Electrical machines with isolated rotors

Abstract

The electric machine (1), which is a modulated pole machine operated by switching magnetic flux, includes a rotor (10), a stator (20), and windings (30). The rotor and stator have respective sections (12, 22) interleaved with each other through five or more air gaps. At least two different sections each contain winding loops from the same phase winding. At least one of the sections that is part of the rotor is an isolated rotor section that includes a non-conductive structural material.

Description

[Technical Field]

[0001] The present invention relates generally to electric machines, and more particularly to modulated pole machines. [Background technology]

[0002] The concept of an electric machine is well known, and the first types of electric machines, such as induction machines and synchronous machines, developed in the late 19th century, are still very important in industry today. Electric machines generally include one moving part, typically but not limited to a rotor or translating mechanism, and a second part, typically but not limited to a stator. These parts are separated by an air gap that separates the moving part and the second part. At least one of the parts, typically the stator, also has electrical windings capable of conducting electric current.

[0003] A characteristic of electric machines is that they have a low force or torque density compared to mechanical systems such as gearboxes, hydraulic systems, and pneumatic systems, but a high power density because they can operate at high speeds. A power density of 1 kW / kg is a typical figure for an electric motor.

[0004] A feature of most electric machines is also that resistive power losses, which often constitute the majority of losses in electric machines, are independent of the air-gap speed v if eddy currents in the windings are neglected. However, when counted as a percentage of total power, resistive power losses are proportional to 1 / v because total power is proportional to v. Thus, typical electric machines have high efficiency at high speeds, typically in the 10-100 m / s range, with efficiencies in the 90-98% range being common. At low speeds, e.g., less than 5 m / s, electric machines typically have lower efficiencies.

[0005] Resistive losses also typically cause thermal problems within electric machines, limiting torque and force density, as well as power density for operations longer than a few seconds.

[0006] Due to their low power or torque density and poor low-speed efficiency, electric machines are often used in combination with gearboxes, hydraulic systems, or pneumatic systems in applications requiring high torque or power and low speeds. This allows the electric machine to operate at high speeds and low torque. However, these mechanical systems have certain drawbacks. Mechanical conversion generates additional losses within the system, typically 3-20% depending on the system, and can even be higher at partial loads. Mechanical conversion systems also require more extensive maintenance than the electric machine itself, which can increase overall costs. For example, in wind power generation, maintenance issues in gearboxes have been a continuing major problem over the past 20 years.

[0007] To circumvent the low-speed efficiency and low-force density problems, several different machine types have been proposed and developed, belonging to a family of machines known as modulated pole machines (MPMs) or variable reluctance machines (VRMs) (the variable reluctance permanent magnet machine (VRPM) is a further specialization). Different variants of these machine types, such as vernier machines (VMs), vernier hybrid machines (VHMs), and transverse-flux machines (TFMs), implement a geometric effect known as magnetic gearing, which significantly lowers winding resistance by making the windings shorter and thicker. This is achieved by arranging the geometry so that the magnetic flux from several adjacent poles results in a significant net flux in the same direction, and so that the magnetic flux from these poles switches direction when the moving part, i.e., the translation mechanism or rotor, is moved one pole length.

[0008] These machines also develop higher shear stresses than other machines, where shear stress is defined as the useful shear force per unit air gap area. However, they generally do not significantly increase the amount of air gap area packed per unit volume compared to standard machines, so the power density of these machines is increased, but only slightly. Known problems with these machine types are high leakage flux and low power factor at full load. Thus, they cannot have both a high power factor and very high shear stresses. They have been proposed for wind power generation, but they have not achieved wide market penetration due to these drawbacks.

[0009] One type of TFM machine has been proposed in references [1-4]. This machine has the advantage of packing a significant air gap area per unit volume. However, this machine appears like a two-part transformer, with up to two bulk coils per phase, with the coils located away from the air gap. Unfortunately, this design also has some minor drawbacks. The proposed design results in a large leakage flux, which results in a low power factor. It also has a large clamping normal magnetic force, which requires a strong mechanical structure to hold the core. This is due to the fact that the coils are wound only around two structures, and these two structures are located away from some of the air gap.

[0010] A problem with prior art electric machines is that in low speed applications and where high force or torque density is required, current solutions are unable to reach very high torque or force densities, and most high torque density machines have a low power factor at full load, which often results in large, expensive direct drive machines with substantial losses. Summary of the Invention

[0011] Therefore, a general objective of the presented technology is to provide an electric machine with improved overall torque or power density and increased low speed efficiency.

[0012] The above object is achieved by a device according to the independent claims. Preferred embodiments are defined in the dependent claims.

[0013] Generally speaking, in a first aspect, a rotating electric machine that is a modulated pole machine that operates by switching magnetic flux includes a rotor, a stator, and a winding. The winding includes at least two phase windings. The rotor and stator include respective sections interleaved with each other through five or more air gaps, which are parallel to the direction of rotation, which is the direction of movement of the rotor relative to the stator in the air gaps. At least two different sections, preferably at least three different sections, and most preferably at least four different sections, each include winding loops from the same phase winding. At least one of the sections that is part of the rotor is an isolated rotor section that includes a non-conductive structural material.

[0014] In a second aspect, a system includes an electric machine according to the first aspect, the system being a renewable energy conversion system, a wind power plant, a tidal power plant, an ocean wave power plant, an electric ship propulsion system, a gearless motor, an electric vehicle, a direct drive system, or a high force density actuator.

[0015] One advantage of the proposed technology is that it increases the force or torque density of the machine, increasing its efficiency, especially at low speeds. Other advantages will be understood upon reading the detailed description.

[0016] The present invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which: [Brief explanation of the drawings]

[0017] [Figure 1A]FIG. 1A illustrates an embodiment of a rotating electrical machine that operates by switching magnetic flux. [Figure 1B] FIG. 1B is a cross-sectional view of the embodiment of FIG. 1A. [Figure 1C] 1C-1D are schematic diagrams of one embodiment of a stator. [Figure 1D] 1C-1D are schematic diagrams of one embodiment of a stator. [Figure 1E] 1E-1F are schematic diagrams of one embodiment of a rotor. [Figure 1F] 1E-1F are schematic diagrams of one embodiment of a rotor. [Figure 1G] 1G-1H are schematic diagrams of embodiments of the geometric and magnetic relationships between magnetic structures in the rotor and stator. [Figure 1H] 1G-1H are schematic diagrams of embodiments of the geometric and magnetic relationships between magnetic structures in the rotor and stator. [Figure 2A] 2A-2D are schematic diagrams of embodiments of the geometric relationship between the rotor and the stator. [Figure 2B] 2A-2D are schematic diagrams of embodiments of the geometric relationship between the rotor and the stator. [Figure 2C] 2A-2D are schematic diagrams of embodiments of the geometric relationship between the rotor and the stator. [Figure 2D] 2A-2D are schematic diagrams of embodiments of the geometric relationship between the rotor and the stator. [Figure 3] FIG. 3 is a schematic diagram of the magnetic flux in the air gap. [Figure 4] FIG. 4 is a diagram showing an example of the changing air gap magnetic flux. [Figure 5A] FIG. 5A is a schematic diagram of a cross section of one embodiment of a stator magnetic structure and associated winding loops. [Figure 5B] FIG. 5B illustrates how the enclosed magnetic structure can be securely fastened to the windings by using splines. [Figure 5C]FIG. 5C illustrates how the enclosed magnetic structure can be securely fastened to the windings by using a structure that overlaps the windings. [Figure 6] FIG. 6 is a schematic diagram of one embodiment of the geometric relationship of first and second magnetic structures utilizing surface mounted permanent magnets. [Figure 7] FIG. 7 is a schematic diagram of one embodiment of the geometric relationship of the first and second magnetic structures in a switched reluctance machine. [Figure 8] FIG. 8 is a schematic diagram of a portion of one embodiment of a modulated pole machine with poloidal flux. [Figure 9] FIG. 9 is a schematic diagram, with portions cut away, of the rotor and stator structure and portions of the windings of a modulated pole machine with poloidal flux. [Figure 10] FIG. 10 is a schematic diagram, with a portion cut away, of a portion of another embodiment of a modulated pole machine having poloidal flux and toroidal windings. [Figure 11] FIG. 11 illustrates an embodiment in which each phase in the stator disk has its own magnetic return path, independent of the other phases. [Figure 12] FIG. 12 illustrates an embodiment similar to that shown in FIG. 1A, but in which the magnetic topology is switched between the rotor and the stator. [Figure 13A] 13A-13B are diagrams illustrating two embodiments in which the magnetic flux is primarily radial. [Figure 13B] 13A-13B are diagrams illustrating two embodiments in which the magnetic flux is primarily radial. DETAILED DESCRIPTION OF THE INVENTION

[0018] Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

[0019] The technology presented here provides an elegant solution to both the general torque or power density problem and the low-speed efficiency problem of electric machines by having extremely high torque or power density, very high efficiency, and maintaining a satisfactory power factor even at low speeds. This is preferably achieved by considering three different aspects, and these concepts provide the framework within which the design and geometric features must follow.

