Axial synchronous brushless motor, cryogenic plant comprising such a motor, and associated method for operating such a plant

Abstract

To provide a brushless electric motor which is very advanced in energy efficiency and environment-friendly.SOLUTION: The axial flow brushless motor 1 comprises at least one rotor formed by a first rotor disc, a first plurality of permanent magnets mechanically fixed to the first rotor disc, and a stator defined by a stator crown comprising a plurality of ferromagnetic cores, a plurality of winding sections and a plurality of support structures defining housing seats for the ferromagnetic cores. The winding sections are wound around the support structure, and each winding section defines a plurality of coils made of superconducting material. The motor comprises a cryostat 11 configured to define a circulation duct for a cryogenic fluid, the cryostat extending around the periphery of the stator and being configured to be in contact with each coil. An inlet opening 12 and an outlet opening 13 respectively allow the cryogenic fluid of the circulation duct to be introduced and extracted.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of electric motors, in particular to axial flow synchronous brushless motors.

[0002] The present invention relates to an axial-flow synchronous brushless motor, a cryogenic plant comprising such a motor, and a method for operating a cryogenic plant. [Background technology]

[0003] The field of synchronous axial motors has been an interesting solution for the automotive, marine propulsion and electric vehicle industries for several years now.

[0004] In practice, it is known that electric machines of axial flow and permanent magnet configuration generally provide greater torque for a given motor displacement than synchronous radial flow machines, since the area of ​​active magnetic surface is at the rotor face of the motor rather than the outer diameter.

[0005] In practice, that is to say, the surfaces on which the conductors and permanent magnets are placed are therefore perpendicular to the axis of the machine.

[0006] In radial flow machines the relationship between torque and diameter is a power of two, while in axial flow machines the relationship is a power of three.

[0007] For this reason, axial motors are known to be much more compact and lightweight than radial motors of comparable power output, and to have greater power density and torque.

[0008] Furthermore, an axial flow electric motor has a different appearance compared to a radial flow motor; under the condition of equal torque generation, an axial flow motor has a larger diameter, a smaller width, and a smaller overall axial dimension.

[0009] It is known that in radial flow machines most of the windings are inactive, whereas in axial flow motors 100% of the windings are active, which offers considerable advantages in terms of weight / power ratio.

[0010] It is also known that if the copper windings and / or permanent magnets are made using superconducting materials, they allow for a high current density in the windings and a high density of magnetic flow induced in the air gap, keeping current losses to zero and eliminating problems due to de-fluxing, i.e., loss of magnetic flow.

[0011] In fact, superconductors have the properties of high current density, zero electrical resistance to the passage of direct current, and therefore no losses due to the Joule effect, which reduces the weight and cross-sectional area of ​​the windings and increases efficiency at all speeds. Summary of the Invention

[0012] In this context, the technical object underlying the present invention is to propose an axial flow synchronous brushless motor that overcomes the above-mentioned drawbacks.

[0013] In particular, it is an object of the present invention to provide a brushless electric motor that is highly advanced in terms of energy efficiency and environmental friendliness.

[0014] A further object of the present invention is to provide a motor that is extremely compact and lightweight.

[0015] A further object of the present invention is to provide a motor with high performance levels, and therefore greater power and torque density, compared to radial motors of comparable power.

[0016] The invention also relates to a cryogenic plant for cooling a cryogenic fluid entering a cryostat.

[0017] The present invention also relates to a method for operating a cryogenic plant.

[0018] The indicated technical and stated objects are substantially achieved by a synchronous brushless electric motor, a cryogenic plant, and a method for operating a cryogenic plant, which comprise the technical features set forth in one or more of the appended claims. [Brief explanation of the drawings]

[0019] Further features and advantages of the present invention will become more apparent from the following non-limiting description with reference to preferred but non-exclusive embodiments of a brushless electric motor as illustrated in the accompanying drawings. [Figure 1] 1 shows a perspective view of a motor according to the present invention; [Figure 2] 1 shows a first cross section of a motor according to the invention; [Figure 3] 3 shows a perspective view of the rotor disk with the respective permanent magnets of the motor according to the invention shown in FIGS. 1 and 2; FIG. [Figure 4] 1 shows a schematic diagram of a stator yoke of a motor according to the present invention; [Figure 5] 1 shows a schematic diagram of a stator crown wound with a superconducting coil (HTS coil) according to the present invention. [Figure 6] 1 shows a schematic diagram of a superconducting coil (HTS coil) of a motor according to the present invention. [Figure 7] 1 shows a schematic cross-sectional view of a motor according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0020] FIG. 1 shows a cross section of an axial synchronous brushless electric motor according to the invention, which for ease of explanation will be referred to in the following as motor 1.

