Superconducting motor and motor system

Abstract

This invention relates to a superconducting motor provided with a superconducting material in a motor rotor, and in particular, to a superconducting motor capable of rotating at a high-speed frequency, and to a driver or an inverter for driving the superconducting motor. This superconducting motor (1) is provided with a motor rotor (6) having a plurality of superconducting coils (5), and a motor stator (7) adjacent to the motor rotor (6). The motor stator (7) has teeth (20) composed of an amorphous substance, and windings (23) wound around the teeth (20).

Description

Superconducting motors and motor systems

[0001] The present invention relates to a superconducting motor having a superconducting material in the motor rotor, and more particularly to a superconducting motor capable of rotating at high frequencies, and a driver or inverter for driving the superconducting motor.

[0002] Motors are used in a wide range of fields, from household appliances to toys, electrical equipment for mobility, and drive equipment. ２ In response to the background of measures such as CO ２ Aerospace equipment and land mobility are seen as promising solutions, and there is a demand for small, highly efficient high-output motors.

[0003] Japanese Patent Application Laid-Open No. 2019-120399

[0004] In particular, permanent magnet motor technology has evolved with the advent of neodymium magnets and the development of improved BH products (energy products), as well as miniaturization, oxygen-free processing, Halbach arrays, and low-vibration orientation, all of which have promoted the miniaturization and high efficiency of permanent magnet motors. In this patent specification, miniaturization technology is essentially equivalent to high-efficiency technology. This is because achieving a 2x miniaturization and a √2x higher efficiency is the only way to achieve a heat balance.

[0005] One approach to miniaturization is to miniaturize the motor system as a whole, rather than the motor itself. In other words, the size of the motor itself is kept the same, and high efficiency is achieved by changing the rotational speed using a transmission mechanism such as a mechanical gear using planetary gears or helical gears, a magnetic gear, or an electric gear.

[0006] For example, when transmitting power to the drive wheels of electric mobility vehicles, the motor operates at low torque and high rotation speed, while the gears are used to reduce speed and torque, thereby reducing the current to the motor and reducing copper loss. In this case, rather than using a powerful magnet in the motor, bonded magnets, which have weaker magnetic force than sintered magnets, are used to reduce iron loss, or coreless motors, which have very little iron loss, are used. In some cases, motors are designed with six poles or less.

[0007] Conversely, there are also motors that reduce iron loss by using gears to increase speed and reduce torque, allowing the motor to rotate at a low speed with high torque. In this case, a multi-pole motor with at least six poles is often used to increase the motor frequency, and by reducing the length of the coil that protrudes from the core, the motor can be made smaller and lighter.

[0008] In both cases, we search for optimal calculation results based on calculations such as copper loss and iron loss for heat balance, and the high-frequency capability of the motor driver.

[0009] The present invention provides an electric motor capable of high-speed rotation and miniaturization, and related techniques.

[0010] In one aspect, a superconducting motor is provided, comprising: a motor rotor having a plurality of superconducting coils; and a motor stator adjacent to the motor rotor, the motor stator having teeth formed of a plurality of stacked amorphous plates and windings wound around the teeth. In one aspect, the windings include a bundle of a plurality of strands and an outer coating covering the bundle of a plurality of strands, each of the plurality of strands including a conductor and an inner coating covering the conductor, each of the plurality of strands having a cross-sectional area corresponding to a circular diameter of 0.71 mm or less. In one aspect, the thickness of the inner coating is 5 μm or less. In one aspect, the thickness of each of the plurality of amorphous plates is less than 0.3 mm. In one aspect, the motor stator includes an annular core positioned outside the teeth, the annular core being made of electromagnetic steel sheet. In one aspect, the motor rotor includes diodes connected in series to the plurality of superconducting coils. In one aspect, the motor rotor further includes resistors connected in series to the plurality of superconducting coils.

[0011] In one aspect, a motor system is provided comprising the superconducting motor, a plurality of inverters that supply variable frequency power to the superconducting motor, and a plurality of DC power supplies that apply voltages to the plurality of inverters, respectively. In one aspect, the motor system is provided comprising the superconducting motor, a power supply that supplies power to a plurality of superconducting coils of the superconducting motor, and a power line switching device arranged between the plurality of superconducting coils and the power supply, the power line switching device including a first power supply line, a first switch arranged on the first power supply line, a second power supply line connected in parallel to the first power supply line, a second switch and a resistor arranged on the second power supply line, and a switch control unit that controls operation of the first switch and the second switch, the switch control unit being configured to turn off the first switch and turn on the second switch when the superconducting motor is started, and then turn on the first switch and turn off the second switch after a predetermined time has elapsed.

[0012] In one aspect, the motor system further includes a capacitor disposed between the superconducting motor and the power line switching device, the capacitor being connected in parallel with the plurality of superconducting coils. In one aspect, the motor system further includes an auxiliary resistor disposed between the superconducting motor and the power line switching device, the auxiliary resistor being connected in parallel with the plurality of superconducting coils.

