A low-loss superconducting motor and its design method

Abstract

This invention relates to the field of superconducting motor technology, and in particular to a low-loss superconducting motor and its design method. The low-loss superconducting motor includes a vacuum chamber, a stator assembly, and a mover assembly. The stator assembly includes a stator support frame with a planar top structure and a superconducting coil disposed on the planar structure. A protective cover is disposed above the superconducting coil, and a radiative heat shield is disposed on the protective cover. The mover assembly is disposed between the protective cover and the radiative heat shield. The mover assembly includes a frame-shaped mover support frame and a constant conductor coil. The temperature of the constant conductor coil is controlled by controlling the emissivity of the radiative heat shield, and the surface emissivity of the protective cover is used to cool the constant conductor coil. The invention also discloses a design method based on a low-loss superconducting motor. The air gap between the stator assembly and the mover assembly is small, which facilitates the achievement of a high magnetic field, reduces the Joule loss of the constant conductor coil, eliminates the need for air or water cooling pipes, and facilitates temperature control.

Description

[0001] This application is a divisional application of the following application: filed on October 14, 2024, application number 202411433110.7, entitled "A Low-Loss Superconducting Motor and Its Design Method". Technical Field

[0002] This invention relates to the field of superconducting motor technology, and in particular to a low-loss superconducting motor and its design method. Background Technology

[0003] Superconducting motors, whose windings are made of practical superconducting wire, possess advantages such as high power density and high efficiency, making them promising motors. Superconducting motors are structurally classified into fully superconducting motors and semi-superconducting motors. In fully superconducting motors, both the stator and rotor are superconductors, installed in a cryogenic bath (vacuum chamber). The small air gap between the stator and rotor facilitates the achievement of high magnetic fields. However, the superconducting coils subjected to alternating current suffer from high losses, making it difficult for the rotor to rotate at high speeds within the cryogenic bath, and cooling is challenging, requiring complex mechanical or electrical systems for safe operation. In semi-superconducting motors, one stator is a superconductor, and the other a constant conductor. One stator is installed inside the cryogenic bath, while the other is installed outside. The cryogenic bath wall separates the stator and rotor, resulting in a large air gap between them, making it difficult to achieve high magnetic fields. Joule losses due to alternating magnetic fields still exist. Summary of the Invention

[0004] The purpose of this invention is to provide a low-loss superconducting motor and its design method to solve the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides a low-loss superconducting motor, including a vacuum chamber, a stator assembly and a mover assembly disposed within the vacuum chamber. The stator assembly includes a stator support frame with a planar top structure, on which a plurality of arrayed superconducting coils are disposed. Adjacent superconducting coils have different vertical polarities. A protective cover is disposed above the arrayed superconducting coils, and a radiative heat shield is disposed on the protective cover. A mover assembly is disposed between the protective cover and the radiative heat shield. The mover assembly includes a frame-shaped mover support frame, within which at least one set of constant conductor coils is disposed. Each set of constant conductor coils includes at least two constant conductor coils. The temperature of the constant conductor coils is controlled by controlling the emissivity of the radiative heat shield, and the surface emissivity of the protective cover is used to cool the constant conductor coils.

[0006] Preferably, the planar structure is covered with multiple layers of heat-insulating film to suppress radiant heat from the vacuum chamber.

[0007] Preferably, the protective cover is made of non-metallic material.

[0008] Based on the above-mentioned design method for a low-loss superconducting motor, the specific steps are as follows:

[0009] The specific steps are as follows:

[0010] Step S1: Calculate the stator magnetic field based on the required acceleration;

[0011] Step S2: Calculate the current in the superconductor coil based on the stator magnetic field;

[0012] Step S3: Calculate the critical current and superconductor temperature based on the current in the superconductor coil;

[0013] Step S4: Determine the cooling system based on the superconductor temperature;

[0014] Step S4 is as follows:

[0015] Step S41: Calculate the heat transfer, which includes radiative heat transfer, conductive heat transfer, and wire heat transfer.

[0016] Step S42: Calculate the heat required for cooling based on the balance relationship of each heat transfer process;

[0017] The formula for calculating the heat required for cooling is as follows:

[0018] Q c =N sup ·(Q L +Q U )+Q W +Q AC

[0019] Among them, Q c To cool the heat required by the superconductor coil, N sup Q represents the number of superconducting coils. L Heat conduction on the lower surface of each superconducting coil, Q U Heat is conducted on the upper surface of each superconducting coil, Q W Q represents the heat transfer from the conductor to the superconducting coil. AC The superconducting coil loses heat through alternating current.