[0021] In particular, as shown in FIGS. 1 to 5, the present invention provides a motor 1 comprising at least: a rotor defined by a first rotor disc (2); a first plurality of permanent magnets 3 mechanically fixed (i.e. fixed in use) to the first rotor disc 2; It concerns a motor 1 having a stator defined by a stator crown 4 with a plurality of ferromagnetic cores 5, a plurality of winding sections, and a plurality of respective support structures 6 defining accommodation seats for the ferromagnetic cores 5.

[0022] It should be noted that the winding sections are wound on a support structure 6 .

[0023] Each winding section defines a number of coils 7 made of superconducting material (HTS - High Temperature Superconducting coils).

[0024] According to one aspect of the present invention, the motor 1 also comprises a second rotor disc 8 and a second plurality of permanent magnets 9 fixed to the second rotor disc 8 (i.e. fixed in use).

[0025] Both the first rotor disk 2 and the second rotor disk 8 each rest on bearings fixed between the cryostat and the rotor disks (2, 8).

[0026] Permanent magnets 3 and 9 are magnets synthesized with rare earth elements, especially neodymium-iron-boron (N d F e B) It is made up of magnets.

[0027] N d F e Magnets made from B alloy are among the strongest permanent magnets on the rare earth sintered magnet market, with high resistance to demagnetization.

[0028] According to the embodiment shown in FIG. 3, the first plurality of permanent magnets 3 faces the second plurality of permanent magnets 9 .

[0029] The first plurality of permanent magnets 3 of the first rotor disk 2 and the second plurality of permanent magnets 9 of the second rotor disk 8 may be arranged relative to each other such that the north poles of the permanent magnets of the first rotor disk 2 face the south poles of the permanent magnets of the second rotor disk 8, and also such that the south poles of the permanent magnets of the first rotor disk 2 face the north poles of the permanent magnets of the second rotor disk 8.

[0030] According to this embodiment, by way of non-limiting example, twelve permanent magnets are arranged on the first rotor disk 2 and the second rotor disk 8 .

[0031] Furthermore, both the first rotor disc 2 and the second rotor disc 8 are fixed to the same axis "Z" and rotate at the same speed (Figure 3), and comprise the excitation winding (or "field" winding).

[0032] According to another embodiment, the stator crown 4 comprises a plurality of support structures 6, each of which defines a first seat 6a and a second seat 6b (as can be clearly seen in FIG. 4).

[0033] Each seat 6 a , 6 b is configured to partially house a ferromagnetic core 5 .

[0034] In other words, the support structure 6 is defined to partially house the ferromagnetic core 5 and constitutes a stator yoke through which the field lines of the magnetic field generated by the permanent magnets 3 and 9 pass axially (parallel to the axis "Z").

[0035] According to the embodiment shown in FIG. 5, the stator crown 4 is of a slotted and toothed construction so as to make the motor 1 anisotropic from a magnetic point of view.

[0036] According to this embodiment, the ferromagnetic cores 5 are considered to be teeth of the stator crown 4 .

[0037] According to one embodiment, the ferromagnetic core 5 is made of ferromagnetic plates so as to reduce losses due to the Joule effect due to the current induced therein.

[0038] According to another embodiment, the arrangement of the coils 7 is chosen according to the star of slots theory.

[0039] Each ferromagnetic core 5 is inserted inside the first and / or second sheet of the structure 6a and / or 6b.

[0040] Each ferromagnetic core 5 also has two ends 5a and 5b (clearly shown in Figure 5) that each face the first plurality of permanent magnets 3 of the first rotor disk 2 and / or the second plurality of permanent magnets 9 of the second rotor disk 8.

[0041] In other words, inside the first and / or second sheet of the structure 6a and / or 6b there is a core made of ferromagnetic material 5, which is also trapezoidal and carries at its ends 5a and 5b two plates made of ferromagnetic material 5.

[0042] The stator yoke also comprises a plate-like element 10 formed to a suitable shape and preferably made of steel.

[0043] The HTS tape of each reel 7 is wrapped around the plate-like metal element 10 after being electrically insulated, by way of non-limiting example, insulating paint or Kapton tape applied to the plate-like metal element 10 itself.

[0044] Referring to Figure 6, each coil 7 comprises a first portion 7a and a second portion 7b.

[0045] The first portion 7a is inserted into the first seat 6a of the support structure 6 in use, and the second portion 7b is inserted into the second seat 6b of the support structure 6 in use.

[0046] According to one embodiment, each reel 7 is configured to define a double pancake shape.