[0013] In one aspect, a motor system is provided comprising the superconducting motor, an inverter that supplies a variable frequency excitation current to a motor stator of the superconducting motor, and an inverter control unit that controls operation of the inverter, the inverter control unit being configured to issue a command to the inverter to periodically generate a pulse current to be superimposed on the excitation current. In one aspect, the motor system further comprises a voltage sensor that detects an induced voltage generated in the motor stator of the superconducting motor, the inverter control unit being configured to issue a command to the inverter to stop generating the pulse current when the induced voltage is higher than a predetermined upper limit value.

[0014] As long as the superconducting state of the superconducting coil is maintained, the electrical resistance of the superconducting coil is zero. This means that no loss occurs, and the direct current supplied to the superconducting coil continues to flow, behaving like a permanent magnet and supplying alternating magnetic flux to the motor stator. The motor stator teeth have a laminated structure made of amorphous material with high magnetic flux density. The combination of such a superconducting coil and amorphous teeth makes it possible to create an electric motor that is compact yet achieves high output.

[0015] 15A is a cross-sectional view showing an embodiment of a superconducting motor. FIG. 15B is a perspective view showing an embodiment of a motor rotor. FIG. 15C is a cross-sectional view taken along line A-A in FIG. 2. FIG. 15D is a schematic view showing an embodiment of a superconducting coil connection. FIG. 15E is a cross-sectional view showing an embodiment of a motor stator. FIG. 15F is a cross-sectional view showing an embodiment of a winding. FIG. 15G is a cross-sectional view showing an embodiment of a strand. FIG. 15G is a graph showing the relationship between the diameter of a conductor and the loss caused by heat generated by electrical resistance when a direct current flows through the conductor, and the relationship between the diameter of the conductor and the loss caused by eddy currents generated when an alternating current flows through the conductor. FIG. 15H is a graph showing the relationship between the diameter of the strand and the loss of the strand. FIG. 15A is a BMD diagram showing an embodiment of a method of winding a winding around teeth. FIG. 15B is a BMD diagram showing another embodiment of a method of winding a winding around teeth. FIG. 15C is a schematic view showing yet another embodiment of a method of winding a winding around teeth. FIG. 15D is a diagram explaining an embodiment of a method of creating a plurality of teeth from a flat plate by a punching process. FIG. 15E is a diagram explaining an embodiment of creating a plurality of teeth arranged in an annular shape by bending a stator core with a plurality of teeth created by a punching process. 1 is a cross-sectional view showing an embodiment of a dual radial type superconducting motor. FIG. 2 is a cross-sectional view showing an embodiment of an axial gap type motor. FIG. 3 is a cross-sectional view showing an embodiment of an axial gap type motor. FIG. 4 is a cross-sectional view showing an embodiment of a coreless motor. FIG. 5 is a view of an embodiment of a hollow type coreless motor as viewed from the axial direction. FIG. 6 is a view of another embodiment of a hollow type coreless motor as viewed from the axial direction. FIG. 7 is a cross-sectional view explaining an embodiment of an outer rotor type superconducting motor. FIG. 8 is a schematic view showing an embodiment of a motor system including a superconducting motor, two inverters for driving the superconducting motor, and two DC power supplies for supplying power to the two inverters. FIG. 9 is a schematic view showing another embodiment of a motor system including two inverters and two DC power supplies. FIG. 10 is a view showing an embodiment in which a chopper circuit is arranged between the power supplies and the inverters. FIG. 11 is a graph showing an embodiment of the control operation of the inverter. FIG. 11 is a schematic view showing an embodiment in which a superconducting motor is used as a drive source for a liquid fuel pump. FIG. 12 is a view showing an embodiment in which a superconducting motor is applied to a dry motor. FIG. 13 is a view showing an embodiment in which a superconducting motor is applied to a wet motor.FIG. 1 is a schematic diagram showing an embodiment of a motor system including a superconducting motor and a power supply system. FIG. 2 is a cross-sectional view showing an embodiment of a conductor constituting a superconducting coil. FIG. 3 is a schematic diagram showing another embodiment of a motor system including a superconducting motor and a power supply system. FIG. 4 is a schematic diagram showing an embodiment of a motor system including a superconducting motor. FIG. 5 is a diagram showing an example of an excitation current supplied from an inverter to a motor stator. FIG. 6 is a schematic diagram showing another embodiment of a motor system including a superconducting motor. FIG. 7 is a schematic diagram showing yet another embodiment of a motor system including a superconducting motor. FIG. 8 is a diagram showing an example of a pulse current superimposed on an excitation current.

[0016] Embodiments of the present invention will be described below with reference to the drawings. Fig. 1 is a cross-sectional view showing one embodiment of a superconducting motor. As shown in Fig. 1, the superconducting motor 1 includes a rotating shaft 2, a motor rotor 6 having a plurality of superconducting coils 5, and a motor stator 7 for generating a rotating magnetic field. The plurality of superconducting coils 5 are fixed to a rotor core 9 of the motor rotor 6. The motor rotor 6, including the plurality of superconducting coils 5 and the rotor core 9, is fixed to the rotating shaft 2 and rotates integrally with the rotating shaft 2. The superconducting motor 1 of this embodiment is a multi-pole electric motor with four or more poles.

