Low-loss superconducting motor and design method thereof

Abstract

The invention relates to the technical field of superconducting motors, in particular to a low-loss superconducting motor and a design method thereof.The low-loss superconducting motor comprises a vacuum chamber, a stator assembly and a mover assembly, and the stator assembly comprises a stator supporting frame with the top of a plane structure and a superconductor coil arranged on the plane structure; a protective cover is arranged above the superconductor coil, a radiant heat shielding cover is arranged on the protective cover, a mover assembly is arranged between the protective cover and the radiant heat shielding cover, the mover assembly comprises a mover supporting frame of a frame-shaped structure and a normal conductor coil, and the temperature of the normal conductor coil is controlled by controlling the emissivity of the radiant heat shielding cover. Meanwhile, the invention discloses a design method based on the low-loss superconducting motor, an air gap between the stator assembly and the rotor assembly is small, a high magnetic field is easy to achieve, Joule loss of the normal conductor coil is reduced, an air or water cooling pipeline is omitted, and temperature control is easy.

Description

[0001] This application is a divisional application of the following application: application date is October 14, 2024, application number is 202411433110.7, and the invention name is a low-loss superconducting motor and a design method thereof. TECHNICAL FIELD

[0002] The application relates to the technical field of superconducting motors, in particular to a low-loss superconducting motor and a design method thereof. BACKGROUND

[0003] The winding of the superconducting motor is a motor wound by practical superconducting wire, has the advantages of high power density and high efficiency, and is a promising motor. According to the structure, the superconducting motor is divided into a full superconducting motor and a half superconducting motor. In the full superconducting motor, the stator and the rotor are superconductors, and the stator and the rotor are installed in an ultra-low temperature constant temperature tank (vacuum chamber). The air gap between the stator and the rotor is small, and it is easy to achieve a high magnetic field. However, the superconductor coil for applying alternating current has a large loss, the rotor is difficult to rotate at a high speed in the ultra-low temperature constant temperature tank, and it is difficult to cool, so a complex mechanical or electrical system is needed to realize the safe operation of the motor. In the half superconducting motor, one of the stator and the rotor is a superconductor, and the other is a normal conductor. One of the stator and the rotor is installed in an ultra-low temperature constant temperature tank, and the other is installed outside the ultra-low temperature constant temperature tank. There is an ultra-low temperature constant temperature tank wall between the stator and the rotor. Therefore, the air gap between the stator and the rotor is large, and it is difficult to achieve a high magnetic field. The Joule loss caused by the alternating magnetic field still exists. SUMMARY

[0004] The purpose of the present application is to provide a low-loss superconducting motor and a design method thereof, which solves the above technical problems.

[0005] To achieve the above-mentioned purpose, the present application provides a low-loss superconducting motor, which comprises a vacuum chamber, a stator assembly and a rotor assembly arranged in the vacuum chamber, the stator assembly comprises a stator support frame with a planar structure, a plurality of arrayed superconductor coils are arranged on the planar structure, the vertical polarities of adjacent superconductor coils are different, a protective cover is arranged above the arrayed superconductor coils, a radiation heat shield is arranged on the protective cover, the rotor assembly is arranged between the protective cover and the radiation heat shield, the rotor assembly comprises a frame-shaped rotor support frame, at least one group of normal conductor coils is arranged in the frame-shaped rotor support frame, each group of normal conductor coils comprises at least two normal conductor coils, the temperature of the normal conductor coils is controlled by controlling the emissivity of the radiation heat shield, and the surface emissivity of the protective cover is used to cool the normal conductor coils.

[0006] Preferably, the planar structure is covered with a plurality of layers of thermal insulation film for inhibiting the radiation heat from the vacuum chamber.

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

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

[0009] The specific steps are as follows:

[0010] Step S1: calculating the stator magnetic field according to the actual required acceleration;

[0011] Step S2: calculating the current of the superconductor coil according to the stator magnetic field;

[0012] Step S3: calculating the critical current and superconductor temperature according to the current of the superconductor coil;

[0013] Step S4: determining the cooling system according to the superconductor temperature;

[0014] Step S4 is specifically:

[0015] Step S41: calculating the heat transfer amount, including radiation heat transfer amount, conduction heat transfer amount and wire heat transfer amount;

[0016] Step S42: calculating the required heat for cooling according to the balance relationship of each heat transfer amount;

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

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

[0019] Wherein, Q c is the required heat for cooling the superconductor coil, N sup is the number of superconductor coils, Q L is the conduction heat transfer amount of the lower surface of each superconductor coil, Q U is the conduction heat transfer amount of the upper surface of each superconductor coil, Q W is the heat transfer amount from the wire to the superconductor coil, and Q AC is the AC loss heat of the superconductor coil.