[0020] Winding resistance is often a major drawback. To achieve a much lower winding resistance, the technology presented here implements so-called magnet gearing. This concept means that the winding is wound around many poles, rather than between each individual pole. Typically, the entire phase is enclosed within a simple loop. This allows the winding to be several times shorter than in standard machines. At the same time, the winding can also be several times thicker, which makes the winding resistance many times smaller than in standard machines. By such measures, the winding resistance can be reduced by approximately 1 / 100 to 1 / 5, depending on the geometry and size. This also significantly reduces thermal issues.

[0021] Another concept to consider is increasing the number of air gaps within as small a volume as possible. In other words, since machine power is developed within the air gaps, the goal is to increase the total air gap area in a given machine volume. The techniques presented herein implement a geometry that magnetically connects many air gaps in series, tightly packed together in a geometry that closely resembles a magnetically closed loop. This is preferably achieved without unnecessarily long magnetic field lines within a block of magnetic material, such as iron. The geometries presented herein achieve this by reducing any passive return paths in magnetic material for magnetic flux. Thus, many times larger air gap areas can be packed per unit volume in the machines presented herein compared to standard electric machines. Furthermore, this is accomplished without using excessive amounts of permanent magnets.

[0022] Many embodiments of the present invention involve permanent magnets. Mostly, neodymium-iron-boron magnets are used due to their superior performance. Neodymium-containing magnets, often simply called neodymium magnets, have very high remanence and coercivity, resulting in very force-dense and efficient electric machines. However, these magnets contain rare earth elements, which are scarce and expensive. An alternative is to use ferrite magnets instead. While the performance of these magnets is significantly inferior in almost every aspect to neodymium-iron-boron magnets, they do not contain exotic materials, they are very low cost, they do not conduct current, thereby eliminating eddy current problems, and they are not heat-sensitive. Thus, in some applications, it is beneficial to use ferrite magnets instead of neodymium-iron-boron magnets, especially within magnetic flux-concentrating structures.

[0023] The large number of air gaps, combined with the reduced resistance in the windings, also allows for significantly higher power loads in the electric machine. This, combined with the reduced resistance in the windings, also allows for significantly higher power loads in the electric machine. This means that the shear stress, i.e., the useful force per unit area developed in the air gaps, is two to four times higher than in a standard machine. Up to 100 kN / m 2 Even forces per unit area of ​​1000 psi are achievable. The gain in shear stress is even greater compared to standard machines when many air gaps are packed closely together due to magnetic gearing, since standard machines, such as axial flux machines, have unfavorable scaling in this regard. This, combined with the considerable increase in air gap area per unit volume or weight, gives the technology presented here force or torque densities many times greater than those for standard machines, typically 5 to 25 times greater.

[0024] Another advantage of this geometry is that it can be preferably arranged so that normal forces on the magnetic material in most of the air gap can, at least ideally, be locally eliminated, thereby significantly reducing the need for heavy and bulky structural materials. Elimination of normal forces on the magnetic material is typically implemented in prior art electric machines, but typically in a global sense. This therefore requires internal structures that carry normal forces from one side of the machine to the other. However, the normal force elimination presented here in a local sense is highly advantageous. The need for robust internal structures is significantly reduced by the techniques presented here.

[0025] An additional benefit of some of the preferred embodiments is the elimination of leakage flux. By arranging the phase windings in a distributed manner in at least two, but preferably more, stator sections, the entire winding for a phase resembles a closed or nearly closed coil geometry. This geometry can be a racetrack coil or similar. With such a geometry, leakage flux can be significantly reduced or nearly eliminated. The windings in these machine embodiments are arranged for this purpose in a manner that nearly eliminates overall leakage flux. Thus, the power factor of the machine can be maintained at a reasonable level without reducing shear stresses, reaching a power factor of 0.8 in preferred embodiments. Such a geometric relationship also reduces problems with eddy currents in the windings and machine structure, as well as planar eddy currents in the magnetic steel sheets.

[0026] The present invention relates to a type of electric machine that preferably utilizes geometric effects to significantly increase the machine's power or torque density and increase its efficiency, particularly at low speeds and in preferred cases without sacrificing power factor. The technology presented here has unprecedented performance in low-speed applications such as direct drives and applications where high power or torque density is required, but is not limited to these applications. Preferred applications are wind, tidal, and ocean wave power generation, i.e., renewable energy conversion systems, electric ship propulsion, electric vehicles, gear motor replacements, direct drive applications, and high power density actuators, but the invention is not limited thereto and can be used in many other applications as well.

[0027] Some terms used in this disclosure may require explicit definition.

[0028] An "electric machine" shall be understood to be a machine that, when an electric current is applied, is capable of exerting a force on a movable body, or vice versa. Typically, electric machines are used as generators, motors, or actuators.

[0029] An "air gap" is typically filled with air, but may include any material that is non-magnetic, such as, but not limited to, gas, liquid, plastic, composite material, or plain bearing material such as Teflon.

[0030] "Non-magnetic" shall be interpreted herein as a material having a relative permeability of <50 at a magnetic flux density B of 0.2 Tesla and a material having a residual magnetic flux density of <0.2 Tesla. Additionally, "magnetic" shall be interpreted herein as a material having a relative permeability of ≥50 at a magnetic flux density B of 0.2 Tesla or a residual magnetic flux density of ≥0.2 Tesla.

[0031] Mechanical power is expressed as P=Fv, where F is force and v is velocity.

[0032] "Speed" is defined here as the relative speed between the rotor and the stator. Speed ​​is defined at the respective surfaces of these two parts in the air gap separating them.

[0033] "Non-conductive" here means 10^-5 Ohms at 20 degrees Celsius * shall be interpreted as a material having an electrical resistivity greater than m.

[0034] "Conductivity" here is 10^-5 Ohms at a temperature of 20 degrees Celsius * shall be interpreted as a material having an electrical resistivity less than or equal to m.

[0035] "Material of construction" is defined as any material or part of the machine that does not play a major active role in the magnetic circuit of the electric machine or is a conductive part of the windings.

[0036] "Force" is defined here as the relative force exerted by the current between the rotor and the stator. The force acts at the surface of each of these two parts in the air gap separating them and along the motion, resulting in a shear force at the surface.

[0037] "Normal force" is defined herein as the normal attractive force in the air gap between the rotor and stator.

[0038] A "high magnetic permeability material" is defined in this disclosure as a material that has a relative magnetic permeability greater than 50 at a magnetic flux density greater than 0.2 Tesla.

[0039] The geometry of the technology presented here is arranged to implement magnetic gearing so that the magnetic flux is unidirectional or nearly unidirectional inside a simple winding loop. This winding loop is typically a rectangular-like winding loop that encircles the magnetic flux across at least three magnetic poles of the same polarity, as discussed further below. Note that this is not the same as distributed windings in a synchronous electric machine, where the magnetic flux is not unidirectional.