[0017] The superconducting motor 1 further includes bearings 11 and 12 that rotatably support the rotating shaft 2, and a motor housing 15 to which the bearings 11 and 12 are fixed. The bearings 11 and 12 are arranged on both sides of the motor rotor 6 in the axial direction of the rotating shaft 2. The motor rotor 6, motor stator 7, and bearings 11 and 12 are arranged within the motor housing 15. The bearings 11 and 12 are ball bearings, and conductive oil is used to lubricate the balls of the bearings 11 and 12. In one embodiment, the balls of the bearings 11 and 12 are made of ceramic. The use of conductive oil or ceramic balls prevents galvanic corrosion.

[0018] The motor stator 7 is disposed adjacent to the motor rotor 6. The motor stator 7 includes a plurality of teeth (or pole teeth) 20, windings 23 wound around the teeth 20, and an annular core 24 disposed outside the plurality of teeth 20. The windings 23 are wound around the plurality of teeth 20 to form a plurality of coils. In the embodiment shown in FIG. 1 , the motor stator 7 is disposed radially outside the motor rotor 6 and surrounds the motor rotor 6. There is a radial gap between the motor rotor 6 and the motor stator 7. Such an electric motor is a radial gap type electric motor.

[0019] Fig. 2 is a perspective view showing one embodiment of the motor rotor 6, and Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2. The rotor core 9 has a plurality of protrusions 10 protruding radially outward, and a plurality of superconducting coils 5 are respectively held by these protrusions. More specifically, each superconducting coil 5 is made up of a superconducting wire wound around each protrusion 10. In this embodiment, six superconducting coils 5 are provided, but the number of superconducting coils 5 is not limited to this embodiment.

[0020] The superconducting coil 5 is connected to a DC circuit (not shown) and is disconnected from the DC circuit when the motor is running at the rated rotation speed. The superconducting coil 5 is cooled by a refrigerant such as liquid nitrogen cooled by a chiller (not shown). As a result, the superconducting coil 5 transitions to a superconducting state, and the resistance value of the superconducting coil 5 becomes zero. Therefore, no loss occurs, and the DC current supplied to the superconducting coil 5 continues to flow as long as the superconducting state of the superconducting coil 5 is maintained. The superconducting coil 5 behaves like a permanent magnet and supplies alternating magnetic flux to the motor stator 7.

[0021] FIG. 4 is a schematic diagram showing one embodiment of the wiring of the superconducting coils 5. As shown in FIG. 4, the winding directions of two adjacent superconducting coils 5 are opposite to each other to generate an alternating magnetic flux. Therefore, the number of superconducting coils 5 is an even number. The multiple superconducting coils 5 have magnetic poles in which N and S poles are arranged alternately. The polarity of the superconducting coils 5 can be maintained by constantly passing a direct current through the superconducting coils 5. Because of the DC superconductivity, a diode may be connected to the superconducting coils 5 to prevent reverse current. The superconducting coils 5 may be connected by a bus bar (not shown) or in series like a wave winding. It is also preferable that the superconducting coils 5 are connected by a superconducting conductor.

[0022] The protrusions 10 of the rotor core 9 may be made of either magnetic or non-magnetic material. If they are made of magnetic material, high torque is achieved due to the high magnetic permeability until the iron core is saturated. If they are made of non-magnetic material, hysteresis loss and eddy current loss caused by the iron core do not occur, so high efficiency and high quality can be expected.

[0023] Power may be supplied to the superconducting coil 5 by a non-contact power supply. An electromagnetic induction or magnetic resonance mechanism may be provided at the end of the superconducting coil 5, or a harmonic magnetic field may be applied to the motor stator 7 to generate an induced voltage in the superconducting coil 5 due to changes in the magnetic field, and this voltage may be used as the excitation voltage. In this case, a diode is required to prevent backflow. Also, like an induction machine, the motor rotor 6 may be treated as a squirrel-cage rotor.

[0024] FIG. 5 is a cross-sectional view showing one embodiment of a motor stator 7. As shown in FIG. 5, the motor stator 7 has T-shaped teeth 20 (also called pole teeth) that form slots 21 for winding the windings 23. These teeth 20 serve to more effectively circulate magnetic flux from the motor rotor 6. The motor stator 7 includes an annular core 24 disposed outside the teeth 20. The windings 23 are wound around the teeth 20 to form multiple coils. The motor stator 7 and windings 23 in FIG. 5 employ a so-called concentrated winding configuration. In an inner-rotor type radial gap electric motor, the annular core 24 is disposed radially outside the teeth 20.

[0025] In this embodiment, the tooth 20 is made up of a plurality of stacked amorphous plates, each of which has a thickness of less than 0.3 mm (preferably 0.2 mm or less, more preferably 0.1 mm or less). In one embodiment, the thickness of each of the plurality of amorphous plates is 0.025 mm to 0.035 mm.

