GB2490901A - A coil arrangement for a multi-phase electrical machine - Google Patents

Abstract

A coil arrangement for an N-phase electrical machine WI includes a first coil 10a and N-1 separate interlocking coils 10b, 10c each including a strip of electrically conductive material that is wound to form a coil having multiple windings circumscribing a hollow core with air gaps between adjacent windings. Ferromagnetic material 1, or a stack of ferromagnetic slices, is disposed within at least some of the air gaps. The first coil 10a serves as an anchor for 10 supporting the N-1 remaining coils and the hollow core of the first coil 10a is dimensioned to accommodate the N-1 remaining coils without shorting between coils. Each remaining N-1 coil 10b, 10c can have a stepped part 21 that is mounted within the hollow core of the first coil 10a. The N-1 coils can be mounted either side of the first coil and, for a five phase or greater machine each successive pair of coils have a deeper stepped portion 21. The coils can be connected using vias or jumpers (fig 4, 12) with unconnected ends (fig 5, 26,27) connected to a source of current. The coil can be used in an axial flux electrical machine such as an induction motor having a rotor (fig 6, 31) with inner and outer rims connected by radial conductive spokes or a radial flux machine having a rotor cage with end plates and axial conductors (Fig 9, 47). In each case ferromagnetic material (fig 7, 17) is disposed within the gaps between the conductors.

Description

Coil arrangement for multi-phase electrical machine

FIELD OF THE INVENTION

The present invention relates to electric motors and electric generators and regenerative electric devices.

BACKGROUND OF THE INVENTION

The vast majority of conventional electric motors have stator cores constructed from sheets of laminated steel. The individual laminations are punched from flat sheets of steel using specially constructed dies with the necessary shape of slots and teeth incorporated in them. Laminations made by this method are coated with a thin insulation layer, and then multiple laminations are stacked together to form the complete laminated stator. The construction of the stator core with the laminations separated by layers of very thin insulation reduces iron losses in the stator.

A second, though less widely used, construction involves cold pressing raw metal powder or powdered ferromagnetic material into an appropriate shape, is followed by sintering the product to improve its mechanical properties.

For example, U.S. Patent No. 6,603,237 describes an electrical machine whose rotor poLes are formed from laminations of magnetic materials such as iron or thin film soft ferromagnetic materials.

US Pat. No. 5,097,167 discloses an armature coil assembly for magnet-type rotary electric machines, which comprises flat conductor pieces or segments with large-area sides thereof arranged parallel to the direction of the magnetic fluxes of a permanent magnet, and a ferromagnetic member inserted between the conductor pieces. The ferromagnetic member inserted provides a magnetic anisotropy in the armature coil along the axis of coil rotation. Thus the flow of magnetic fluxes from the magnet through the armature coil to the machine core is facilitated thereby to reduce leakage magnetic fluxes. A stator coil assembly is also made up by using like coil conductor segments.

US Pat. No. 5,319,844 discloses a method of making an electromagnetic transducer by fabricating a plurality of elongated high permeability flux carrying members, and preparing multiple wire bundles each having a predetermined length. The wire bundles are wound to provide a distributed winding configuration s having a plurality of elongated open spaces into which the plurality of flux carrying members are inserted to provide a winding/flux carrying member assembly. A bonding material is provided around the winding/flux carrying member assembly to provide a rigid structure.

US Pat. No, 3,237,036 discloses in Fig. 3 a similar coil structure having planar electrical conductors in between which there are interposed flat magnetic conductors.

WO 2001/47089 discloses an electrical machine whose stator has radial conducting strips interleaved with iron laminations,

SUMMARY OF THE INVENTION

According to the invention there is provided a coil arrangement for an N-phase electrical machine (N>i), said coil arrangement comprising a first coil and N-i separate interlocking coils, each of said coils comprising: a strip of electrically conductive material that is wound to form a coil having multiple windings circumscribing a hollow core with air gaps between proximate surfaces of adjacent windings, and ferromagnetic material disposed within at least some of the air gaps; wherein: the first coil serves as an anchor for supporting the N-i remaining coils; and the hollow core of the first coil is dimensioned to accommodate therein N-i remaining coils without mutual shorting between two or more coils.

An electrical machine having such a coil arrangement is less expensive, as well as being more efficient and lightweight than known machines of so comparable torque and/or power.

The coil arrangement according to the invention may be employed in the stator core, the coil windings including conductors that are preferably made from non-ferromagnetic materials, such as copper or aluminum, although they may include ferromagnetic materials. The rotor may be built from two or more discs each of which may be made by permanent magnets exploiting the Halbach structure or any other suitable structure.