[0020] Step S43: Determine the refrigeration system based on the heat required for cooling. The heat required to cool the superconductor coil is less than the refrigeration capacity of the refrigeration mechanism.

[0021] Therefore, the present invention employs the above-mentioned low-loss superconducting motor and its design method, which has the following advantages: the air gap between the stator assembly and the mover assembly is small, it is easy to achieve a high magnetic field, reduce the Joule loss of the constant conductor coil, eliminate the need for air or water cooling pipes, and facilitate temperature control.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view of a low-loss superconducting motor according to the present invention;

[0024] Figure 2 This is a perspective view of a low-loss superconducting motor according to the present invention;

[0025] Figure 3 This is a diagram showing the distribution of the constant conductor coils in a low-loss superconducting motor according to the present invention.

[0026] Figure 4 This is a schematic diagram of a low-loss superconducting motor superconductor coil structure according to the present invention;

[0027] Figure 5 A graph showing the relationship between the stage acceleration and the stator magnetic field;

[0028] Figure 6 The graph shows the relationship between the current in the superconducting coil and the stator magnetic field.

[0029] Figure 7 A graph showing the relationship between the temperature and current of a superconducting coil.

[0030] Figure 8 Temperature range diagram for superconductor coil design;

[0031] Figure 9 A graph showing the relationship between stage acceleration and superconductor coil temperature;

[0032] Figure 10 This is a diagram of a thermal analysis model inside a vacuum chamber;

[0033] Figure 11 This is a diagram of an analytical model for a constant conductor coil.

[0034] Figure 12 A graph showing the relationship between the heat required for cooling and the temperature of the superconductor coil.

[0035] Figure Labels

[0036] 1. Vacuum chamber; 2. Mover support frame; 3. Stator support frame; 4. Normal conductor coil; 5. Superconductor coil; 6. Protective cover; 7. Radiant heat shield.

[0037] It should be noted that since this embodiment is for a planar motor, and embodiment 2 in the parent design also explicitly states that it is for a planar motor, it also implicitly discloses that the mover support frame moves linearly. Therefore, the modifications in the parent design regarding the rotor part to a mover, the rotor coil to a constant conductor coil, and the rotor magnetic field to a mover magnetic field are all corresponding modifications to the original technical solution of the parent design and do not exceed the scope of the modification. Detailed Implementation

[0038] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0040] Example 1

[0041] like Figures 1-2 As shown, a low-loss superconducting motor includes a vacuum chamber 1, in which a stator assembly and a mover assembly are disposed.

[0042] The stator assembly includes a stator support frame 3 with a planar top structure, on which several arrayed superconducting coils 5 are arranged, such as... Figure 4 As shown, adjacent superconducting coils 5 have different vertical polarities, and superconducting coil 5 has a height of H. s The cylindrical coils 5 have different vertical polarities between adjacent superconductor coils 5, i.e., N and S poles are arranged alternately. This embodiment has 36 N poles and 25 S poles. The planar structure is covered with multiple layers of heat insulation film to suppress radiative heat from the inner wall of the vacuum chamber 1, thereby maintaining a low surface emissivity. Furthermore, the stator support frame 3 is made of G10 material, which has the advantages of low thermal conductivity and relatively high rigidity. The material of the stator support frame 3 can also be adjusted according to actual performance requirements.

[0043] A protective cover 6 is installed above the array of superconducting coils 5. The protective cover 6 is made of non-metallic material to suppress eddy current losses caused by the mover magnetic field. The surface emissivity must be set to a large value to cool the constant conductor coils 4. A radiative heat shield 7 is installed on the protective cover 6. The radiative heat shield 7 cools the constant conductor coils 4 by radiation, eliminating the need for air or water cooling pipes. The temperature of the constant conductor coils 4 is controlled by controlling the emissivity of the radiative heat shield 7.

[0044] A moving element assembly is disposed between the protective cover 6 and the radiant heat shield 7. The moving element assembly includes a frame-shaped moving element support frame 2. In this embodiment, the moving element support frame 2 is a rectangular frame structure. The frame structure can also be circular or triangular, and the shape of the frame structure can be adjusted according to the actual situation. It can also be an irregular shape. At least one set of constant conductor coils 4 is disposed within the frame structure. Each set of constant conductor coils 4 includes at least two constant conductor coils 4, such as... Figure 3 As shown, in this embodiment, three constant conductor coils 4 form a group of three-phase constant conductor coils 4. The constant conductor coils 4 are racetrack-shaped. The four groups of three-phase constant conductor coils 4 are placed within a rectangular frame structure, and the constant conductor coils 4 in adjacent three-phase constant conductor coils 4 are on the same plane and perpendicular to each other. Each group of three-phase constant conductor coils 4 is supplied with an alternating current with a phase difference of 120 degrees. The number of constant conductor coils 4 in each group can be adjusted according to actual conditions, for example, two-phase or four-phase, etc. An alternating current with a phase difference of 90 degrees is supplied to the two-phase constant conductor coils 4 and the four-phase constant conductor coils 4.