[0026] The annular core 24 is formed of a laminated structure of multiple electromagnetic steel plates made of alloy steel containing silicon. The thickness of the electromagnetic steel plates is greater than the thickness of the amorphous plates, for example, 0.35 mm. In one embodiment, the teeth 20 and the annular core 24 may be integrally formed to form a stator core. In this case, the stator core including the multiple teeth 20 has a laminated structure of multiple amorphous plates.

[0027] The tooth 20 made of amorphous has a configuration that satisfies the relationship B50×Ast>Br×Am, where B50 represents the magnetic flux density when the magnetizing force is 5000 A / mm, Ast represents the product of the width of the stator pole tooth 20 facing the superconducting coil 5 within an electrical angle of 180 and the axial length of the core, Br represents the residual magnetic flux density, and Am represents the product of Ast and the surface of the superconducting coil 5 facing it.

[0028] In one embodiment, the thickness of each of the stacked amorphous plates is less than 0.2 mm, and the magnetic flux density B50 is 1.5 T (Tesla) or more. In another embodiment, the thickness of each of the stacked amorphous plates is 0.1 mm or less, and the magnetic flux density B50 is 2.0 T (Tesla) or more.

[0029] When the magnetic flux generated by the motor rotor 6 is φm [Wb], it is appropriate to satisfy B50×Ast≧φm [Wb]. Alternatively, if the motor system is an axial gap system or the member is a powder magnetic core, it is appropriate to satisfy B100×Ast≧φm [Wb].

[0030] Amorphous materials have high magnetic permeability and a saturation magnetic flux density (Bs) that is approximately 20% lower than that of general electromagnetic soft iron. SST (single sheet magnetic measurement test) (JIS C 2556) was conducted on such amorphous materials using measurement samples measuring 30 mm wide x 120 mm long x 35 μm thick. When measuring B50 for such materials, magnetic flux exceeding Bs was measured. This is because Bs is reached below B50, and then the situation becomes similar to that of a coreless material, with magnetic flux increasing with the magnetic permeability of air. Such amorphous materials are preferred in the present invention, and it is desirable to use amorphous materials that reach Bs below B50, then increase magnetic flux with the magnetic permeability of air, and measure B50 ≥ 1.7 [T] as a test result. This means that magnetic flux densities exceeding those of electromagnetic steel sheets can be achieved in the magnetic flux range handled by typical superconducting motors of approximately 400 kW or less.

[0031] The windings 23 are wound in a distributed manner in the slots 21 of the motor stator 7. As a result, the winding factor of the motor is high because it is a full-pitch winding, which reduces the harmonic magnetic flux imparted to the motor rotor 6 and reduces losses in the motor components as a whole.

[0032] Figure 6 is a cross-sectional view showing one embodiment of the winding 23. As shown in Figure 6, the winding 23 is configured by twisting together a plurality of strands 40. The plurality of strands 40 are compressed to form a single bundle. Each of the plurality of strands 40 has a rectangular or square cross section, so there are almost no gaps between the strands 40.

[0033] The bundle of multiple strands 40 is covered with an insulating outer coating 42. The outer coating 42 is made of glass fiber or engineering plastic (e.g., PEEK or PPS). Because the winding 23 is made up of an assembly of multiple strands 40, the generation of eddy currents in each strand 40 is suppressed, thereby reducing eddy currents in the winding 23. Furthermore, twisting the multiple strands 40 minimizes parasitic inductance components and cancels out stray capacitance between adjacent strands 40.

[0034] As shown in FIG. 6 , the winding 23 has a rectangular cross section. Because the winding 23 can be treated as a rectangular wire, the space factor of the winding 23 in the slot 21 can be increased. In one embodiment, the space factor of the winding 23, excluding the outer coating 42, is 90% or more, where the cross-sectional area of ​​the winding 23 including its four corners is defined as 100%. In this embodiment, the motor stator 7 has a three-phase winding structure, but the winding structure is not limited to this embodiment. For example, the motor stator 7 may have a two-phase winding structure, a five-phase winding structure, or a seven-phase winding structure, or any other number of phases as long as it is a commercially available motor.

[0035] Fig. 7 is a cross-sectional view showing one embodiment of the wire 40. As shown in Fig. 7, the wire 40 has a quadrilateral cross section such as a rectangle or a square. The wire 40 has a conductor 45 and an inner coating 48, which is an insulating film that covers the conductor 45. The conductor 45 is made of a low-resistance material, such as aluminum, an aluminum alloy, copper, or carbon nanotubes (CNTs).

[0036] The inner coating 48 covers the entire outer surface of the conductor 45. Examples of materials for the inner coating 48 include oxide insulating materials, enamel resins made of polyamide-imide, polyimide, etc. Oxide insulating materials are preferred because they allow the inner coating 48 to be made thin. The inner coating 48 may have an air insulating layer with partial voids.