[0047] As shown in Figures 6 and 7, the first portion 7a of the reel 7 and the second portion 7b of the coil 7 are defined by a single HTS tape, and in particular, the first portion 7a of the coil 7 is defined by a portion of the HTS tape wound from the outside to the inside of the coil 7, and the second portion 7b of the coil 7 is defined by a portion of the HTS tape wound from the inside to the outside of the coil 7.

[0048] In other words, the HTS tape is used to wind each reel 7 in a double pancake shape.

[0049] The double pancake configuration consists of two pancake-shaped windings placed parallel, one above the other, with the HTS tape running continuously from one winding section to the other.

[0050] Each pancake consists of a single layer of N concentric turns separated from each other.

[0051] This shape is characterized in that the first portion 7a of the coil 7 is wound from the outside to the inside, and the second portion 7b of the coil 7 is wound from the inside to the outside.

[0052] In this way, both ends of the coil 7 are on the outside and therefore easily accessible.

[0053] The motor 1 also includes a cryostat 11 configured to define a duct for circulating a cryogenic fluid. The cryostat extends around the outer periphery of the stator 4 and is configured to contact each of the plurality of coils 7.

[0054] In other words, the superconducting coils 7 forming the windings of the motor must be surrounded by a suitable cryostat 11 .

[0055] Both the first rotor disk 2 and the second rotor disk 8 rest on bearings fixed to the cryostat 11 .

[0056] The cryostat 11 has an inlet opening 12 and an outlet opening 13 that allow the introduction and extraction, respectively, of the cryogenic fluid in the circulation duct.

[0057] It should also be noted that the cryostat 11 is configured to accommodate the coil 7 in the circulation duct.

[0058] In other words, the cryostat 11 may be shaped like a container, inside which a suitable cryogenic fluid, for example nitrogen, is introduced to the coil 7 at the operating temperature (T op ) to the critical temperature (T c ) to keep it below the water level.

[0059] Critical temperature value T c is specific to the material, i.e., the HTS tape used in each reel.

[0060] Critical temperature T c is the temperature at which the superconducting material forming the coil (7) loses its superconducting properties and reverts to insulating ceramic material.

[0061] In other words, the cryocooler (i.e., the cryogenic cooler) processes, i.e., removes, the heat associated with the losses of each coil 7, and maintains the operating temperature T op is provided to provide all the cooling power necessary to keep the

[0062] In fact, the HTS tape from which reel 7 is made is a source of electrical losses, called AC losses, when it operates in a magnetic field / alternating current (as in the case of the windings of a synchronous machine).

[0063] Operating temperature T op The increase in CO₂ reduces the energy costs of operating the plant.

[0064] In fact, under conditions of equal compressor mechanical power and therefore energy consumption, the cooling power of a cryocooler depends strongly on the temperature at which it is produced.

[0065] In order to limit the heat load associated with alternating current losses (i.e., AC losses) in the coils 7 and therefore dissipate only the heat associated with these losses, according to one aspect of the present invention, the ferromagnetic core 5 of each coil 7 is located outside the cryostat 11.

[0066] In doing so, despite being separated by only a few millimeters, the coil 7 and the ferromagnetic core 5 operate at different temperatures, namely 40 / 50K and 300K respectively.

[0067] According to another aspect, the cryostat 11 defines a vacuum chamber 40 (within which a vacuum is formed) such that the temperature difference between the internal and external environments is kept constant and heat exchange between the two environments (inside and outside the chamber) is minimized.

[0068] The cryostat 11 thus forms the support structure for the motor 1, the containment chamber for each ferromagnetic core 5, and the vacuum chamber 40 (as shown in FIG. 2).

[0069] To create a vacuum inside the vacuum chamber 40, the cryostat 11 has a conduit 20 connected to a valve which, in use, can be connected to a vacuum pump to extract air from the inside of the vacuum chamber 40, thus creating a vacuum.

[0070] According to one embodiment, the walls of the cryostat 11 are glazed (to reduce radiation).

[0071] According to another embodiment, the only place where there is no vacuum in the cryostat 11 of the motor 1 according to the invention is made with minimal dimensions.

[0072] According to the embodiment shown in FIG. 7, the core of ferromagnetic material 5 is designed to transmit the field lines of the magnetic field and maintain a high value of magnetic current density associated with the coil 7, so that it is possible to distinguish between the mechanical gap "M" and the electromagnetic gap "E", despite the presence of the cryostat 11.

[0073] The mechanical gap "M" is the space that exists between an end of the ferromagnetic core (eg, top end 5a) and one of the permanent magnets (eg, of the first plurality of permanent magnets 3).