[0020] Step S43: determining the refrigeration system according to the required heat for cooling, and the required heat for cooling the superconductor coil is less than the refrigeration capacity of the refrigeration machine.

[0021] Therefore, the low-loss superconducting motor and the design method thereof have the beneficial effects that the air gap between the stator assembly and the rotor assembly is small, high magnetic field is easy to achieve, Joule loss of the normal conductor coil is reduced, air or water cooling pipes are saved, and temperature control is easy.

[0022] The technical solutions of the present application are described in further detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

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

[0024] Figure 2 A perspective view of a low-loss superconducting motor according to the present application;

[0025] Figure 3 A distribution diagram of a normal conductor coil of a low-loss superconducting motor according to the present application;

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

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

[0028] Figure 6 A graph showing the relationship between the current in the superconductor coil and the stator magnetic field;

[0029] Figure 7 A graph showing the relationship between the superconductor coil temperature and the superconductor coil current;

[0030] Figure 8 A graph showing the superconductor coil temperature design range;

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

[0032] Figure 10 A thermal analysis model diagram in a vacuum chamber;

[0033] Figure 11 A normal conductor coil analysis model diagram;

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

[0035] REFERENCE NUMERALS

[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, the embodiment 2 in the parent case also clearly indicates for a planar motor, and implicitly discloses that the mover support frame is linear motion, so the rotor part in the parent case is modified to the mover, the rotor coil is modified to the constant conductor coil, and the rotor magnetic field is modified to the mover magnetic field. The above modifications are all corresponding modifications of the original technical solution of the parent case, and do not exceed the scope of modification. DETAILED DESCRIPTION

[0038] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly used when the product is used, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "arrangement", "installation", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0039] The embodiments of the present application will be described in detail below with reference to the drawings.

[0040] Embodiment 1

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

[0042] The stator assembly includes a stator support frame 3 with a planar structure at the top, and a plurality of arrayed superconductor coils 5 are arranged on the planar structure, as shown in Figure 4 , the vertical polarity of adjacent superconductor coils 5 is different, the superconductor coils 5 are cylindrical coils with a height H s , the vertical polarity of adjacent superconductor coils 5 is different, i.e. N and S poles are arranged alternately, this embodiment is provided with 36 N poles and 25 S poles. The planar structure is covered with a plurality of layers of thermal insulation film for suppressing the radiant heat from the inner wall of the vacuum chamber 1 to maintain a low surface emissivity. And the stator support frame 3 is made of G10 material, which has the advantages of low thermal conductivity and relatively high rigidity, and the material of the stator support frame 3 can also be adjusted according to the actual performance.

[0043] The superconductor coil 5 is arranged above the array distribution, and a protective cover 6 is arranged above the superconductor coil 5, wherein the protective cover 6 is made of a non-metal material to inhibit eddy current loss caused by the magnet field. The surface emissivity must be set to a large value to cool the normal conductor coil 4. A radiation heat shield 7 is arranged on the protective cover 6, the radiation heat shield 7 cools the normal conductor coil 4 in a radiation cooling mode, and air or water cooling pipes can be omitted, and the temperature control of the normal conductor coil 4 is realized by controlling the emissivity of the radiation heat shield 7.

[0044] A magnet assembly is arranged between the protective cover 6 and the radiation heat shield 7, and the magnet assembly comprises a frame-shaped magnet support frame 2. In the embodiment, the magnet support frame 2 is a rectangular frame-shaped structure, and the frame-shaped structure can also be circular or triangular, and the shape of the frame-shaped structure can be adjusted according to actual conditions, and the frame-shaped structure can also be irregular. Figure 3 As shown in FIG. 2, three normal conductor coils 4 in the embodiment form a three-phase normal conductor coil 4, and the normal conductor coil 4 is in a racetrack shape. Four three-phase normal conductor coils 4 are arranged in the rectangular frame-shaped structure, and the normal conductor coils 4 in the adjacent three-phase normal conductor coils 4 are in the same plane and perpendicular to each other. An alternating current with a phase difference of 120 degrees is applied to each three-phase normal conductor coil 4. The number of normal conductor coils 4 in each three-phase normal conductor coil 4 can also be adjusted according to actual conditions, for example, two-phase or four-phase, and an alternating current with a phase difference of 90 degrees is applied to the two-phase normal conductor coil 4 and the four-phase normal conductor coil 4.

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

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

[0047] Step S1: calculating the stator magnetic field according to the actual required acceleration.