[0040] Thus, the present invention belongs to a group of electric machines that implement magnetic gearing, such as vernier machines (VMs), vernier hybrid machines (VHMs), transverse flux machines (TFMs), and switched reluctance machines (SRMs). These machines are characterized by a toothed structure of magnetic material that modulates the magnetic field during operation. Therefore, this group of electric machines is often referred to as modulated pole machines (MPMs) in the literature [5, 6], and this term will be used later in this document. They are also sometimes referred to as variable reluctance (VR) machines, or, in the case of permanent magnet machines, as variable reluctance permanent magnet machines (VRPMs), which are essentially broad terms. These machines generally achieve low resistance, but do not reach the same high force or torque densities as the present invention, since they do not magnetically connect many air gaps in series, and therefore do not pack as large an air gap area per unit volume as the present invention, but rather up to several times smaller. Also, these machines do not avoid leakage flux to the same extent as the present invention, and thus have more problems with eddy currents and low power factor. These machines also do not cancel magnetic normal forces in a localized sense to the same extent as the technology presented here. Thus, they require more structural material for the same amount of torque, which makes them heavier and more expensive.

[0041] An axial-flux synchronous electric machine (AFM) is a well-known synchronous machine in which the magnetic flux is arranged axially. It has been suggested in some cases that an axial-flux machine can operate with many air gaps magnetically connected in series, which can increase its torque density. However, because the AFM does not implement magnetic gearing, it does not have nearly as low a winding resistance as the present invention, and therefore cannot generate the same shear stress in the air gap, and therefore cannot achieve both high efficiency and high torque density. Furthermore, the AFM cannot pack as much air-gap area per unit volume as the present invention because the winding resistance for the AFM scales unfavorably compared to the present invention when the magnetic poles are shortened. These described features give the present invention significantly better performance, in terms of a combination of efficiency and force or torque density, than any electric machine that does not implement magnetic gearing, including iron-core or air-core synchronous electric machines with or without permanent magnets, induction machines, and synchronous reluctance machines, or a combination thereof.

[0042] Common types of synchronous electric machines that do not implement magnetic gearing use either concentrated or distributed windings. With concentrated windings, each winding usually wraps around the flux from only one pole, or with a wave-like winding that spans the air gap and surrounds the flux from every other pole to surround poles of the same polarity. In synchronous machines with distributed windings, windings from different phases overlap to produce a reasonably functioning machine, which causes large winding ends and windings to cross over each other. Although a distributed winding loop surrounds the flux from many poles, it never surrounds a total flux greater than the flux from one individual pole. This is because the excess of the number of surrounded poles of one polarity compared to the number of poles of the other polarity is never greater than one. A feature of the technology presented here is that the windings enclose an enclosed magnetic structure that carries magnetic flux from multiple poles, preferably with a simple winding loop that encloses the magnetic flux from five or more adjacent poles. Due to magnetic gearing, the net magnetic flux through the windings is greater than the magnetic flux from one individual pole, or preferably greater than twice the magnetic flux from one individual pole. In other words, the total magnetic flux is greater than the magnetic flux from two individual poles of the same polarity. This is because the modulated pole geometry that results in magnetic gearing weakens the magnetic flux from poles of one polarity and increases the magnetic flux from poles of the other polarity, resulting in a larger net magnetic flux. If a geometry is selected that results in a net magnetic flux through the winding loop that is less than the magnetic flux from one individual pole, there is little value in implementing magnetic gearing.

[0043] Another feature of the technology presented here is that the windings are significantly shorter for a given induced voltage than in standard machines. In conventional electric machines that do not implement magnetic gearing and do not have distributed windings, the windings in a winding loop span an air-gap area perpendicular to the direction of rotation that is twice the number of poles of the same polarity, n, that the winding encompasses. This is because the winding must wrap around each pole individually to avoid capturing magnetic flux of opposite polarity in adjacent poles. Due to the presence of winding ends, the length of the winding loop is always longer than 2 × n × d, where d is the average width of the magnetically active portion of the air gap taken parallel to the air gap and perpendicular to the direction of rotation. To have any reasonable gain using magnetic gearing, the windings must be shorter than this, i.e., shorter than 2 × n × d, and preferably significantly shorter than n × d. Thus, it is a feature of magnetic gearing that a winding loop encloses magnetic flux from n magnetic poles of the same polarity, n being greater than 2, preferably n being greater than 4, and more preferably n being greater than 6, and that the winding loop encloses a total magnetic flux greater than the magnetic flux from one individual pole, preferably greater than twice the magnetic flux from one individual pole, and that the winding loop length is less than 2 x n x d, preferably less than n x d, and that the air gap width distance d is the average width of the magnetically active portion of the air gap taken in a direction parallel to the air gap and perpendicular to the direction of rotation, and that the magnetic poles are provided on at least one of the rotor and stator. A further feature of the technology provided herein is that different phases and windings of an electric machine may be localized in different parts of the machine to form several one-phase machines that are more or less mechanically connected. This also means that windings from different phases generally do not overlap, i.e., poles surrounded by winding loops from one phase winding are preferably not surrounded by winding loops belonging to another phase. This differs from synchronous machines with distributed windings, where the phases are usually twisted together. Of course, there may inevitably be some overlap, resulting in partial overlap of windings from different phases.This reduces efficiency and power density and complicates the structure, but may play a role in reducing cogging torque. It is currently believed that at least 30% of the magnetic flux from a pole encompassed by one phase winding loop must be outside any other winding loops belonging to other phases. In other words, at least 30% of the magnetic flux from a pole encompassed by one phase winding loop should not be encompassed by any other winding loops belonging to other phases. More precisely, the present invention is characterized in that at least one winding loop, the first winding loop, encompasses magnetic flux from at least five poles, and at least 30%, preferably at least 50%, more preferably at least 70%, even more preferably at least 90%, and most preferably 100% of the magnetic flux from the at least five poles is outside all other winding loops belonging to other phases and located in the same area as the first winding loop.

[0044] However, magnetic flux from a pole in one area may also pass through the same area elsewhere in another pole, since in embodiments related to the present invention the magnetic flux forms a closed loop. The interpretation of magnetic flux from at least five poles is intended in this context to mean the magnetic flux in the air gap at that very pole, and not at other poles to which the magnetic flux may have its return path.

[0045] Rotors of electric machines are typically made of metal, a conductive material. Metals have many benefits, such as high mechanical strength and rigidity and resistance to mechanical cold flow. However, there is also a risk that eddy and circulating currents within the rotor structure will cause power losses and reduce the efficiency of the machine. This problem is more pronounced in the present invention because the present invention is a flux-switching machine, which typically has short pole lengths and therefore high electrical frequencies compared to the speed in the air gap. Therefore, it is beneficial for the rotor to include electrical isolation material within its structure, which can be used to avoid or reduce circulating and eddy currents within the structure. While the rotor can be made almost entirely of electrical isolation material, it can also have only a smaller portion of electrical isolation material strategically placed near the air gap. In other words, it is beneficial for at least one section of the rotor to be an isolated rotor section that includes a non-conductive structural material. To avoid circulating currents within the structure, it is preferred that at least one, and preferably all, closed loops of structural material surrounding the permeable material in the air gap in at least one rotor section have an electrical resistance greater than 0.05 ohms.

[0046] A phase winding should be interpreted as the entire winding belonging to the same phase, regardless of whether the winding is separated into several windings connected in parallel or further separated into several windings connected to different transformers. Also, when determining whether windings in different stator sections belong to the same phase, they should be considered to belong to the same phase even if the voltages in the windings are displaced by several electrical degrees relative to each other, since the magnetic fields will anyway be connected in series for at least two stator sections. A practical limit may be set here at a difference of 30 electrical degrees, although configurations with a difference of close to or equal to zero electrical degrees are preferred.

[0047] FIG. 1A illustrates one embodiment of an electric machine 1 that operates by switching magnetic flux, where the magnetic flux is primarily axial. This embodiment is a three-phase machine, with different phases 2A, 2B, and 2C positioned behind each other along the direction of rotation 4. Thus, in this embodiment, the winding 30 includes at least two phase windings 31. Each phase essentially operates independently of the other, but in this embodiment, magnetic flux from one phase has a return path in the two other phases. The phase structures are mechanically connected to each other, resulting in a fairly smooth resultant with moderate cogging. The electric machine 1 includes a rotor 10, which in this embodiment is divided into four rotor sections 12, two inner rotor sections 12A, and two end cap sections 12B. The electric machine 1 further includes a winding 30 having several loops 32. In this embodiment, inside the loops 32 is an enclosed magnetic structure that is firmly fixed to the winding. The winding loops 32 encircle at least five adjacent poles, in this particular embodiment, 26 adjacent poles, and, due to magnetic gearing effects, encircle significantly more magnetic flux than from one or two individual poles. The stator 20, in this embodiment, is divided into three stator sections 22, each with winding loops from the same phase winding. In other words, windings from the same phase are present in all stator sections 22. The machine structure has been removed so that the rotor and stators 10, 20, and windings 30 can be seen.

