14-n in each phase are connected to the first inverter 20A in a first star configuration 71. The major conductors 15-n in each phase are connected to the second inverter 20B in a second star configuration 72. Thus, the minor winding and the major winding for each phase are connected to different inverters 20A, 20B. This arrangement enables independent control of the minor winding and the major winding in each phase. One or more controller (not shown) is provided for controlling operation of the first inverter 20A and the second inverter 20B. This arrangement enables independent control of the power supplied to the minor windings and the major windings.

A third configuration of the phase windings (denoted generally by the reference numeral 80) is shown in Figure 8A. In the third configuration 120, the stator 4 is connected in a single delta configuration to a first inverter 20A. The minor conductors 14-n and the major conductors 15-n in each phase winding are connected to each other in series. For example, the first phase minor winding MN1 is connected in series to the first phase major winding MJ1. The first inverter 20A supplies power at the connections between each phase winding. A controller (not shown) is provided for controlling operation of the first inverter 20A.

A fourth configuration of the phase windings (denoted generally by the reference numeral 90) is shown in Figure 8B. In the fourth configuration 130, the stator 3 is connected in a double delta configuration to a first inverter 20A and a second inverter 20B. The minor conductors 14n in each phase are connected to the first inverter 20A in a first delta configuration 91. The major conductors 15-n in each phase are connected to the second inverter 20B in a second star configuration 92. Thus, the minor winding and the major winding for each phase are connected to different inverters 20A, 20B. This arrangement enables independent control of the power supplied to the minor windings and the major windings. One or more controller (not shown) is provided for controlling operation of the first inverter 20A and the second inverter 20B.

In a further variant, the minor windings are connected in a star configuration (as shown in Figure 7B, for example) and the major windings are connected in a delta configuration (as shown in Figure 8B, for example). Alternatively, the minor windings are connected in a delta configuration (as shown in Figure 8B, for example) and the major windings are connected in a star configuration (as shown in Figure 7B, for example).

The eddy current losses in the minor conductors 14-n disposed in the slots 13-1 of the electrical machine 1 may be reduced. This reduction is a result of the use of first, second, third and fourth minor conductors 14-1(a), 14-1(b), 14-1(c), 14-1(d) having a first radial dimension RD1 that is smaller than the first radial dimension RD1' of first and second conductors 114- 1(a), 114-1(b) in a comparable stator 104. The smaller first radial dimension RD1 reduces the area of the surface perpendicular to the magnetic flux lines in the stator 4. The electrical circuit in which the eddy currents flow has a lower induced voltage. The smaller cross section of the minor conductors 14-1(a), 14-1(b), 14-1(c), 14-1(d) increases resistance. The lower induced voltage and/or the higher resistance may result in significantly lower losses in the arrangement of the minor conductors 14-n. At least in certain embodiments, the first radial dimension RD1 has little or no effect of peak operating characteristics of the electric machine 1. In the present embodiment, the length of the minor conductors 14-n is at least substantially unchanged (compared to the conductors 114-n of the stator 104). Thus, the capabilities of the electric machine 1, such as torque and/or power, may be maintained.

The embodiments of the present invention comprise minor conductors 14-n which have a smaller radial dimension RD1 than that of the major conductors 15-n. The minor conductors 14-n and the major conductors 15-n have been described as having the same transverse dimension TD1. In a variant, the minor conductors 14-n may have a smaller transverse dimension TD1 than that of the major conductors 15-n. First and second variants are shown in Figures 9A and 9B respectively. The minor conductors 14-n each have a first transverse dimension TD1 and a first radial dimension RD1. The major conductors 14-n each have a second transverse dimension TD2 and a second radial dimension RD2. In the first variant, the first transverse dimensions TD1 is approximately half (50%) of the second transverse dimension TD2. In the second variant, the first transverse dimension TD1 is approximately one quarter (25%) of the second transverse dimension TD2. The minor conductors 14-n are shown in the first and second variants as having a first radial dimension RD1 which is approximately one quarter (25%) of the second radial dimension RD2.

The transverse dimension TD1 may be varied in conjunction with, or instead of, changes to the radial dimension RD1. A third variant is shown in Figure 9C. The first transverse dimension TD1 is approximately one third (33%) of the second transverse dimension TD2. The first radial dimension RD1 is approximately half (50%) of the second radial dimension RD2. The first transverse dimension TD1 may be approximately one fifth (20%), one quarter (25%) or one half (500A) of the second transverse dimension TD2.