[0074] Preferably, according to one embodiment, the mechanical air gap "M" is between 0.2 mm and 1 mm, more preferably between 0.5 mm and 0.85 mm.

[0075] The mechanical gap "M" is measured along axis "Z" between the plate of ferromagnetic material 5a and the edge of the permanent magnet 3.

[0076] On the other hand, the electromagnetic gap "E" is the space that exists between the edge of each coil 7 and the edge of each permanent magnet 3 of the first rotor disk 2 or the second rotor disk 8, i.e., the average circumference of the electromagnetic gap "E" is taken as the basis for estimating the electrical and magnetic quantities for sizing purposes.

[0077] Also, in the embodiment shown in FIG. 7, the mechanical gap "M" has a smaller value than the electromagnetic gap "E."

[0078] According to one aspect of the present invention, the cryostat 11 comprises at least one sensor configured to monitor the magnetic field generated by each coil 7, and / or the operating temperature of each coil 7, and / or the current passing through each coil 7.

[0079] The motor 1 also comprises a control unit (not shown) associated with at least one sensor, the control unit being configured, in use, to regulate the flow rate of the cryogenic fluid in the circulation duct depending on the magnetic field, and / or temperature, and / or current measured by the sensor.

[0080] Preferably, the motor 1 comprises at least one valve for adjusting the flow rate of the cryogenic fluid in the circulation duct depending on the magnetic field measured by the sensor, and / or the temperature, and / or the current.

[0081] According to this embodiment, the control unit is connected to the valve and adjusts the opening degree, thus adjusting the flow rate of the cryogenic fluid in the circulation duct.

[0082] The invention also provides a cryogenic plant comprising a motor 1 and a circuit for introducing a cryogenic fluid into a circulation duct.

[0083] In particular, a circuit for introducing cryogenic fluid is connected to an inlet opening 12 and an outlet opening 13 of a cryostat 11 of the motor 1. The motor 1 is arranged, in use, to deliver a portion of its power to operate a compressor which delivers power to the cryostat 11 so as to generate a flow of cryogenic fluid between the inlet opening 12 and the outlet opening 13 of the cryostat 11.

[0084] In other words, the motor 1 transmits the generated power to the compressor which supplies it to the cryostat 11 for moving the cryogenic fluid inside the circulation duct, and the coils 7, in use, to their operating temperature T without exceeding the critical temperature Tc. op It is configured to keep

[0085] In practice, the stator also has three inlet conduits 14, 15 and 16 fixed to it for the electrical cables, in particular one for each of the three stages.

[0086] For this reason, each coil 7 operating in AC mode is monitored to ensure that the magnetic field, temperature and current do not exceed critical values.

[0087] The invention also relates to a method for operating a cryogenic plant, comprising the steps of: supplying the cryogenic plant with a cryogenic fluid at a predetermined temperature; conveying the power generated by the motor 1 to a circulation duct so as to generate a flow of the cryogenic fluid between the inlet opening 12 and the outlet opening 13 of the cryostat 11; and finally cooling the coil 7 by the cryogenic fluid flowing in the circulation duct, in particular from the inlet opening 12 to the outlet opening 13 of the cryostat 11.

[0088] It should be noted that the motor 1 according to the invention can be applied in various industrial fields, for example in automotive, marine propulsion and electric vehicles.

[0089] Furthermore, the motor 1 may advantageously be applied to a compressor of a cryogenic plant in order to drive said compressor.

[0090] Advantageously, the motor 1 according to the invention makes it possible to overcome the above-mentioned drawbacks of the prior art.

[0091] Advantageously, a very energy efficient (approximately 99%) motor 1 is provided, which is very advanced and environmentally friendly in terms of energy efficiency.

[0092] In other words, the motor 1 according to the present invention complies with the energy efficiency regulation IE4.

[0093] Advantageously, the motor 1 is much more compact and lighter than prior art motors: in fact, currently, a conventional electric motor with an output of 500 kW weighs 330 kg, whereas the motor 1 according to the invention weighs 30 kg, has an outer diameter of about 250 mm and a thickness of about 100 mm.

[0094] In particular, the compactness and lightness of the motor 1 are achieved by optimizing the use of materials and components used to form its internal structure, a feature that also makes it possible to use the motor 1 in aircraft.