[0048] A "zone" in this disclosure refers to a mechanical component having, at each portion, an elongation in a first and a second direction, the second direction being different from the first direction and typically significantly greater, typically at least an order of magnitude, than the elongation in a third direction perpendicular to the first and second directions. This third direction is also referred to as the axial direction 15 associated with the zone. Thus, a zone is, in most cases, essentially flat when viewed as a whole, although it may be curved, typically into a circular cross-sectional shape or, in some embodiments, a slightly wedge-shaped shape. However, the surface of a zone may include non-flat components, such as protrusions or recesses. As further described below, a zone may also be composed of different parts and / or materials.

[0049] The rotor and stator sections 12, 22 of the rotor and stator 10, 20 are positioned opposite each other via an air gap 40. The air gap 40 is parallel to the direction of rotation 4, i.e., the magnetic flux passing through the air gap is essentially perpendicular to the direction of rotation 4. The rotor 10 and stator 20 have their respective rotor and stator sections 12, 22 interleaved with each other via the air gap 40 along the axial direction 15. In other words, when passing along the axial direction, the rotor section 12 of the rotor 10 is followed by the stator section 22 of the stator 20, separated by the air gap 40, except on one side of the end cap section 12B. Similarly, when passing along the axial direction, the stator section 22 of the stator 20 is followed by the rotor section 12 of the rotor 10, separated by the air gap 40. Thus, between each pair of adjacent stator sections 22 of the stator there is an inner rotor section 12A of the rotor 10, and similarly between each pair of adjacent rotor sections 12 of the rotor 10 there is a stator section 22 of the stator 20. An outer rotor section or end cap 12B is placed at the axial end of the machine and closes the magnetic circuit.

[0050] Each inner rotor and stator section 12A, 22 may thus be defined as the portion of the rotor and stator 10, 20 located axially between the rotor and stator section surfaces facing two consecutive ones of the air gaps 40. The outer rotor section 12B may be defined as the axially outermost rotor section facing one outermost air gap and having no other rotor section on the same side of the outermost air gap.

[0051] 1B shows a cross-sectional view of the electric machine 1 of FIG. 1A. Here, the rotor section 12 and the stator section 22 are more clearly shown. Here, it can be seen that the stator section 22 of the stator 20 is located axially between the stator section surfaces 24, 26 that face two successive ones of the air gaps 40. Also, the inner rotor section 12A of the rotor 10 is located axially between the rotor section surfaces 14, 16 that face two successive ones of the air gaps 40. The outer rotor section or end cap 12B is located at the axial end of the machine on one side of the air gap, with all other rotor and stator sections located on the other side of the air gap.

[0052] Furthermore, for each inner rotor and stator section 12A, 22 of the rotor and stator 10, 20, the magnetic field lines pass through the magnetic material between the rotor and stator section surfaces 14, 16, 24, 26. This means that many air gaps 40 are magnetically connected in series in this embodiment 6. The magnetic loop is closed by the end cap, the outer rotor section 12B. The air gaps 40 are packed relatively closely together, and there are no very long magnetic field lines within the block of magnetic material.

[0053] These properties can be further enhanced by further increasing the number of interleaved rotor and stator sections, and thus the number of air gaps. Currently, it is believed that five or more air gaps must be present to achieve significant benefits. More pronounced benefits are achieved using seven or more air gaps. Even more preferably, nine or more air gaps are provided, and for truly high-power or high-torque-density machines, eleven or more air gaps are preferably provided. Two of these sections are typically end sections, either rotor sections or stator sections, which have no air gaps on two sides, but only on one side, and close the magnetic circuit of the electric machine.

[0054] In this embodiment, there is a permanent magnet, so it is a modulated pole machine that includes a permanent magnet that operates by switching magnetic flux.

[0055] In this embodiment, there are three phases in each stator section 22, and thus winding loops from three phases. For mechanical reasons, it is preferable to have forces that vary only slightly with position within the stator and rotor sections, as vibration and fatigue problems can otherwise occur. To achieve this, two or more phases are required within a section. Having three or more phases within a section is highly desirable because the sum of the magnetic flux in all phases can then ideally be zero while maintaining a smooth force. However, the more phases there are in a section, the smoother the forces will be, and four or more phases may be beneficial if the space requirements and additional cost of having additional phases do not offset the benefits. For larger machines, seven or more phases may be beneficial, and for very large machines, ten or more phases may be the best choice. For bulky machines such as large wind turbines, thirteen or more phases will provide an even better force profile.

[0056] The reduction of force fluctuations in the stator area also applies to the entire machine. Thus, a smoother resultant force can be achieved if the electric machine has four or more phases, and even more so if seven or more phases are applied. For large machines, ten or more phases can be beneficial in this regard, and for even larger machines, thirteen or even sixteen or more phases can be used to provide very low cogging forces. Having many phases also opens up the possibility of shutting down individual phases when a fault occurs while still using the others. Thus, a large number of phases can provide the machine with fault-tolerant characteristics.

[0057] 1A and 1B, there are also various structures of the rotor and stator sections 12, 22 along the direction of rotation 4. This will be discussed in more detail in relation to FIGS. 1C-F.

[0058] FIG. 1C illustrates a portion of one of the stator section surfaces 24 of one embodiment, viewed from the air gap. The stator section 22 of the stator 20 includes, in this embodiment, stacks of permanent magnets 27A, 27B interleaved with blocks of electrical steel sheets 25 or any other high-permeability material referred to as the stator section of high-permeability material 23. The term "stator" is used because this section is provided within the stator 20. The electrical steel sheets 25 typically impede eddy currents. The stator section of high-permeability material 23 conducts magnetic fields well, and because the permanent magnets are positioned with alternating polarity in the direction of rotation 4, every other stator section of high-permeability material 23 presents a north magnetic pole N and the other a south magnetic pole S. The stator section of high-permeability material 23 acts as a flux-concentrating structure. Thus, in this embodiment, the stator 20 presents a north and south permanent magnet pole S in each air gap in the direction of rotation 4.

[0059] The permanent magnets in the above embodiments are therefore arranged in a flux concentrating configuration, in which the magnetic flux from the permanent magnets is conducted, for example by a high magnetic permeability material, into narrow geometric structures that are narrower than the poles of the permanent magnets themselves. This therefore results in the magnetic flux within such narrow structures being higher than the magnetic flux at the very poles of the permanent magnets. The exact form of such structures is within the knowledge of those skilled in the art and will preferably be determined on a design-by-design basis.

[0060] Electrical steel is usually produced with a non-stick coating, and the individual plates are stacked and held together by different fastening methods. However, since the idea involves many small parts, it may be beneficial here to use electrical steel with an adhesive coating. An automatic stamping machine can then produce pre-glued blocks of the desired shape, which simplifies assembly and makes the electrical machine more rigid.

[0061] Another high-permeability material, described for example as an interleaved block with permanent magnets or in other designs using electrical steel sheets as further described below, is soft magnetic composites (SMCs). These materials contain iron particles with an electrically isolating coating that are sintered into the final shape. This differs from electrical steel sheets, which are typically pressed into shape by a die or laser cut and then laminated. SMCs can conduct magnetic flux in all directions without exhibiting any significant eddy currents, but they have higher hysteresis losses than electrical steel sheets.

[0062] The average distance 21 between consecutive poles of the same polarity in the stator 20 is illustrated by a double-headed arrow. In this particular embodiment, all distances between consecutive poles of the same polarity are the same, and therefore so is their average. However, in alternative embodiments, the permanent magnets may be provided somewhat displaced, which means that the distance between consecutive poles of the same polarity may vary somewhat, but there will always be an average.