[0045] The air gap length of a conventional semi-superconducting motor is 12 mm, while the air gap length of this embodiment is 2 mm.

[0046] A design method for a low-loss superconducting motor, the specific steps of which are as follows:

[0047] Step S1: Calculate the stator magnetic field based on the actual required acceleration.

[0048] The superconducting coils 5 are arranged periodically at a spacing of 2τ. The magnetic field generated by the array of superconducting coils 5 has an amplitude of B. s A fundamental wave with a period of 2τ has an amplitude of I. m A current with a phase angle of φ flows through a set of three-phase coils in the rotor support frame 2, and the electromagnetic force (F) acting on it... x F z )as follows:

[0049] F x =(3 / 2)KI m sin(φ)

[0050] F z =-(3 / 2)KI m cos(φ)(1)

[0051] The formula for the force constant K is as follows:

[0052]

[0053] α=πb m / 2τ,L m b m N m as well as These are the length, width, number of turns, and fill factor of the constant conductor coil 4 on the mover support frame 2, respectively;

[0054] The force generated by the motor and the stator magnetic field B of the superconductor coil 5 s And the current I of the constant conductor coil 4 m Proportional;

[0055] Based on the number and arrangement of the three-phase coils on the mover assembly, the relationship between the table acceleration and the force generated by the motor is as follows;

[0056] F x =MA x / 2F z =Mg / 4(3)

[0057] Among them, A x Let g be the acceleration of the worktable in the x-direction, g be the acceleration due to gravity, and M be the mass.

[0058] According to the acceleration A of the workbench x Determine the stator magnetic field B s and the current I of the constant conductor coil m .

[0059] Currently, widely used planar motors generally use permanent magnets from Halbach arrays instead of superconducting magnets, with the stator magnetic field B... s =0.6T. Assume I m =25A(≡I0), N m =300, then the stage acceleration Ax = 8G. This is equivalent to the acceleration of the wafer stage in a modern exposure system.

[0060] like Figure 5 As shown, for a constant conductor coil current I m =0.5I0,0.7I0,0.8I0, calculate the stator magnetic field required to achieve the table acceleration (16G to 32G) according to formulas (1) to (3).

[0061] Compared to conventional motors, the stator and rotor assemblies proposed in this embodiment have smaller air gap lengths, thus making it easier to increase the stator magnetic field B proposed in this embodiment. s .

[0062] Step S2: Calculate the current of the superconductor coil 5 based on the stator magnetic field.

[0063] Stator magnetic field (B) x B z The calculation formula for ) is as follows:

[0064]

[0065] The function to be integrated is as follows:

[0066] f x (R, Z, θ) = Aξ + xξ 2 ln(A+K)

[0067] in,

[0068] C=Zz J s =N s I s / (b s H s η = sinθ ξ = cosθ

[0069] K = R - xξ R1 = D s / 2-b s R2=D s / 2 Z2=H s / 2 Z1=-H s / 2

[0070] The current in the superconducting coil is I. s μ0 is the permeability of free space, N s D is the number of turns. s b is the outer diameter s H is the width. s For height. Compared with conventional motors, the air gap length between the stator assembly and the mover assembly proposed in this embodiment is smaller, such as Figure 6 As shown in the graph, the relationship between the current in the superconducting coil 5 and the stator magnetic field can be seen from the graph. This embodiment proposes that the stator magnetic field can be generated with a relatively small superconducting current.

[0071] Step S3: Calculate the critical current and superconductor temperature based on the current in superconductor coil 5.

[0072] The critical current is the maximum value of the current in superconductor coil 5. It is a function of the temperature T around superconductor coil 5, the magnitude |B| of the magnetic field, and its direction φ. This embodiment uses an interpolation function obtained from existing data for calculation. The interpolation function is: To suppress AC losses, a critical current I is assumed. c Stator coil current Is Much larger, is represented by I. c =K s I s K s For safety reasons, in this embodiment K s Take 2.

[0073] The formula for calculating the temperature of a superconductor is as follows:

[0074]

[0075] Among them, T s V is the temperature at which a superconductor is formed. s This refers to the region of a superconducting coil.