An electrical machine employing such a coil arrangement may be an electric motor, an electric generator or a regenerative electric motor. The machine includes at least one stator arrangement having a plurality of electromagnetic io assemblies each including a multi-winding coil having many small pieces of ferro-magnetic material disposed between the windings. At least one rotor may include two or more discs, for rotation about a given rotation axis within a certain range of operating rotational speeds. The rotor arrangement includes a plurality of rotor poles for magnetically interacting with the stator poles, the rotor poles rotating about the rotational axis. The machine also includes a switching arrangement for controlling the electromagnetic assembJies, the switching arrangement being configured to cause the stator poles to magnetically interact with the rotor poles within a predetermined frequency range. Controllers for electric motors are well known and since they are not a feature of the invention, they are not described herein.

The rotor poles may be formed from permanent magnets exploiting the Halbach structure, or any other structure that can be interact with the stator to causes the rotor to rotate around the motor axis.

The rotor may be built from two or more magnetic discs, each formed from a permanent magnet or any other material or structure capable of generating the required electromagnetic field to enable the machine to rotate.

Foils may be used in the stator structure to replace the magnetically rigid cores of the winding thereby reducing the mass of the stator as well as manufacturing costs.

The structure of the device may be an Axial Flux Permanent Magnet (AFPM) or any other type of motor or generator or a regenerative device; wherein the rotor is made from two or more discs, the stator is made from one or more discs in accordance to the number of the rotor discs and the stator core is disposed between two rotor discs.

Alternatively, the structure of the machine can be a Radial Flux Permanent Magnet (RFPM) or any other type of motor or generator or a regenerative device; wherein the rotor is made from two or more cylindrical discs and the stator comprises one or more cylindrical stator discs, each being disposed between an adjacent pair of cylindrical rotor discs, which are mutually coupled at one end to form a shell around the stator.

Alternatively, the machine may be an axial flux induction motor, or any other axial flux type of motor or generator or regenerative device; wherein the stator is made from two or more discs and the rotor comprises one or more rotor discs, each being disposed between an adjacent pair of stator discs. When configured to operate as a motor, the stator generates the required variable magnetic flux that causes the intermediate rotor disc to rotate around the axis.

-iS Alternatively, the machine may be a radial flux induction motor or any other radial flux type of motor or generator or a regenerative device; wherein the stator is made from two or more cylindrical discs and the rotor comprises one or more cylindrical discs, each being disposed between an adjacent pair of stator cylindrical discs. When configured to operate as a motor, the stator generates the required variable magnetic flux that causes the intermediate rotor disc to rotate around the axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following description of non-limiting embodiments taken in conjunction with the appended drawings in which: Figs. la and lb are detailed schematic views of a known per se single conductor coil suitable for a single pole in a single phase of the stator in a multi-phase machine according to the invention; Figs. 2a, 2b and 2c are schematic representations showing successive stages in stacking three coils together to form a unitary three-phase coil arrangement according to an embodiment of the invention; Fig. 3a, 3b and 3c show partial interconnection of stator coils for a three-phase axial flux machine according to an embodiment of the invention; Fig. 4 is a detailed view showing partial construction of a single phase of the stator by interconnecting the coils shown in Fig. la; s Fig. 5 is a detailed view depicting complete construction of a single phase coil in the stator shown in Fig. 4; Fig. 6 shows a detail of an axial flux induction motor according to an embodiment of the invention; Fig. 7 shows a detail of a rotor used in an axial flux induction motor; Fig. 8 shows schematically a radial flux induction motor having a squirrel cage rotor surrounded by stator coils in accordance with another embodiment of the invention; Fig. 9 shows schematically a detail of a squirrel cage rotor of the machine shown in Fig. 8; Figs. lOa and lOb show partial interconnection of stator coils for a two-phase axial flux machine according to an embodiment of the invention; Figs. 11 a and 11 b show partial interconnection of stator coils for a five-phase axial flux machine according to an embodiment of the invention; and Fig. 12 shows a stator coil according to an embodiment of the invention formed of mutually overlapping planar coil slices.

DESCRIPTION OF THE INVENTION

In the following description of some embodiments, identical components that appear in more than one figure or that share similar functionality will be referenced by identical reference symbols.

Figs. 1 a and 1 b are detailed schematic views of a single conductor coil 10 for a single phase and pole of an electrical machine. The coil 10 comprises multiple coil windings formed of a generally flat conductive strip 11 such as copper or aluminum, a first end 12 of which is wound around a second end 13 to form a looped structure of generally trapezoid cross-section having arcuate upper and lower limbs 14 and 15, respectively. The first end 12 thus forms an outermost turn of the coil 10 and is bent double so as to form an arm 16, which projects away from the coil and serves to contact the second end 13 of an adjacent coil.

Small pieces of ferromagnetic material 17 are disposed between adjacent turns of each coil.