It will be understood that various changes and modifications can be made to the stator 4 described herein without departing from the present invention. For example, the minor conductors 14-n and the major conductors 15-n have been described herein as being inserted axially into the slots 13-n formed in the stator core. It will be understood that the minor conductors 14-n and/or the major conductors 15-n may be inserted radially into the slots 13-n formed in the stator core.

The electric machine 1 described herein is a permanent magnet motor in which the rotor 6 comprises a plurality of rotor poles 9-n each having one or more permanent magnet 10. It will be understood that the stator 4 described herein is not limited to this type of motor or rotor configuration. The aspects of the minor conductors 14-n and/or the major conductors 14-n described herein may be employed in any type of electrical machine that can operate with distributed windings. For example, the stator 4 described herein may be used in an induction motor or a wound field synchronous motor.

Claims

CLAIMS1. A stator for an electric machine, the stator comprising: a cylindrical stator core comprising a plurality of slots, each of the slots extending in a substantially radial direction; at least one first conductor disposed in each slot, the or each first conductor having a first radial dimension in the substantially radial direction; and at least one second conductor disposed in each slot, the or each second conductor having a second radial dimension in the substantially radial direction; wherein the first radial dimension is less than the second radial dimension.
2. A stator as claimed in claim 1, wherein the at least one first conductor is disposed in a radially inner region of each slot; and the at least one second conductor is disposed in a radially outer region of each slot.
3. A stator as claimed in claim 1 or claim 2, wherein each slot of the stator comprises two of the first conductors for each second conductor.
4. A stator as claimed in any one of claims 1, 2 or 3, wherein the first radial dimension is approximately half of the second radial dimension.
5. A stator as claimed in any one of the preceding claims, wherein the or each first conductor in each slot is formed by a leg portion of a first U-shaped conductor; and the or each second conductor in each slot is formed by a leg portion of a second U-shaped conductor.
6. A stator as claimed in claim 5, wherein the leg portion of the first U-shaped conductor has the first radial dimension; and the leg portion of the second U-shaped conductor has the second radial dimension.
7. A stator as claimed in any one of the preceding claims, wherein the at least one first conductor and the at least one second conductor have the same length in a longitudinal direction.
S. A stator as claimed in any one of the preceding claims comprising a plurality of the first conductors in each slot.
9. A stator as claimed in claim 8, wherein a first subset of the first conductors in each slot comprises two or more first conductors electrically connected to each other in parallel.
10. A stator as claimed in claim 9, wherein the first conductors in the first subset are arranged in a first sub-assembly.
11. A stator as claimed in any one of claims 8 to 10, wherein a second subset of the first conductors in each slot comprises two or more first conductors electrically connected to each other in parallel, wherein different first conductors forming the first subset are different from those forming the second subset.
12. A stator as claimed in claim 11, wherein the first conductors in the second subset are arranged in a second sub-assembly.
13. A stator as claimed in any one of claims 8 to 12, wherein a radially innermost one of the first conductors in each slot is electrically connected via a series connection to a radially outermost one of the first conductors in the next slot in the same phase.
14. A stator as claimed in claim 13, wherein at least one of the first conductors is disposed between the radially innermost one of the first conductors in each slot and the radially outermost one of the first conductors in each slot.
15. A stator as claimed in claim 14, wherein two of the first conductors are disposed between the radially innermost one of the first conductors in each slot and the radially outermost one of the first conductors in each slot.
16. A stator as claimed in any one of the preceding claims comprising first, second and third phase windings, each of the first, second and third phase windings comprising a plurality of the first conductors and a plurality of the second conductors.
17. A stator as claimed in claim 16, wherein the first conductors are connected in series to the second conductors in each of the first, second and third phase windings, wherein the first, second and third phase windings are arranged in a delta configuration or a star configuration for connection to an inverter.
18. A stator as claimed in claim 17, wherein the first conductors in each of the first, second and third phase windings are arranged in a delta configuration or a star configuration for connection to a first inverter; and the second conductors in each of the first, second and third phase windings are arranged in a delta configuration or a star configuration for connection to a second inverter.
19. An electric machine comprising a stator as claimed in any one of the preceding claims.
20. A controller for controlling operation of the electric machine claimed in claim 19.
21. A vehicle comprising one or more electric machines as claimed in claim 19.