[0063] In FIG. 1D, the same portion of the stator region 22 as that within FIG. 1C is illustrated radially. Here, the stator region surfaces 24 and 26 can be easily seen. The illustrated path 42 exemplifies one example of how magnetic field lines pass through a magnetic material including the stator portions of the permanent magnets 27A, 27B and the high permeability material 23 between the stator region surfaces 24, 26. The stator region surfaces 24 and 26 are, in other words, magnetically connected to each other.

[0064] Therefore, at least one of the stator regions 22 of the stator 20 includes permanent magnets 27A, 27B arranged to present alternating poles along the surfaces 24, 26 facing the air gap.

[0065] In a further embodiment, each stator region 22 of the stator 20 including the permanent magnets 27A, 27B includes a stack in the rotational direction 4. The stack includes permanent magnets 27A, 27B having alternating magnetization directions parallel to the rotational direction 4, separated by blocks of the stator portion of the high permeability material 23, i.e., here electrical steel sheets 25. Thus, the stator periodicity, i.e., the average distance 21, is equal to the distance between every other permanent magnet.

[0066] In FIG. 1E, a part of one of the rotor region surfaces 14 is illustrated as seen from the air gap. The rotor region 12 of the rotor 10 includes a stack of blocks of electrical steel sheets 15 or other high permeability materials, arranged alternately with the distance blocks 17. The stack of electrical steel sheets 15 conducts the magnetic field well and thus presents high permeability in the cross-section 14. However, the distance blocks 17 are either provided slightly away from the air gap as in this embodiment or made of a non-magnetic material. Therefore, the distance blocks 17 present low permeability at the rotor region surface 14 facing the air gap. Thus, at each air gap in the rotational direction 4, the rotor 10 presents a variable permeability.

[0067] In this embodiment, each rotor section 12 of rotor 10 comprises a stack containing rotor sections of high-permeability material 13, in this case blocks of electrical steel sheets 15. The rotor sections of high-permeability material 13 have a major extension perpendicular to the direction of rotation 4. The rotor sections of high-permeability material 13 are separated by non-magnetic material or slits, i.e., distance blocks 17, or by the absence of material. Thus, the rotor periodicity is equal to the distance between two consecutive rotor sections of high-permeability material 13.

[0068] The average distance 11 between successive maxima of the variable permeability of the rotor 10 is illustrated by a double-headed arrow. In this particular embodiment, all distances between successive maxima of the variable permeability of the rotor 10 are the same, and therefore so is their average. However, in alternative embodiments, the rotor portions of high permeability material 13 may be provided somewhat displaced, which means that the distances between the maxima of the variable permeability of the rotor 10 may be somewhat different, but there will always be an average.

[0069] In Figure 1F, the same portion of rotor section 12 as in Figure 1E is illustrated in an orientation parallel to the air gap and perpendicular to the direction of rotation 4. Here, rotor section surfaces 14 and 16 are easily visible. The shown path 42 illustrates one example of how magnetic field lines pass between rotor section surfaces 14, 16 through magnetic material, including the rotor portion of high permeability material 13. Rotor section surfaces 14 and 16, in other words, are magnetically connected to one another.

[0070] The relationship between the rotor and the stator is also important. FIG. 1G illustrates several rotor and stator sections 12, 22 of the rotor 10 and the stator 20, schematically, along a portion of a path perpendicular to the direction of rotation 4. Here, the alternation of the rotor section 12 of the rotor 10 and the stator section 22 of the stator 20 is easily seen. Air gaps 40 separate the rotor and stator sections 12, 22 from each other. Here, it can also be seen that the magnetic portion of the rotor section 12 of the rotor 10 can conduct a magnetic field from the magnetic poles of the stator section 22 of the stator 20. Magnetic flux can thus be conducted primarily along the dotted arrows 44. Note that the illustrated magnetic flux passes through each air gap 40 in the same direction, i.e., to the left in the figure.

[0071] FIG. 1H illustrates schematically the rotor and stator sections 12, 22 of the rotor 10 and stator 20 of FIG. 1G when the rotor 10 and stator 20 are displaced relative to each other in the direction of rotation 4 by a distance equal to half the average distance 11. The magnetic flux situation now changes completely. The path of the magnetic flux is now to the right of the figure, as illustrated by the dotted arrow 45. In each air gap 40, the magnetic flux now changes direction.

[0072] Note in Figures 1G and 1H that the effect of having the magnetic flux in the same direction across all air gaps at each instant is achieved by matching the distance 11 in the rotor 10 to the distance 21 in the stator 20. To achieve the maximum change in magnetic flux, these average distances must be the same. However, it is possible to deviate from this requirement and still have an operational machine, at the expense of some shear stress and efficiency. For example, a slight deviation in the average distance can be provided to reduce force fluctuations and the so-called cogging effect, to reduce vibration, and to facilitate motor starting. So-called skewing can also be used, in which the magnetic materials in either the rotor 10 or the stator 20 are skewed so that they are oblique to each other in the direction of rotation 4.

[0073] 2A-D, several embodiments of rotor 10 and stator 20 having different periodicities in the direction of rotation 4 are schematically illustrated. In FIG. 2A, the periodicity of rotor 10, represented by average distance 11, is slightly different from the periodicity of stator 20, represented by average distance 21. However, this difference is still small enough to achieve overall constructive motion. In FIG. 2B, the average periodicity is the same for both rotor and stator, but rotor 10 has different individual distances 11' and 11" between successive structural repeats. In FIG. 2C, it is stator 20 that instead has different individual distances 21' and 21". In FIG. 2D, both rotor and stator 10, 20 have different individual distances between their respective structural repeats, and also have small differences in average distances 11, 21. Other configurations are, of course, possible.

[0074] Due to the curvature, the magnetic structures at the outside may have different average distances 11, 21 to the curvature, as discussed further below. However, for each section of the rotor, there will always be a neighboring section of the stator that presents an average distance that falls within the limits discussed herein above.

[0075] It is considered herein that such deviation in the mean distance should not exceed 35%. In other words, the rotor mean distance, determined as the mean distance between successive maxima of the variable magnetic permeability of the rotor section 12 of the rotor 10, is equal to or within 35% of the stator mean distance, determined as the mean distance between successive magnetic poles of the same polarity of neighboring stator sections. Preferably, the mean distances should be kept as close to each other as possible. Thus, in a preferred embodiment, the deviation in the mean distances of the rotor and stator should not exceed 30%, more preferably not exceed 20%, and most preferably not exceed 10%.

[0076] When specifying the maximum value of the variable permeability, it is the overall variation of the repeating structures that is intended to be taken into account. Minor variations that may produce small local maxima without affecting the overall energy transformation in the outer air gap shall not be considered as maxima in this respect. Similarly, other minor structures that produce small extensional permeability variations and do not contribute to the energy transformation in the outer air gap shall be ignored. Local maxima having a width less than 20% of the width of the widest main maximum are considered to be of little importance to the operation of the machine and should be ignored when specifying the average distance between maxima.

[0077] Similarly, if the periodicity is interrupted by missing major maxima, causing the distance between successive major maxima to double, the performance characteristics will be somewhat degraded but will still be useful in most cases. Such omitted maxima should also be ignored when defining the average distance between maxima in an otherwise repetitive structure.

[0078] The technology disclosed herein is therefore based on the fundamental principle of magnetic flux across an air gap varying in magnitude and direction depending on the relative position between two magnetic structures, a rotor and a stator. Ideally, all magnetic flux across the air gap, ignoring undesirable leakage flux, would be directed in the same direction at the direct position. The machine is therefore a flux-switching machine. In this disclosure, a flux-switching machine is defined as an electric machine that operates by switching magnetic flux and thus implements so-called magnetic gearing.

[0079] In an ideal world, all of the magnetic flux would pass through the air gap 40 into the opposite disk when the rotor portion of high permeability material 13 of the rotor 10 is aligned with the stator portion of high permeability material 23 of the stator 20. However, in the real world, there is always leakage flux. Thus, some flux will always leak back through the air gap 40 in the opposite direction. However, with careful design, the majority of the magnetic flux will be directed in the same direction, at least when the magnetic structures are aligned. The efficiency, shear stress, and power factor of the techniques presented here will generally increase if this majority is increased.