Figs. 2a, 2b and 2c are schematic representations showing successive s stages in stacking three coils ba, lOb and lOc together to form a unitary three-phase coil arrangement. The coil I Oa corresponds to the coil 10 in Fig. 1 a, but for ease of description the conductive strip 11 is shown lightly shaded, In Fig! 2b, the coil lOb is shown in a slightly darker grey shade, while in Fig. 2c, the coil lOc is shown in an even darker shade, i.e. black thereby enabling visual discrimination between the three coils. Fig. 2b shows how the coils bOa and lOb are stacked in a staggered relationship while leaving an empty area in the hollow core of the first coil I Oa into which the third coil is now inserted as shown in Fig. 2c. Clearly in the more trivial case of a 2-phase machine, the shape and dimension of the windings in each coil will be the same as that of the hollow core of each coil so that the windings of one coil fit exactly into the hollow core of another. In general for an N-phase machine, the windings in each coil will be shaped so that N-i coil windings fit exactly into the hollow core of the first coil, while taking care to ensure that the coils do not short each other. This is ensured by proper insulation of the coils, such as inserUng them into epoxy resin and allowing them to dry.

It thus emerges that in general the hollow core of the first coil lOa is dimensioned to accommodate therein N-i remaining coils in a staggered arrangement without mutual shorting between two or more coils.

In order to ensure a mechanically balanced multi-phase coil arrangement for more than two phases, alternate phase coils may be mounted on opposite sides of the first coil so a form a symmetrical configuration without derogating from the above relationship.

Fig. 3a is a detailed schematic view of a 3-phase axial flux stator coil 20.

The stator coil includes three separate interlocking coils 1 Oa, lOb and 1 Oc forming respective 3-phase windings, between the conductors of which are so disposed small pieces ferromagnetic material 17, which may include powdered ferromagnetic material. In such an embodiment the coils 1 Ob and 1 Oc are shaped as shown in Fig. 3b so as to have a stepped inner portion 21. This allows the coils 1 Ob and ICc to be mounted on opposite sides of the first coil I Oa that is substantially straight, with the respective stepped inner portions of the opposing coils I Ob and 1Cc being accommodated within the hollow of the first coil 1Cc. This ensures that opposing side surfaces of the coil arrangement remain substantially planar as shown in Fig. 3c. In fact, as will become clear from the following detailed description of specific embodiments, for a coil arrangement having more than three phases, in order to preserve near planarity of opposing surfaces of the coil arrangement, the depth of the stepped portions of each successive pair of phase coils must be increased so as to be accommodated within the recessed -to hollow of the preceding pair of phase coils. Such a 3-phase coil structure can be implemented in a permanent magnet motor (AFPM), an induction motor or in any other axial flux type of motor or generator or any other regenerative device.

Figs. 4 and 5 are detailed views of a single phase of a stator coil 25 formed of a plurality of juxtaposed coils 10 each forming a segment of a circle of -is which intermediate coils are electrically connected by virtue of mechanical contact of the opposite ends 12, 13 of adjacent coils. In practice, the adjoining ends of adjacent coils are welded or otherwise connected to form a secure joint of negligible resistance. As shown in Fig. 5 the first and last winding of the stator coil have respective ends 26, 27 that are not connected to an adjacent coil, and these form feed points for feeding current to one of the phases in the stator of the electric machine. The machine can be a motor or a generator or a regenerative device. In all cases, small pieces of ferromagnetic material 17 are disposed between the respective flat surfaces of adjacent windings in each coil.

Adjacent loops of each coil are insulated from one another so as to prevent electrical contact between adjacent coil windings. This may be achieved by pre-coating the windings with an insulating material, thus allowing the coil to be wound from pliable strip material. When using heavy gauge metal strip, the coil may be wound to form small air gaps between adjacent coil windings into which the ferromagnefic material 17 is disposed prior to immersing the complete coil winding into epoxy, so as to fill any remaining gaps and provide the required insulation between adjacent coil windings.

Fig! 6 shows a detail of an axial flux induction motor 30 according to an embodiment of the invention having a pair of N-phase stator coils 10 as shown in Fig. 3. The stator coils 10 conforming to the arrangement described above with reference to Figs. 2 to 5 are mounted on opposite sides of a rotor 31 comprising an annular slotted cage which rotates between the stator coils 10. If desired, more than one rotor may be mounted on a common shaft 32 (shown schematically in Figs. 7 and 8), each rotor being mounted between respective stator coils. Each pair of N-phase stator coils 10 generates the required varying magnetic flux that causes the intermediate rotor to rotate around the motor axis.

As shown in Fig. 7, the rotor 31 of the axial flux induction motor shown in Fig. 6 is in the form of a cage comprising inner and outer rims 33 connected by radial spokes 47 formed of electrically conductive material and between whose gaps are disposed small "slices" of ferromagnetic material 17. Each slice of ferro-magnetic material may be a stack of several ferromagnetic foils or slices.