[0076] The relationship between the temperature and current of a superconducting coil, such as... Figure 7 As shown, the cooling capacity of a cryogenic cooler decreases as the temperature decreases, such as... Figure 8 As shown, the temperature of the superconducting coil 5 is therefore set between 20K and 45K. If a single-stage refrigerator with a large cooling capacity can be used within this temperature range, this increases the advantage of superconducting magnets over permanent magnets.

[0077] like Figure 9 As shown, the relationship between the stage acceleration and the superconductor coil temperature is illustrated, indicating that when I... m When I > 0.5I0, the superconducting motor proposed in this invention can achieve a greater table acceleration than conventional motors. m The difference is particularly noticeable when the value is 0.7I0 or higher.

[0078] This embodiment uses a single-stage GM chiller to cool the motor.

[0079] Step S4: Determine the cooling system based on the superconductor temperature.

[0080] The internal thermal analysis model of the motor in this embodiment is as follows: Figure 10 As shown, the interior consists of N planes, where N = 12 in the diagram.

[0081] Step S41: Calculate the heat transfer, which includes radiative heat transfer, conductive heat transfer, and wire heat transfer.

[0082] The radiative heat transfer on each plane is q = [q1, q2, ... q N ] T The calculation formula is as follows:

[0083] q = RP -1 S

[0084]

[0085] Where, ε i and T i Let F be the emissivity and temperature of plane i, respectively, σ be the Boltzmann constant, and F be the temperature of plane i. ij Let T be the shape factor from plane i to plane j. 10 =T 11 =T 12 =T H (Room temperature)

[0086] The heat transfer of the legs and base of the stator support frame 3 is Q1 and Q3, respectively, and the heat transfer of the sides and top of the radiant heat shield 7 is Q5 and Q6, respectively. The calculations are as follows:

[0087]

[0088] Among them, A Leg A Cover A Shield and A Ceil These are representative cross-sections of the side and top surfaces of the three legs of the stator support frame, the protective cover 6, and the radiant heat shield 7. Base T Cover T Shield And T Ceil These represent the temperatures of the base of the stator support frame 3, the protective cover 6, and the sides and top of the radiant heat shield 7, respectively. Additionally, Kg10 represents the thermal conductivity of material G10.

[0089] The heat transfer Q on the upper and lower surfaces of each superconductor coil 5 u and Q L The calculation is as follows:

[0090]

[0091] Where, N Sup A represents the number of superconducting coils. Sup and A L T represents the area of ​​the top surface of the superconducting coil and the representative transverse cross-sectional area of ​​the base, respectively. L Superconductor temperature.

[0092] The heat transfer Q through the current-carrying wires between the vacuum wall and the radiant heat shield 7, and between the radiant heat shield 7 and the mover. S and Q V The calculations are as follows:

[0093]

[0094]

[0095] Where, N Forcer and N LeadsK represents the number of three-phase coils and wires, respectively. Cu and ρ Cu Let Q represent the thermal conductivity and resistivity of copper, respectively, and the heat transfer from the wire to the superconducting coil. W as follows:

[0096]

[0097] Step S42: Calculate the heat required for cooling based on the balance relationship of each heat transfer.

[0098] The balance relationship is as follows:

[0099] q3+N Sup Q U =0

[0100] Q5 + q2 + q8 = 0

[0101] Q6-Q s -Q v +q1+q7=0

[0102] Q3-Q5=0

[0103] Q1+Q3-q9-N Sup Q L =0

[0104] Q m -q4-q5-q6=0

[0105] The first three formulas above refer to the thermal balance on planes 3, 6, and 7, respectively. The fourth and fifth formulas represent the balance relationship around the bifurcation point of the protective cover and the base. The last formula represents the balance around the moving part.

[0106] The Joule heating of the moving coil is as follows:

[0107]

[0108] Among them, L c and S W These are the circumference of the coil and the cross-sectional area of ​​the coil wire, respectively. For I m The average value, T m The temperature of the mover. Furthermore, the thickness of the protective shield 6 is sufficiently small, therefore for simplicity, Q4 = 0.

[0109] The following assumptions were made regarding the temperature of each surface:

[0110] T1=T7=(T Ceil +T SHield ) / 2

[0111] T2=T8=(T Cover+T Shield ) / 2

[0112] T4 = T5 = T6 = T m

[0113] Solving for the unknown T using the equilibrium formula Ceil T Shield T3, T m T Base And T Cover To calculate the heat transfer.

[0114] Step S43: Determine the refrigeration system based on the heat required for cooling.