[0037] The thickness of the inner coating 48 of each wire 40 is 5 μm or less. In the case of an inner coating 48 made of enamel resin, the thickness of the inner coating 48 can be controlled to 1 to 3 μm, 3 to 5 μm, or the like, by adjusting the number of coats of enamel resin applied during the wire 40 manufacturing process. The wire 40 has a cross-sectional area equivalent to the cross-sectional area of ​​a circle with a diameter of 0.71 mm or less. The cross-sectional area of ​​the wire 40 is the overall cross-sectional area of ​​the wire 40, including the conductor wire 45 and the inner coating 48. In particular, as described below, the wire 40 has a cross-sectional area equivalent to the cross-sectional area of ​​a circle with a diameter of 0.126 mm to 0.71 mm.

[0038] 8 is a graph showing the relationship between the loss due to heat generated by electrical resistance when a DC current flows through the wire 40 (hereinafter referred to as DC loss) and the cross-sectional area of ​​the wire 40, and the relationship between the loss due to eddy current generated when an AC current flows through the wire 40 (hereinafter referred to as AC loss) and the cross-sectional area of ​​the wire 40. As can be seen from this graph, the larger the cross-sectional area of ​​the wire 40, the smaller the DC loss, while the larger the cross-sectional area of ​​the wire 40, the larger the AC loss. Therefore, there is a trade-off between DC loss and AC loss.

[0039] Therefore, in this embodiment, a wire 40 having a cross-sectional area that can reduce the total DC loss and AC loss is used. Fig. 9 is a graph showing the relationship between the diameter of a circle with a cross-sectional area equal to the cross-sectional area of ​​the wire 40 and the loss of the wire 40. The vertical axis represents the total DC loss and AC loss, and the horizontal axis represents the diameter of a circle with a cross-sectional area equal to the cross-sectional area of ​​the wire 40 including the conductor 45 and the inner coating 48.

[0040] In this graph, the strand 40 has an inner coating 48 with a thickness of 5 μm or less, which is a reliable and manufacturable insulating coating. The range of 0.126 mm to 0.71 mm is an effective size range for reducing total loss when subtracting the reduction in AC loss (loss due to eddy current) of the strand 40 from the increase in DC loss (loss due to heat generated by electrical resistance) of the strand 40. In one embodiment, the diameter of a circle with a cross-sectional area equal to the cross-sectional area of ​​the strand 40 is within the range of 0.2 mm to 0.71 mm.

[0041] The windings 23 are fixed with varnish or the like to prevent movement within the slots 21. In this embodiment, the windings 23 are fixed to the slots 21 with epoxy resin. The linear expansion coefficient relationship between the varnish, the inner coating 48 of the wire 40, and the outer coating 42 of the windings 23 is varnish > outer coating 42 > inner coating 48. This linear expansion coefficient relationship results in a gradual change in the linear expansion coefficient in the direction of transmission of heat generated by the motor rotor 6 or motor stator 7 or heat generated within the windings 23. This avoids dimensional changes due to sudden temperature changes, thereby preventing cracks and chips in the varnish, outer coating 42, inner coating 48, and motor stator 7.

[0042] The configuration employing the amorphous teeth 20 and windings 23 described above controls the d-axis and q-axis, enabling a large magnetic flux for the primary component. The low-loss amorphous teeth 20 minimize high-frequency loss, thereby minimizing iron loss, which would otherwise be caused by excessively large magnetic flux. The eddy current loss generated within the windings 23 due to the larger magnetic flux than before, which leaks into the windings 23 due to excessively large magnetic flux, can be reduced compared to conventional conductors. As a result, it is possible to select a larger number of poles and an inverter that operates at a higher frequency, achieving a smaller and lighter system overall.

[0043] FIG. 10 is a schematic diagram showing one embodiment of how the windings 23 are wound around the teeth 20. This embodiment shows how the windings 23 are wound for a 2-pole, 6-slot, full-pitch motor. This embodiment allows for good core material yield and an increased space factor. The teeth 20 may be separated from one another, or only the outer edges of the teeth 20 may be connected to one another. If only the outer edges of the teeth 20 are connected to one another, the structure of the teeth 20 is bent inward to form a cylindrical shape. If the teeth 20 are separated from one another, the teeth 20 are arranged in a circular pattern to form a cylindrical shape, and the teeth 20 are fixed in place using a jig (not shown) or an adhesive (e.g., varnish).

[0044] The width of the slots between the linearly arranged teeth 20 is larger than the width of the slots between the cylindrically arranged teeth 20, making it easy to arrange the windings 23. Pre-molded resin insulators or paper insulators may be placed between the windings 23, and an adhesive such as varnish may also be placed between the windings 23 to secure the windings 23 to the teeth 20. This ensures insulation of the windings 23 while protecting the insulating coating on the surface of the windings 23. Each slot is filled with a conductor or various insulating materials, mainly resin, which can produce various desirable effects such as improved thermal conductivity and conductor space factor (increased efficiency).

[0045] The symbols S1 to S7 (S1) in Figure 10 represent slot numbers. The winding 23 extends through the first layer of slot S1 and the second layer of slot S4, in that order, and then through the second layer of slot S7 (S1) and the second layer of slot S4, in that order. By connecting the windings in this manner, the current direction within the same slot can be made the same.