[0080] FIG. 3 illustrates these principles diagrammatically. The stator 20 presents alternating magnetic poles along the surface 24 facing the air gap 40. The magnetic flux passing from the north pole to the south pole is illustrated by arrows 43. Some, preferably most, of the magnetic flux passes through the rotor section to the next stator section, or, if the rotor section is the outer rotor section, turns back and passes through another part of the stator section. This is the magnetic flux utilized in the techniques presented here to achieve machine operation, i.e., the useful magnetic flux. Note that the air gap 40 in this illustration is dramatically exaggerated to increase the readability of the diagram. However, some magnetic flux leaks back into the same stator section without passing through any rotor section. When the situation at or near the surface 24 is considered, the magnetic flux passes outward, i.e., to the right in the diagram, as indicated by dashed line 49. In this situation, five arrows 43 cross line 49 and exit each north pole of the stator section. At the same time, the magnetic flux also passes inward, i.e., to the right in the diagram. In this situation, two arrows 43 cross the line 49 to reach each south pole of the stator section.

[0081] As briefly mentioned above, normal forces on magnetic materials in the air gap can be locally eliminated, except in the end cap areas. Forces from the rotor area on the stator area from one side are ideally canceled by equal forces from the rotor area on the opposite side. Similarly, forces from the stator area on one side on the inner rotor area are canceled by equal forces from the stator area on the opposite side. Thus, the forces are balanced, which significantly reduces the need for heavy and bulky structural materials. In the real world, deviations from perfect geometry always exist, and these deviations, according to Earnshaw's theorem, create non-cancelling normal forces. However, these forces are of a much smaller magnitude and are typically handled by the bearing systems that position the stator and rotor areas. The normal force elimination presented here, in a localized sense, has not previously been used in this manner for this type of machine.

[0082] The magnetic flux across the air gap therefore varies with changing the relative displacement of the rotor 10 and stator 20 along the direction of rotation 4. This is illustrated diagrammatically in Figure 4. By arranging the windings 30 to surround this variable magnetic flux, operation of the electric machine can be achieved.

[0083] FIG. 5 illustrates an embodiment of a winding 30 having loops 32, i.e., several turns, provided around an enclosed magnetic structure 70 in the stator section 22 of the stator 20 such that the winding creates one or more turns around the enclosed magnetic structure 70. The varying magnetic flux of FIG. 4 exists on the enclosed magnetic structure 70 in the stator section 22 of the stator 20. The loops 32 generally extend parallel to the direction of rotation 4. In other words, the loops 32 have their primary extension in the direction of rotation 4. To benefit from a substantially uniformly oriented magnetic flux to reduce winding resistance in relation to the amount of power converted, it is beneficial to have the loops encompass multiple pole-distances, i.e., the distance between consecutive magnetic poles of the same polarity, along the direction of rotation 4. To achieve significant benefits, it is believed herein that at least 2.5 pole-distances, corresponding to five magnetic poles, should be encompassed by at least one single loop 32. However, the more poles that are enclosed by a single loop, the less winding material is required in total, and the lower the resistive losses can be relative to the power converted. In Figure 5, nine poles are enclosed.

[0084] In one embodiment, the windings are wound non-perpendicular to the direction of rotation around an enclosed magnetic structure 70 within one or more stator sections 22 of the stator.

[0085] In a further embodiment, the loops of winding are wound parallel to the direction of rotation around a plurality of successive ones of the stator portions of magnetically permeable material.

[0086] The concept of magnetic gearing is used, whereby windings are wound around many poles rather than between each individual pole. This avoids the problem of windings becoming longer and thinner as poles are shortened, which limits the low-speed performance of standard machines. Typically, the entire phase is enclosed within a single loop, which means that the windings can be kept very short. Typically, the loop has a rectangular or similar shape. Also, the windings can be made several times thicker because there is more space available and short windings are less expensive. All together, this makes the winding resistance many times smaller than in standard machines.

[0087] Furthermore, to prevent magnetic flux from leaking outside the structure, it is beneficial to provide winding loops from the same phase surrounding the magnetic structures in several stator sections, the stator sections being arranged so that they are magnetically connected in series. This is discussed in more detail below. It is believed that an effect can be achieved by having winding loops from the same phase surrounding the magnetic structures in at least two of the stator sections. The more such stator sections are provided, the more power per unit weight that can be utilized and the lower the leakage magnetic flux. Preferably, at least three such stator sections are provided, more preferably at least four such stator sections are provided, and most preferably at least six such stator sections are provided. In the embodiment of FIG. 1A, there are winding loops from the same phase surrounding the magnetic structures in all three stator sections.

[0088] When the electric machine is operated as a generator, the rotor 10 and stator 20 are forced to move relative to one another, inducing a voltage in the loops 32 of the windings 30. Similarly, when the electric machine is operated as a motor, the changing current through the loops 32 of the windings 30 results in a force between the rotor 10 and stator 20, creating relative motion.

[0089] Thus, in one embodiment, the electric machine is a generator. Motion of the rotor relative to the stator causes an induced AC voltage to be produced in the windings.

[0090] In another embodiment, the electric machine is a motor. Alternating current conducted through windings causes relative motion between the rotor and the stator.

[0091] The geometry presented here magnetically connects many air gaps in series. This creates an array of sections with many air gaps between them. Because the magnetic flux density is divergence-free, the magnetic flux cannot vanish but must continue in a more or less closed loop. Therefore, if the array of sections itself does not form a loop (they would not if the sections were flat, for example), other blocks of magnetic material must be added to provide this function. These blocks of magnetic material are placed in the end caps or outer sections of the machine. Because the magnetic flux is large, the magnetic field lines within these blocks of magnetic material are long. It is preferable to avoid unnecessarily long magnetic field lines within blocks of magnetic material, such as iron, between air gaps, because these blocks do not provide force or power but only additional mass, additional losses, and additional cost. The size of the end caps is independent of the number of stator sections provided when the stator sections are magnetically connected in series. Therefore, the ratio of the end cap mass compared to the total mass of the machine is smaller when many stator sections are magnetically connected in series. This is also true for axial flux machines, but the scaling of the present invention is much more beneficial in this regard, since the stator sections can be made much thinner in the magnetic topology presented, so there is more to gain from magnetically connecting many stator sections in series in the present invention compared to axial flux machines.

[0092] In FIG. 1A, the winding topology can be seen, where each phase includes three phase winding loops magnetically connected in series. In this particular embodiment, the magnetic flux is returned through the other phases, forming a closed loop. Each phase thus resembles a sparse solenoid coil with an interior containing a mixture of materials. Leakage flux in such a coil is very low because the winding loops and the main reluctance in the magnetic circuit are in the same plane. The end caps, if properly dimensioned, form more or less magnetic short circuits, so that nearly all the reluctance in the magnetic circuit is located inside the winding loops. The main leakage flux present is that traveling between the windings and the enclosed magnetic structure and through the winding itself. This leakage flux is primarily axial in many geometries and is typically small compared to the flux passing through the enclosed magnetic structure. As a result, such machines can have an exceptionally high power factor compared to other modulated pole machines, reaching 0.8 in preferred embodiments. Such a geometric relationship also reduces problems with eddy currents in the windings and machine structure, as well as planar eddy currents in the electrical steel sheets.

[0093] The present technology therefore exploits geometric effects to increase the force or torque density of a machine and increase its efficiency. This is particularly evident at low speeds. In preferred embodiments, this can be achieved without even sacrificing power factor. The technology presented herein therefore has unprecedented performance in low-speed applications, such as direct drives, and in applications where high force or torque density is required. However, the present technology is not limited thereto. Suitable applications are generally renewable energy conversion systems, e.g., wind or ocean wave power generation, electric ship propulsion, gear motor replacements, direct drive applications, electric vehicles, and high force density actuators. However, the present technology is not limited thereto and can be used in many other applications as well.

[0094] In the above embodiment, stacks of permanent magnets 27A, 27B interleaved with stator sections of high-permeability material 23 are illustrated, acting as flux-concentrating structures. In other words, each stator section includes permanent magnets 27A, 27B arranged to present alternating poles along the surfaces 24, 26 facing the air gap 40, whereby the stator periodicity is equal to the distance between two consecutive poles of the same polarity. Preferably, the winding loops are wound parallel to the direction of rotation, surrounding multiple consecutive stator plates of magnetic material. However, the provision of a magnetic field can also be achieved by other configurations.