[0115] The formula for calculating the AC loss of superconductor coil 5 is as follows:

[0116]

[0117] Among them, Q AC For the AC loss of the superconducting coil, the external magnetic field provided by the moving coil is (B ex B ez ), V represents the frequency of the external magnetic field. SC The volume of the superconductor directly beneath the mover, V SC =N coil A coil H s ζ s , N coil and A coil Let B be the average velocity of the mover, the number of coils in the mover, and the projected area of ​​a single coil on the stator surface, respectively. Assume an external magnetic field B. ex and B ez The penetration field B is sufficiently smaller than that of the superconductor. px and B pz ;

[0118] B px =μ0(1-I s / I c )H px H px =I c / (2t tape )

[0119] B pz =μ0(1-I s / I c )H pz H pz =I c / (2H s ).

[0120] The calculation process for the external magnetic field of the constant conductor coil 4 is as follows:

[0121] The shape of the constant conductor coil 4 is generally racetrack-shaped, but for simplicity, let's assume it has a width of b. m rectangle (W) m ×L m ×H m ), the magnetic field around the coil (B) ex B ey B ez The calculation formula for ) is as follows:

[0122]

[0123]

[0124] The current density of the constant conductor coil 4 is The integration interval is defined as follows:

[0125] X1 = x + W m / 2X2=x+W m / 2-b m X3=xW m / 2+b m X4=xW m / 2

[0126] Y1=y+L m / 2Y²=Y+L m / 2-b m Y3 = yL m / 2+b m Y4=yL m / 2

[0127] Z1=z+H m / 2Z2=zH m / 2

[0128] like Figure 11 As shown, the integrand f is defined as follows:

[0129]

[0130] The heat Q required to cool the superconductor coil 5 c The calculation formula is as follows:

[0131] Q c =N sup ·(Q L +Q U )+Q W +Q AC

[0132] Based on the above calculations of heat transfer, the heat required to cool the superconductor coil 5 is less than the refrigeration capacity of the refrigerator to meet the cooling needs. The heat required to cool the superconductor coil 5 is Q. c The relationship with the temperature of the superconductor is as follows: Figure 12 As shown in the figure. It can be seen from the figure that Q c It has a cooling capacity less than that of a commercial single-stage refrigeration unit.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A low-loss superconducting motor, comprising a vacuum chamber, wherein a stator assembly and a mover assembly are disposed within the vacuum chamber, characterized in that: The stator assembly includes a stator support frame with a planar top structure. Several arrayed superconducting coils are arranged on the planar structure, with adjacent superconducting coils having different vertical polarities. The current of the superconducting coils is calculated based on the stator magnetic field. A protective cover is arranged above the arrayed superconducting coils, and a radiative heat shield is arranged on the protective cover. A mover assembly is arranged between the protective cover and the radiative heat shield. The mover assembly includes a frame-shaped mover support frame, within which at least one set of constant conductor coils is arranged. Each set of constant conductor coils includes at least two constant conductor coils. The temperature of the constant conductor coils is controlled by controlling the emissivity of the radiative heat shield, while the surface emissivity of the protective cover is used to cool the constant conductor coils. The critical current and superconductor temperature are calculated based on the current of the superconducting coils, and the cooling system is determined based on the superconductor temperature.

2. The low-loss superconducting motor according to claim 1, characterized in that: The planar structure is covered with multiple layers of insulating film to suppress radiant heat from the vacuum chamber.

3. The low-loss superconducting motor according to claim 1, characterized in that: The protective cover is made of non-metallic material.

4. A design method for a low-loss superconducting motor based on any one of claims 1-3, characterized in that, The specific steps are as follows: The specific steps are as follows: Step S1: Calculate the stator magnetic field based on the required acceleration; Step S2: Calculate the current in the superconductor coil based on the stator magnetic field; Step S3: Calculate the critical current and superconductor temperature based on the current in the superconductor coil; Step S4: Determine the cooling system based on the superconductor temperature; Step S4 is as follows: Step S41: Calculate the heat transfer, which includes radiative heat transfer, conductive heat transfer, and wire heat transfer. Step S42: Calculate the heat required for cooling based on the balance relationship of each heat transfer process; The formula for calculating the heat required for cooling is as follows: in, To cool the heat required by the superconductor coil, The number of superconducting coils, Heat is conducted to the lower surface of each superconducting coil. Heat is conducted to the upper surface of each superconducting coil. For heat transfer from the conductor to the superconducting coil, The superconducting coil loses heat through alternating current. Step S43: Determine the refrigeration system based on the heat required for cooling. The heat required to cool the superconductor coil is less than the refrigeration capacity of the refrigeration mechanism.

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