[0046] FIG. 11 is a schematic diagram showing one embodiment of how the winding 23 is wound around the teeth 20. This embodiment shows how the winding 23 is wound for a 4-pole, 12-slot full-pitch winding motor. The symbols S1 to S13 (S1) represent slot numbers. The winding 23 extends through the first layer of slot S1, the second layer of slot S4, the first layer of slot S7, and the second layer of slot S10, in that order, and further through the second layer of slot S13 (S1), the first layer of slot S10, the second layer of slot S7, and the first layer of slot S4, in that order. A bus bar may be used to connect slot S10 to slot S13 (S1).

[0047] In the embodiment shown in Figures 10 and 11, two turns are wound in each slot, but multiple turns, such as four, six, or eight turns, can also be wound in each slot in a similar manner. Figure 12 is a schematic diagram showing yet another embodiment of how the winding 23 is wound around the teeth 20. In this embodiment, there are four turns of the winding 23 per slot. As shown in Figure 12, two layers are created at a time. Since the winding 23 is created two at a time, in a winding with a number of layers that is a multiple of two, the 2n+1 layer and the 2n layer are connected. Current in and out appear in two layers.

[0048] 13 is a diagram illustrating one embodiment of a method for creating a plurality of teeth 20 from a flat plate by a punching process. In this punching process, a strip-shaped flat plate 36 is prepared, and two stator cores 37 are created from the flat plate 36, and each of the stator cores 37 has a plurality of teeth 20 connected linearly.

[0049] 14 is a diagram illustrating an embodiment in which a plurality of teeth 20 arranged in an annular shape are created by bending a stator core 37 having a plurality of teeth 20 created by a punching process. The stator core 37 having a plurality of linearly connected teeth 20 is sent to a spiral processing unit 38, and is deformed into a spiral shape by the spiral processing unit 38. In this way, a stator core 37 having a plurality of annular teeth 20 is created.

[0050] In one embodiment, the thin plate constituting the stator core 37 has a thickness of 0.3 mm or less. The thin plate material is either a material with a silicon content of 6.5% or an amorphous material with a Vickers hardness exceeding 1000. For this reason, conventional die designs are expected to be unable to punch through many plate materials successfully, significantly shortening the die's lifespan. Furthermore, the stress distribution generated in the plate material may cause cracks or chips in the plate material. Therefore, in the die used in this embodiment, the clearance between the punch and die during punching is set to less than 2 μm, and strict tolerance and temperature settings are established to concentrate the shear force.

[0051] 15A and 15B show BMD diagrams (Bending Moment Diagrams). In FIG. 15A, the clearance between the punch 200 and the die 201 is greater than 2 μm. In this case, the shear force generated in the thin plate 202 is widely distributed. As a result, the thin plate 202 is prone to cracking rather than being cut. Alternatively, sagging and burrs are likely to occur. In contrast, in FIG. 15B, the clearance between the punch 200 and the die 201 is less than 2 μm. In this case, the shear force generated in the thin plate 202 is concentrated at one point, allowing the punch 200 to cut the thin plate 202.

[0052] The above-described embodiment can also be applied to a dual-radial type superconducting motor shown in FIG. 16 . One embodiment shown in FIG. 16 has two motor rotors 6 arranged radially inside and outside a motor stator 7. The multiple superconducting coils 5 of the motor rotor 6 arranged radially inside the motor stator 7 are held by multiple protrusions 10 on the outer periphery of a rotor core 9. The multiple superconducting coils 5 of the motor rotor 6 arranged radially outside the motor stator 7 are held by multiple protrusions 10 on the inner periphery of a rotor housing 16. These two motor rotors 6 are connected to a rotating shaft 2 (see FIG. 1 ) and rotate together. In one embodiment, the superconducting coils 5 are arranged in a Halbach array.

[0053] The above-described embodiments can be applied not only to the radial gap motor shown in Fig. 1, but also to the axial gap motors shown in Fig. 17 and Fig. 18 and the coreless motor shown in Fig. 19. The embodiment shown in Fig. 17 has a motor rotor 6 adjacent to the motor stator 7 in the axial direction. The embodiment shown in Fig. 18 has two motor rotors 6 arranged on both sides of the motor stator 7 in the axial direction.

[0054] Figure 20 is a view of one embodiment of a hollow-type coreless motor as viewed from the axial direction. Configurations not specifically described are the same as those in the above-described embodiments, and therefore redundant description will be omitted. The superconducting motor 1 serving as a coreless motor of the embodiment shown in Figure 20 has an annular motor rotor 6 and an annular motor stator 7 surrounding the motor rotor 6. A plurality of superconducting coils 5 are held by a plurality of protrusions 10 on the outer periphery of the rotor core 9. The annular motor rotor 6 is disposed radially inside the motor stator 7.