[0095] FIG. 6 schematically illustrates a side view of a modulated pole machine with surface-mounted magnets. This presents an alternative method of providing permanent magnet poles on the stator 20 along the air gap 40 in the direction of rotation 4. The stator 20 here includes a stator section 22 having a central body 29 of magnetic material. Surface-mounted permanent magnets 27C are provided on the surface of the central body 29. In such a design, the polarity of each side of the stator section 22 can be different, which means that the rotor section 12 of the rotor 10 can be mounted without displacement in the direction of rotation 4. However, because there is a magnetic force on the surface-mounted permanent magnets 27C perpendicular to the direction of rotation 4, there must be a means to ensure secure mounting of the surface-mounted permanent magnets 27C.

[0096] Most modulated pole machines include permanent magnets. However, in other embodiments, a switched reluctance machine design may be employed. FIG. 7 illustrates a side view of the relationship between the rotor 10 and stator 20 in such an approach. The stator 20 here includes a stator portion of high-permeability material 23, e.g., blocks of electrical steel sheets 25, arranged with essentially the same periodicity as the rotor portion of high-permeability material 13 of the rotor 10. Also, deviations from exact alignment of the periodicities may apply, as discussed further above. The stator 20 thus exhibits variable permeability in a direction parallel to the predetermined path of motion in each air gap. Note that the rotor periodicity here counts as two poles, i.e., one electrical period.

[0097] In other words, in one embodiment, both the stator 20 and the rotor 10 exhibit variable magnetic permeability in each air gap in a direction parallel to the predetermined path of motion, with the ratio of the respective periodicities being equal to an integer greater than one.

[0098] The force in switched reluctance embodiments is generated by a simple attractive force between the magnetic material in the rotor 10 and the magnetic material in the stator 20 when they are misaligned and magnetized by the current in the windings. This force can be in either direction depending on the relative positions of the rotor 10 and stator 20. Thus, one phase in a switched reluctance embodiment can only generate force in the desired direction for half, or two-quarters, of the electrical period and remains passive for the other two-quarters. This directly halves the average force density and is a drawback of machine types that double the number of phases required. Also, the force is generally less than in permanent magnet embodiments, which is a further disadvantage, and power factor and efficiency are lower. However, an advantage of switched reluctance embodiments is the absence of expensive permanent magnets in these embodiments, which lowers material costs and creates no dependency on the availability of permanent magnet materials such as neodymium and dysprosium for the manufacture of such units. Furthermore, when there is no current in the windings, there is no attractive force between the rotor 10 and the stator 20. Thus, manufacturing and assembly is significantly less complicated.

[0099] Thus, in one embodiment, at least one of the rotor sections preferably has a main extension perpendicular to the direction of rotation and comprises a stack of stator portions of magnetically permeable material separated by non-magnetic material or slits, whereby the stator mean distance is determined as the mean distance between successive stator portions of magnetically permeable material.

[0100] In a further embodiment, the loops of winding are wound parallel to the direction of rotation around a plurality of successive ones of the stator portions of magnetically permeable material.

[0101] It should be noted that in some embodiments, the switched reluctance approach may be combined with magnetized magnetic structures. To this end, some portions of the stator may be of the switched reluctance type as described hereinabove, while other sub-areas of the stator may have magnet-based structures, for example according to any of the embodiments described in connection with FIGS. 1A-6.

[0102] FIG. 8 illustrates one embodiment of a rotating machine in which two separate layers of coils exist radially within the stator section. The inner coils and their corresponding magnetic structures are 180 electrical degrees out of phase with the outer coils and their respective magnetic structures at the same mechanical angular position. A rotor 10 having a main toroidal shape presents a rotor section 12 with several rotor portions of high-permeability material 13 provided in the direction of rotation 4. The rotating electric machine 1 has six phases 2A-F in this embodiment, and depending on the detailed displacement of the rotors 10 of the different phases, the machine may be a one-, two-, three-, or six-phase machine. Such a machine may, of course, have any number of phases greater than one. Several loops 32 of windings are visible on the outside and inside of the main toroidal shape. The remainder of the stator is difficult to see in this view.

[0103] As briefly mentioned above, the rotor and stator sections 12, 22 on the inside of the curve, i.e., towards the center of the rotating machine, have a slightly smaller average distance between repeats of the magnetic behavior of the rotor and stator 10, 20 along the direction of rotation than the outer sections. However, typically, neighboring sections still fall within the 20% misalignment range discussed above.

[0104] FIG. 9 is a cutaway portion of the embodiment of FIG. 8. Here, it can be seen that a "racetrack-shaped" cross section is present. The long sides include alternating rotor and stator sections 12A, 22 of rotor 10 and stator 20, respectively. At both ends of the "racetrack," the outer rotor section 12D of rotor 10, which provides radial flux transport, closes the magnetic path into a closed circuit. Winding loops 32 are provided on the outside and inside of the "racetrack," i.e., the inside and outside of the closed magnetic section, separated by supporting distance blocks. The loops 32 are extended to encompass the portions of the stator 20 that belong to the machine's phases.

[0105] 8-9, it can be noted that the magnetic flux across the air gap 40 is primarily oriented in a poloidal direction. Because the machine operates due to the variation of the magnetic flux along the poloidal direction, this type of machine can therefore be referred to as a poloidal flux machine.

[0106] Thus, in one embodiment, the electric machine is a poloidal flux machine.

[0107] In rotary machines with only one phase in each stator section, the windings may be provided in a somewhat special manner. This is illustrated in FIG. 10. In this embodiment, the winding 30 is provided as one single loop that encircles the entire rotary machine, inside the magnetic path. Within one stator section, the loop may be divided into several winding turns, which are then adjacent loops.

[0108] This embodiment has the advantage of shorter windings associated with the enclosed magnetic flux compared to embodiments including several phase windings within each stator section, such as the embodiment shown in FIG. 1A, because no return winding is required, which reduces conduction losses for certain embodiments. This, in turn, reduces conduction losses for certain embodiments. A disadvantage is that a closed magnetic loop is required for each phase, including at least two stator sections and two end caps, and at least two, or preferably three, phases with separate magnetic circuits are required to generate the constant torque that is usually required. Therefore, each conductor ring magnetizes less material and generates less force, since the stator section air gap area must be smaller for the same total torque of the machine, which obscures the reduction in resistive losses. Also, because there are several stator sections per phase, more bearings are required, and the power factor is lower due to the presence of leakage flux inside the winding rings outside the air gap. Finally, more end caps are required.

[0109] In this disclosure, we often discuss winding loops. For clarity, when we discuss the length of this loop, it should be noted that this refers to the length of the conductor that forms the loop. Furthermore, if several turns of the same loop are made, the length should be taken for only one turn.

[0110] FIG. 11 shows an embodiment similar to that shown in FIG. 1A. This embodiment has six separate surrounded magnet structures on each stator section, each surrounded by a winding loop 32. However, these six surrounded magnet structures are organized into three pairs of adjacent surrounded magnet structures that are 180 electrical degrees out of phase with each other. Thus, the same phase winding is used to wind around both of these surrounded magnet structures, but in opposite directions. For example, the windings for 2A and 2A' are from the same phase. This embodiment thus forms a three-phase machine with phase windings 2A+2A', 2B+2B', and 2C+2C'. Each phase is now magnetically isolated from the others because the magnetic flux passing through the unprimed winding loops has a return path through the primed winding loops. This is beneficial from a controller perspective.

[0111] In all of the embodiments presented herein, there is one type of magnetic topology in the rotor and another type in the stator within an enclosed magnetic structure surrounded by the phase winding loops. However, in all of these embodiments, it is entirely possible to swap these magnetic topologies so that the magnetic topology in the rotor is instead placed in the stator within an enclosed magnetic structure surrounded by the windings, and the magnetic topology of the enclosed magnetic structure in the stator is instead implemented in the rotor. FIG. 12 illustrates such an embodiment. The new embodiment achieved by such a change results in a modulated pole machine with performance very similar to the original embodiment. A disadvantage of a permanent magnet machine in such an embodiment is that more magnets are needed if permanent magnets are placed in the rotor, since not all of the rotor surface area is used at the same time. On the other hand, an advantage is that since the stator does not contain permanent magnets, it is less expensive to increase the axial thickness of such a stator to better accommodate the winding material.