Fig. 8 shows schematically a multi-phase radial flux induction motor 40 in accordance with another embodiment of the invention whose stator is constructed from a pair of annular cylindrical stator elements 43 and 44 that are commonly fixed to a motor shaft 32 and which surround the rotor 45. The two stator elements 43 and 44 may be assembled from permanent magnetic segments or from any other material or structure capable of generating the required magnetic flux to cause the rotor 45 to rotate with the shaft within the surrounding stator elements 43 and 44. The stator elements 43 and 44 may conform to the permanent magnet in a Halbach structure or to any other suitable structure, known in the art.

Fig. 9 shows schematically a detail of the annular squirrel cage rotor 45.

The squirrel cage rotor 45 has a pair of opposing annular electrically conductive end faces 46 between which and toward respective peripheries thereof are coupled spaced apart electrically conductive spokes 47 forming intermediate gaps. Ferromagnetic material 17 may be disposed between adjacent bars of the rotor cage 45.

Most of the machines described above are three-phase machines.

However, the coil arrangements according to the invention are equally suitable for use with multiple phase machines having two or more phases.

Fig. 1 Oa is a perspective view showing construction of a 2-phase axial flux stator coil 50 and Fig. I Sb is an exploded view showing its construction. The stator 50 coil includes two separate interlocking coils iDa and lOb each constructed according to the embodiment described above with reference to Figs. 1 to 3 and forming respective 2-phase windings, between the conductors of which are disposed small pieces ferromagnetic material 17. ln such an embodiment the coil 1 Ca (constituting a first coil) is substantially straight and has a hollow core, which is dimensioned to accommodate therein the coil lOb which has a stepped inner portion 21. In Fig. 13b, the stack of ferromagnetic material 17 is shown intermediate the two coils showing that when the two coils are mounted in inter-locking relationship, the ferromagnetic material 17 extends across the complete is width of the coil arrangement. This 2-phase axial flux stator structure can be implemented in a permanent magnet motor (AFPM), an induction motor or in any other axial flux type of motor or generator or any other regenerative device.

Fig. 11 a is a detailed schematic view of a 5-phase axial flux stator coil 55 and Fig. 11 b is an exploded view showing its construction. The stator coil 55 includes five separate interlocking coils comprising a first coil 1 Ca, a first pair of coils {lOb, lOc} and a second pair of coils {lOd, lOe}. The coils are constructed according to the embodiment described above with reference to Figs. Sa and 3b and form respective 5-phase windings, between the conductors of which are disposed small pieces ferromagnetic material 17. In such an embodiment the first coil 1 Ca is substantially straight and has a hollow core, which is dimensioned to accommodate therein the remaining coils 1 Ob-1 Ce, each of which has a stepped inner portion 21 that allows the coils lOb-ICe to be mounted substantially flush with the coil 1 Ca. As noted above, the depth of the stepped inner portions of the second pair of coils 1 Od, 1 Ce is greater than that of the first pair of coils 1 Ob, I Cc, so so that the respective surfaces of all the remaining N-i coils are substantially co-planar. This 5-phase axial flux stator structure can be implemented in a permanent magnet motor (AFPM), an induction motor or in any other axial flux type of motor or generator or any other regenerative device.

Fig. 12 is a detailed schematic view of an alternative N-phase stator that may be implemented as a PCB board or any type of thin mutually insulated coil layers that are stacked to create an N-phase coil structure. Between each one or more conductor ferromagnetic material is inserted (not shown in the figure). Such a coil arrangement is suitable for a machine having two or more phases (i.e. N>1). Each phase coil 10 can be built in a single small thin layer or of many small thin layers BOa, 60b. During manufacture, each layer is insulated and electrical io connection between the coil slices is effected using vias or jumpers or any other type of connection through the coil stack to connect between the layers and create the required coil structure. This allows a motor/generator to be constructed with many layers wherein small pieces of ferromagnetic material 17 are inserted between one or more conductors as shown in Fig. 3a.

is It will be appreciated that embodiments have been described by way of example and modifications may be made without departing from the scope of the invention as defined by the claims. For example, while in the embodiments as described, ferromagnetic material is disposed between the air gaps of all coil windings, it will be understood that not all air gaps need be filled with ferro-magnetic material to benefit from the construction of the invention.

Likewise, although only specific combinations of machine have been described, it will be appreciated that electric motors and generators are merely alternative ways to configure an electrical machine. Consequently, embodiments that have been described with reference to electric motors can equally well be configured as electrical generators and vice versa.

It will likewise be understood that the coil arrangement according to the invention can be implemented in either the stator or the rotor in all embodiments.

It will also be understood that multiple stators and rotors can be mounted in cascade in order to increase the power rating of the machine.