[0055] Figure 21 is a view of another embodiment of a hollow-type coreless motor as viewed from the axial direction. Configurations not specifically described are the same as those of the above-described embodiments, and therefore redundant description will be omitted. The superconducting motor 1 serving as a coreless motor of the embodiment shown in Figure 21 has an annular motor rotor 6 and an annular motor stator 7 disposed radially inside the motor rotor 6. Multiple superconducting coils 5 are held by multiple protrusions 10 on the inner periphery of a rotor housing 16. The annular motor rotor 6 is disposed radially outside the motor stator 7 and surrounds it.

[0056] The above-described embodiment can also be applied to an outer rotor type superconducting motor described below. FIG. 22 is a cross-sectional view illustrating one embodiment of an outer rotor type superconducting motor. Configurations not specifically described are the same as those in the above-described embodiments, and therefore redundant description will be omitted. In the embodiment shown in FIG. 22 , the motor rotor 6 is disposed radially outside the motor stator 7. That is, the multiple superconducting coils 5 of the motor rotor 6 are arranged radially outside the multiple teeth 20 of the motor stator 7, and the multiple superconducting coils 5 are fixed to the inner circumferential surface of the rotor housing 16. The annular core 24 is disposed radially inside the multiple teeth 20.

[0057] The rotor housing 16 is fixed to the rotating shaft 2. Therefore, the rotor housing 16, the plurality of superconducting coils 5, and the rotating shaft 2 can rotate together. The motor stator 7 is fixed to a stator holder 17, which is fixed to the motor housing 15. The rotating shaft 2 extends through the stator holder 17.

[0058] Next, a description will be given of an embodiment of an inverter and a DC power supply that can operate the superconducting motor 1 of the above-mentioned embodiment with low loss. Fig. 23 is a schematic diagram showing an embodiment of a motor system that includes the superconducting motor 1 of the above-mentioned embodiment, two inverters 51, 52 that supply variable frequency power to the superconducting motor 1, and two DC power supplies 55, 56 that supply power to the two inverters 51, 52.

[0059] 23 , the motor system includes two inverters 51, 52 for driving the superconducting motor 1, and two DC power supplies 55, 56 electrically connected to the two inverters 51, 52 to apply voltage to the inverters 51, 52. The DC power supplies 55, 56 may be batteries. The inverters 51, 52 are provided with six semiconductor elements (or power elements) 58 on the positive side and six semiconductor elements (or power elements) 58 on the negative side to supply positive and negative currents to the U-, V-, and W-phase windings 23 of the superconducting motor 1.

[0060] The DC power supply 55 is connected to the inverter 51. More specifically, the positive electrode of the DC power supply 55 is connected to three semiconductor elements 58 on the positive electrode side of the inverter 51, and the negative electrode of the DC power supply 55 is connected to three semiconductor elements 58 on the negative electrode side of the inverter 51. The DC power supply 56 is connected to the inverter 52. More specifically, the positive electrode of the DC power supply 56 is connected to three semiconductor elements 58 on the positive electrode side of the inverter 52, and the negative electrode of the DC power supply 56 is connected to three semiconductor elements 58 on the negative electrode side of the inverter 52. A capacitor 61 for smoothing current is connected in parallel to the DC power supply 55, and a capacitor 62 for smoothing current is connected in parallel to the DC power supply 56.

[0061] The two DC power supplies 55, 56 have the same capacity [V]. For example, when a voltage of 800 V is applied to the superconducting motor 1, the two DC power supplies 55, 56 each have a capacity of 400 V. The semiconductor element 58 on the positive side of the inverter 51 is connected to the U-, V-, and W-phase windings of the superconducting motor 1. The semiconductor element 58 on the negative side of the inverter 51 is also connected to the U-, V-, and W-phase windings of the superconducting motor 1. Similarly, the semiconductor element 58 on the positive side of the inverter 52 is connected to the U-, V-, and W-phase windings 23 of the superconducting motor 1. The semiconductor element 58 on the negative side of the inverter 52 is also connected to the U-, V-, and W-phase windings 23 of the superconducting motor 1.

[0062] Three electric wires extending from the three output terminals of inverter 51 are joined with three electric wires extending from the three output terminals of inverter 52 to form three output electric wires 64, 65, and 66, respectively, and these three output electric wires 64, 65, and 66 are connected to the U-, V-, and W-phase windings 23 of superconducting motor 1, respectively. More specifically, a U-phase electric wire extending from the U-phase output terminal of inverter 51 and a U-phase electric wire extending from the U-phase output terminal of inverter 52 are joined to form U-phase output electric wire 64. A V-phase electric wire extending from the V-phase output terminal of inverter 51 and a V-phase electric wire extending from the V-phase output terminal of inverter 52 are joined to form V-phase output electric wire 65. A W-phase electric wire extending from the W-phase output terminal of inverter 51 and a W-phase electric wire extending from the W-phase output terminal of inverter 52 are joined to form W-phase output electric wire 66. The U-phase output wire 64, the V-phase output wire 65, and the W-phase output wire 66 are connected to the U-phase winding 23, the V-phase winding 23, and the W-phase winding 23, respectively, of the superconducting motor 1. Therefore, the combined power of the two inverters 51, 52 is supplied to the superconducting motor 1.