[0112] Similarly, the embodiments presented herein have end caps, outer rotor section 12B, belonging to the rotor. Alternatively, all embodiments herein may have end caps belonging to the stator, including the windings, instead, as illustrated in FIG. 12. The novel embodiment achieved by such a modification results in an electric machine operating by switching magnetic flux with performance very similar to the original embodiment.

[0113] 13A shows an embodiment in which the magnetic flux is primarily radial, rather than primarily axial as in the previous embodiment. In this particular embodiment, there are four stator sections 22 and five rotor sections 12, and the magnetic flux loops are closed in the outer rotor sections in the direction of rotation.

[0114] FIG. 13B shows a similar embodiment with magnetic flux that is primarily radial, but instead there are two parallel rows of magnetically active material in each section separated by an axial distance, and the magnetic flux loops are instead axially closed in the outer rotor section, forming poloidal flux loops.

[0115] Radial flux embodiments are more complex to build than their axial flux counterparts due to the more complex geometry, however the advantage is that the sections are stiffer due to the curvature, which facilitates building machines without local bearing arrangements.

[0116] In this technology, electrical steel is a popular choice for use as a highly permeable material in both the rotor and the stator. However, it is entirely possible to use a special type of electrical steel, grain-oriented electrical steel, in this concept. Grain-oriented electrical steel produces significantly lower iron losses than ordinary non-oriented electrical steel when the magnetic field is oriented in the preferred rolling direction and alternates back and forth in this direction instead of rotating. Therefore, it is typically used in transformers. In this invention, the magnetic field has this property, which greatly enables the use of grain-oriented electrical steel instead of non-oriented electrical steel to reduce iron losses during operation. Therefore, in one embodiment, the electric machine includes grain-oriented electrical steel.

[0117] The technology presented here has very good performance in low-speed applications, so the use of machines according to the previous description in low-speed applications is advantageous. The most important applications are probably direct-drive generators and motors, but systems operating at characteristic speeds below 5 m / s are also considered particularly suitable. The characteristic speed is defined as the typical relative speed of the rotor and stator in the air gap. Suitable applications are typically renewable energy conversion systems, wind power, tidal power, ocean wave power, electric ship propulsion, gear motor replacements, i.e., in gearless motors, traction motors, general direct-drive systems, and high-force-density actuators.

[0118] The above-described embodiments are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations, and changes can be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in different embodiments can be combined in other configurations, if technically possible. However, the scope of the present invention is defined by the appended claims.

[0119] References [1] EP3325800A1. [2] Hagnestal, Anders, and Erling Guldbrandzen. “A highly efficient and low-cost linear TFM generator for wave power.” EWTEC 2017: the 12th European Wave and Tidal Energy Conference 27th aug-1st Sept 2017, Cork, Ireland. European Wave and Tidal Energy Conference, 2017. [3] Hagnestal, A., 2016, “A low cost and highly efficient TFM generator for wave power,” The 3rd Asian Wave and Tidal Energy Conference AWTEC, pp. 822-828. [4] Hagnestal, A., 2018, “On the Optimal Pole Width for Direct Drive Linear Wave Power Generators Using Ferrite Magnets,” Energies, 11(6). [5] EP2982028A2. [6] Washington, Jamie G., et al. “Three-phase modulated pole machine topologies utilizing mutual flux paths.” IEEE Transactions on Energy Conversion 27.2 (2012): 507-515.

Claims

1. A rotating electrical machine (1) that is a modulated pole machine that operates by switching magnetic flux, A rotor (10), A stator (20); a winding (30); The winding (30) includes at least two phase windings (31); the rotor and stator (10, 20) include respective sections (12, 22) interleaved with one another via five or more air gaps (40), the air gaps (40) being parallel to a direction of rotation (4), the direction of rotation (4) being the direction of movement of the rotor (10) relative to the stator (20) in the air gaps (40); at least two different ones of the sections (12, 22), preferably at least three different ones of the sections (12, 22), and most preferably at least four different ones of the sections (12, 22) each include winding loops (32) from the same phase winding (31); At least one of the sections (12) that is part of the rotor (10) is an isolated rotor section that includes a non-conductive structural material; 1. A rotating electric machine (1) comprising: a winding loop (32) enclosing magnetic flux from at least five adjacent magnetic poles (N, S) in an air gap (40), the winding loop (32) enclosing a total magnetic flux greater than the magnetic flux from one individual magnetic pole (N, S), the adjacent magnetic poles (N, S) being provided on at least one of the rotor (10) and the stator (20).

2. A rotating electric machine as described in claim 1, characterized in that the winding loop (32) encloses a total magnetic flux greater than the magnetic flux from two individual magnetic poles (N, S) of the same polarity.

3. 3. A rotating electric machine according to claim 1, characterized in that the winding loop (32) encloses n magnetic poles (N, S) of the same polarity, n being greater than 2, preferably greater than 4, and more preferably greater than 6, the winding loop encloses a total magnetic flux greater than the magnetic flux from one individual pole, preferably greater than the magnetic flux from twice the magnetic flux from one individual pole, the winding loop length being less than 2*n*d, preferably less than n*d, where d is an air gap width distance which is the average width of the magnetically active part of the air gap (40) taken in a direction parallel to the air gap and perpendicular to the direction of rotation (4), and the magnetic poles are provided on at least one of the rotor (10) and the stator (20).

4. 4. A rotating electric machine according to claim 1, wherein at least one of the winding loops, being a first winding loop, encloses magnetic flux from at least five magnetic poles, and wherein at least 30%, preferably at least 50%, more preferably at least 70%, even more preferably at least 90%, and most preferably 100% of the magnetic flux from the at least five magnetic poles is outside all other winding loops belonging to another phase and located in the same area (12, 22) as the first winding loop.

5. A rotating electrical machine (1) according to any one of claims 1 to 4, characterized in that the sections (12, 22) are flat discs and the magnetic flux within the rotating electrical machine (1) is directed mainly axially.

6. A rotating electrical machine (1) according to any one of claims 1 to 4, characterized in that the rotating electrical machine (1) has a magnetic flux that is mainly oriented radially.

7. A rotating electrical machine according to any one of claims 1 to 6, characterized in that the rotating electrical machine (1) is a variable reluctance permanent magnet machine operating by switching magnetic flux.

8. A rotating electrical machine according to any one of claims 1 to 7, characterized in that the rotating electrical machine (1) comprises a ferrite magnet.

9. A rotating electrical machine according to any one of claims 1 to 8, characterized in that the rotating electrical machine (1) comprises neodymium magnets.

10. A rotating electrical machine (1) according to any one of claims 1 to 9, characterized in that the rotating electrical machine (1) comprises permanent magnets arranged in a flux-concentrating configuration.

11. 7. A rotating electric machine according to any one of claims 1 to 6, characterized in that the rotating electric machine is a switched reluctance machine in which both the stator (20) and the rotor (10) exhibit variable magnetic permeability in a direction parallel to a predetermined path of motion in each air gap.

12. A rotating electrical machine according to any one of claims 1 to 11, characterized in that the rotating electrical machine (1) comprises grain oriented electrical steel.

13. A rotary electric machine according to any one of claims 1 to 12, characterized in that at least one section (12, 22) comprises winding loops that are part of three or more different phases, preferably four or more different phases, more preferably five or more different phases, even more preferably six or more different phases, even more preferably seven or more different phases, even more preferably ten or more different phases, and most preferably thirteen or more different phases.

14. A rotating electrical machine according to any one of the preceding claims, characterized in that at least one section contains winding loops belonging to one phase but not to another phase.

15. A rotating electric machine according to any one of claims 1 to 14, characterized in that the rotating electric machine (1) has four or more phases, preferably seven or more phases, more preferably ten or more phases, even more preferably thirteen or more phases, and most preferably sixteen or more phases.

16. A system including a rotating electric machine (1) according to any one of claims 1 to 15, said system comprising: renewable energy conversion systems, wind power plants, tidal power plants, Ocean wave power plants, Electric ship propulsion systems, Gearless motor, Electric vehicles, Direct drive systems, and The system is selected from actuators with high force density.

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