Claims

1. An axial flow brushless motor (1) comprising at least: a rotor formed by a first rotor disc (2), a first plurality of permanent magnets (3) mechanically fixed to said first rotor disc (2); a stator defined by a stator crown (4) comprising a plurality of ferromagnetic cores (5), a plurality of winding sections and a plurality of support structures (6) defining a containment seat for said ferromagnetic cores (5) and a support for said winding sections, each winding section defining a plurality of coils (7) made of superconducting material (HTS coils), The motor (1) further comprises a cryostat (11) configured to define a circulation duct for a cryogenic fluid, the cryostat (11) extending around the outer periphery of the stator and configured to contact each coil (7) of the plurality of coils (7), the cryostat (11) having an inlet opening (12) and an outlet opening (13) allowing the introduction and extraction of the cryogenic fluid from the circulation duct, respectively.

2. 2. The motor (1) according to claim 1, wherein the cryostat (11) comprises at least one sensor configured to monitor the magnetic field generated by each coil (7) and / or the operating temperature of each coil (7) and / or the current passing through each coil (7), and wherein the motor (1) also comprises a control unit associated with the at least one sensor, the control unit being configured, in use, to regulate the flow rate of the cryogenic fluid in the circulation duct depending on the magnetic field and / or the temperature and / or the current measured by the sensor.

3. 3. The motor (1) according to claim 2, wherein the control unit is configured to increase the flow rate of the cryogenic fluid in the circulation duct if the magnetic field and / or temperature and / or current exceed a preset threshold.

4. 4. The motor (1) according to any one of claims 1 to 3, wherein the rotor also comprises a second rotor disk (8) and a second plurality of permanent magnets (9) mechanically fixed to the second rotor disk (8).

5. 5. The motor (1) according to any one of claims 1 to 4 and claim 4, wherein the first plurality of permanent magnets (3) faces the second plurality of permanent magnets (9).

6. 6. The motor (1) according to claim 5, wherein the permanent magnets of the first rotor disk (2) and the permanent magnets of the second rotor disk (8) are arranged relative to each other such that the north poles of the permanent magnets of the first rotor disk (2) face the south poles of the permanent magnets of the second rotor disk (8).

7. 7. A motor (1) according to any one of claims 1 to 6, wherein each support structure (6) defines a first seat (6a) and a second seat (6b), each seat being configured to partially house a ferromagnetic core (5), and each coil (7) comprises a first portion (7a) and a second portion (7b), the first portion (7a) being inserted into the first seat (6a) in use, and the second portion (7b) being inserted into the second seat (6b) in use.

8. A motor (1) according to any one of claims 1 to 7 and claim 7, wherein the first portion (7a) of the reel (7) and the second portion (7b) of the coil (7) are defined by a single tape, in particular, the first portion (7a) of the coil (7) is defined by a portion of the tape wound from the outside to the inside of the coil (7), and the second portion (7b) of the coil (7) is defined by a portion of the tape wound from the inside to the outside of the coil (7).

9. 9. The motor (1) according to claim 1, wherein each ferromagnetic core (5) is inserted into the first seat (6a) and / or the second seat (6b), and each ferromagnetic core (5) also has two ends (5a and 5b) that face the permanent magnets (3 and / or 9) of the first rotor disk (2) and / or the second rotor disk (8).

10. 10. The motor (1) according to any one of claims 1 to 9, wherein each coil (7) is configured to define a double pancake shape.

11. Motor (1) according to any one of claims 1 to 10, wherein the permanent magnets (3 and 9) comprise rare earth sintered magnets, in particular neodymium-iron-boron magnets.

12. 12. The motor (1) according to any one of the preceding claims, wherein the cryostat (11) is configured to accommodate the coil (7) within the circulation duct.

13. 13. The motor (1) according to any one of claims 1 to 12, wherein the cryostat (11) defines a vacuum chamber (40) and has a conduit (20) and a valve.

14. 14. A cryogenic plant comprising a motor (1) according to any one of claims 1 to 13 and a circuit for introducing a cryogenic fluid, in particular liquid nitrogen, into the circulation duct connected to the inlet opening (12) and the outlet opening (13) of the cryostat (11) of the motor (1), wherein the motor (1) is configured, in use, to transmit a part of its power to supply the cryostat (11) and the inlet circuit so as to generate a flow of the cryogenic fluid between the inlet opening (12) and the outlet opening (13) of the cryostat (11).

15. 15. A method for operating a cryogenic plant according to claim 14, comprising: - supplying a cryogenic fluid at a predetermined temperature to the cryogenic system; - supplying the power of the motor (1) to the cryostat (11) so as to generate a flow of the cryogenic fluid between the inlet opening (11) and the outlet opening (12) of the cryostat (13); - cooling the coil (7) using the cryogenic fluid flowing in the circulation duct, in particular from the inlet opening (12) to the outlet opening (13) of the cryostat (11).

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