[0048] The superconductor coil 5 is arranged periodically with a spacing of 2τ, and the magnetic field generated by the array of the superconductor coil 5 is a fundamental wave with an amplitude of B s and a period of 2τ. An alternating current with an amplitude of I m and a phase angle of φ flows through a set of three-phase coils of the magnet support frame 2, and the electromagnetic force (F x , F z ) acting thereon is as follows:

[0049] F x =(3 / 2)KI m sin(φ)

[0050] F z =-(3 / 2)KI m cos(φ)(1)

[0051] where the force constant K is given by

[0052]

[0053] a = p b m / 2τ, L m , b m , N m and are the length, width, number of turns and filling factor of the normal conductor coil 4 on the mover support frame 2, respectively;

[0054] The force generated by the motor is proportional to the stator magnetic field B s of the superconductor coil 5 and the current I m of the normal conductor coil 4;

[0055] According to the number and arrangement of the three-phase coils on the mover assembly, the relationship between the worktable acceleration and the force generated by the motor is as follows:

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

[0057] where A x is the x-direction acceleration of the worktable, g is the acceleration of gravity, and M is the mass;

[0058] The stator magnetic field B x and the normal conductor coil current I s are determined according to the worktable acceleration A m .

[0059] The planar motor widely used at present generally uses Halbach array permanent magnets to replace superconducting magnets, and the stator magnetic field B s = 0.6T. Assuming I m = 25A (≡ I0), N m = 300, then the worktable acceleration Ax = 8G. This is equivalent to the acceleration of the wafer worktable in the modern exposure system.

[0060] As shown in Figure 5 , for the normal conductor coil current I m = 0.5I0, 0.7I0, 0.8I0, the stator magnetic field required to achieve the worktable acceleration (16G to 32G) is calculated according to formulas (1) to (3).

[0061] Compared with the conventional motor, the air gap length of the stator assembly and the mover assembly proposed in the embodiment is smaller, so it is easy to increase the stator magnetic field B s proposed in the embodiment.

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

[0063] The stator magnetic field (B x , B z ) is calculated 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] wherein,

[0068] C = Z - z 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] wherein, the current in the superconductor coil is I s , μ0 is the magnetic permeability of vacuum, N s is the number of turns, D s is the outer diameter, b s is the width, H s is the height. Compared with the conventional motor, the air gap length between the stator assembly and the mover assembly of the embodiment is smaller, as shown in the graph of the relationship between the current in the superconductor coil 5 and the stator magnetic field, it can be known that the stator magnetic field can be generated by a smaller superconducting current. Figure 6

[0071] Step S3: Calculate the critical current and superconductor temperature according to the current of superconductor coil 5.

[0072] The critical current is the maximum value of the current in the superconductor coil 5. It is a function of the temperature T around the superconductor coil 5, the magnetic field size |B| and the direction φ. The interpolation function obtained from the existing data is used for calculation in the embodiment, and the interpolation function is as follows: In order to suppress the alternating current loss, it is assumed that the critical current I c is greater than the stator coil current I​s is much larger, it is represented as I c =K s I s , K s is the safety factor, in this embodiment K s Take 2.

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

[0074]

[0075] Among them, T s is the superconductor temperature, V s is the region of the superconductor coil.

[0076] The relationship between the superconductor coil temperature and the superconductor coil current, such as Figure 7 As shown in Figure 2. The cooling capacity of the cryogenic cooler decreases as the temperature decreases, as shown in Figure 2. Figure 8 As shown, the temperature of the superconductor coil 5 is therefore set to 20 K to 45 K. 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 in the figure, the relationship between the workbench acceleration and the temperature of the superconductor coil is shown. m When I > 0.5I0, the superconducting motor proposed in the present invention can obtain a larger workbench acceleration than the traditional motor. m When the value is 0.7I0 or higher, the difference between the two is particularly obvious.

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

[0079] Step S4: Determine the cooling system according to the temperature of the superconductor.

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

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

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

[0083] q=RP -1 S

[0084]

[0085] Among them, ε i and T i are the emissivity and temperature of plane i, σ is the Boltzmann constant, F ij is the shape coefficient from plane i to plane j. 10 =T 11 =T 12 =T H (Room temperature).

[0086] The conduction heat transfer of the legs and base of the stator support frame 3 is Q1 and Q3, and the conduction heat transfer of the side and top surfaces of the radiant heat shield 7 is Q5 and Q6, which are calculated 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 stator support frame 3 legs, the protective cover 6, and the radiant heat shield 7. Base 、T Cover 、T Shield and T Ceil are the temperatures of the base of the stator support frame 3, the protective cover 6, and the side and top surfaces of the radiant heat shield 7. In addition, Kg10 represents the thermal conductivity of the material G10.

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

[0090]

[0091] Among them, N Sup represents the number of superconductor coils, A Sup and A L represent the area of ​​the top surface of the superconductor coil and the horizontal representative cross-sectional area of ​​the base, respectively. L Superconductor temperature.

[0092] The heat transfer Q between the vacuum wall and the radiation heat shield 7 and between the radiation heat shield 7 and the mover is S and Q V The calculations are as follows:

[0093]

[0094]

[0095] Among them, N Forcer and N LeadsK Cu and p Cu represent the thermal conductivity and resistivity of copper, respectively, the heat transfer amount Q W as follows:

[0096]

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

[0098] The balance 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 above first three equations indicate the heat balance on planes 3, 6, and 7, respectively, the fourth and fifth equations indicate the balance around the bifurcation point of the shield and the base, and the last equation indicates the balance around the mover,

[0106] The Joule heat of the mover coil is as follows:

[0107]

[0108] where L c and S W are the circumference of the coil and the cross-sectional area of the coil wire, respectively, is the average value of I m , and T m is the temperature of the mover. In addition, the thickness of the shield 6 is sufficiently small, and thus, for simplicity, Q4= 0.

[0109] The following assumptions are made for 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] Solve the unknown T by the balance equation Ceil , T Shield , T3, T m , T Base and T Cover to calculate each heat transfer.

[0114] Step S43: Determine the refrigeration system according to the heat required for cooling.

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

[0116]

[0117] Where Q AC is the AC loss of the superconducting coil, the external magnetic field provided by the mover coil is (B ex , B ez ), is the representative frequency of the external magnetic field, V SC is the volume of the superconductor directly below the mover, V SC =N coil A coil H s ζ s , N coil and A coil are the average speed of the mover, the number of coils of the mover and the projection area of a single coil on the stator surface respectively, it is assumed that the external magnetic fields B ex and B ez are small enough compared to the penetration fields B px and B pz of the superconductor respectively;

[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 external magnetic field of the normal conductor coil 4 is calculated as follows:

[0121] The shape of the normal conductor coil 4 is generally a racetrack shape, but for simplicity, it is assumed to be a rectangle (W m x L m x H m ) with a width of b m , and the calculation formula of the magnetic field (B ex , B ey , B ez ) around the coil is as follows:

[0122]

[0123]

[0124] The current density of the normal conductor coil 4 is The integration intervals are defined as follows:

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

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

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

[0128] As shown in Figure 11 , the definition of the integrand function f is as follows:

[0129]

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

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

[0132] The heat required for cooling the superconducting coil 5 is less than the refrigeration capacity of the refrigerator, i.e. Q c The relationship between the superconductor temperature and the heat required for cooling the superconducting coil 5 is shown in Fig. 2. Figure 12 As can be seen from the figure, Q c is less than the cooling capacity of a commercial single-stage refrigerator.

[0133] Finally, it should be noted that the above examples are only intended to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A low-loss superconducting motor, comprising a vacuum chamber, wherein a stator assembly and a mover assembly are arranged in the vacuum chamber, characterized in that: The stator assembly includes a stator support frame with a planar structure at the top, and a plurality of array-distributed superconductor coils are arranged on the planar structure. The vertical polarities of adjacent superconductor coils are different. A protective cover is provided above the array-distributed superconductor coils, and a radiation heat shielding cover is provided on the protective cover. A mover assembly is provided between the protective cover and the radiation heat shielding cover. The mover assembly includes a mover support frame with a frame-shaped structure, and at least one group of normal conductor coils is provided in the frame-shaped structure. Each group of normal conductor coils includes at least two normal conductor coils. The temperature of the normal conductor coils is controlled by controlling the emissivity of the radiation heat shielding cover, and the surface emissivity of the protective cover is set to cool the normal conductor coils.

2. A low-loss superconducting motor according to claim 1, characterized in that: The planar structure is covered with multiple layers of thermal insulation film to suppress radiant heat from within 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 according to any one of claims 1 to 3, characterized in that: The specific steps are as follows: The specific steps are as follows: Step S1: Calculate the stator magnetic field according to the actual required acceleration; Step S2: Calculating the current of the superconductor coil according to the stator magnetic field; Step S3: Calculating the critical current and the superconductor temperature according to the current of the superconductor coil; Step S4: determining a cooling system according to the temperature of the superconductor; Step S4 is specifically as follows: Step S41: Calculate the heat transfer, which includes radiation heat transfer, conduction heat transfer, and wire heat transfer; Step S42: Calculating the heat required for cooling based on the balance relationship of each heat transfer amount; The heat required for cooling is calculated as follows: Q c =N sup ·(Q L +Q U )+Q W +Q AC Among them, Q c The heat required to cool the superconductor coil, N sup is the number of superconductor coils, Q L The heat conducted to the lower surface of each superconductor coil, Q U For each superconductor coil, Q W is the heat transferred from the wire to the superconductor coil, Q AC The superconductor coil AC loses heat; Step S43: Determine a refrigeration system based on the amount of heat required for cooling. The amount of heat required to cool the superconductor coil is less than the refrigeration capacity of the refrigerator.

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