[0063] Hereinafter, the three semiconductor elements 58 on the positive side and the three semiconductor elements 58 on the negative side of each of the inverters 51 and 52 are each provided with a switching element 68 that can be turned on and off. The switching elements 68 are basically kept OFF. In this embodiment, taking into consideration the number of switching times, the switching elements 68 are configured from SiC semiconductor elements rather than relays.

[0064] In this way, even if inverter 51 becomes inoperable, voltages from two DC power sources 55, 56 can be supplied to inverter 52, and inverter 52 can apply a high voltage to superconducting motor 1. For this reason, semiconductor elements 58 of each inverter 51, 52 have a voltage resistance performance that can guarantee the total voltage of two DC power sources 55, 56. Also, each semiconductor element 58 is equipped with the same number of gate drivers as the number of semiconductor elements 58. The bus bars from DC power sources 55, 56 to each terminal have a multi-layer structure to reduce their parasitic impedance.

[0065] By using the inverters 51 and 52 configured in this manner, the low inductance of the wiring, including the bus bars, reduces the dV / dt characteristics, enabling operation with a short dead time and achieving a high carrier frequency. In one embodiment, the carrier frequency of each of the inverters 51 and 52 is 20 kHz or higher. By employing such a high carrier frequency, each of the inverters 51 and 52 can output smooth AC power.

[0066] Next, the control of this motor system will be described. The motor system is equipped with a control device 70 that controls the operation of inverters 51 and 52. This control device 70 controls the operation of inverters 51 and 52 using current sensors installed in inverters 51 and 52 and a rotation sensor mounted on rotating shaft 2 (see FIG. 1). That is, the control device 70 generates current commands using space vector control based on the d-axis, q-axis, and phase angle, and sends these current commands to inverters 51 and 52. The control device 70 generates the current commands using torque control that uses so-called PI control. PI control serves to correct for changes in conditions such as temperature.

[0067] A specific example of correction is correction of the difference in gain that occurs between the room temperature and the current temperature when the temperature of the superconducting motor 1 rises from room temperature to 100° C., causing a decrease in back electromotive force due to a decrease in magnetic flux. Also, in order to drive the superconducting motor 1 even when faced with a temporary loss of control due to a current sensor failing to read the current or a rotation sensor failing to read the rotation speed, the control device 70 has a function of ensuring control using a map prepared in advance based on the current command and operating status immediately before that.

[0068] The two inverters 51, 52 and two DC power supplies 55, 56 having the configuration shown in Fig. 23 are capable of controlling voltage. In other words, if the current to the superconducting motor 1 can be supplied by one of the two DC power supplies 55, 56, only one of the two DC power supplies 55, 56 operates, and if one of the two DC power supplies 55, 56 cannot supply the current, both DC power supplies 55, 56 operate.

[0069] In this way, the voltage is changed in stages to reduce voltage fluctuations, particularly during high current operation when iron loss becomes large, or during rated operation when the superconducting motor 1 is required to operate, thereby making it possible to reduce eddy current loss that occurs in the amorphous material and wires 40 (see Figures 6 and 7) of the superconducting motor 1.

[0070] In the embodiment shown in FIG. 23, two inverters 51 and 52 and two DC power supplies 55 and 56 are provided, but three or more inverters and corresponding three or more DC power supplies may be provided.

[0071] 24, two switches 73, 74 may be provided to electrically connect and disconnect the two inverters 51, 52. With this configuration, when one of the two inverters 51, 52 fails, the voltages of both DC power supplies 55, 56 can be applied to the other of the inverters 51, 52, thereby providing redundancy to the motor system.

[0072] In one embodiment, as shown in FIG. 25 , a chopper circuit 71 may be disposed between a DC power supply 55 and an inverter 51, and a chopper circuit 72 may be disposed between a DC power supply 56 and an inverter 52. The chopper circuits 71 and 72 are configured to control the DC voltage by switching (on / off) DC power using power semiconductor elements. The configurations of the chopper circuits 71 and 72 themselves are publicly known, so detailed description thereof will be omitted. The chopper circuits 71 and 72 aim to operate the inverters 51 and 52 at an optimal voltage. Specifically, the chopper circuits 71 and 72 provide a high voltage when the rotational frequency is high, thereby establishing a mode in which losses due to the rotational frequency and voltage alternating amplitude are high. In addition, the chopper circuits 71 and 72 provide a low voltage when the rotational frequency is low, thereby establishing a mode in which losses due to the rotational frequency and voltage alternating amplitude are low.

[0073] The magnitude of the voltage causes fluctuations in losses for the inverter due to the high switching voltage. The lower the voltage, the more the current fluctuations can be suppressed. For example, when generating a current of 150 Arms by alternating between 100 A and 200 A, the DC copper loss at 1 Ω is 30,000 W. In contrast, when controlling a current of 150 Arms at 150 A, the DC copper loss is 22,500 W. As can be seen from this example, suppressing current alternation at a lower voltage reduces copper loss in the inverter, motor, harness, etc., and can be expected to increase overall efficiency.

[0074] Iron loss and eddy current loss also occur depending on the magnitude of the magnetic flux. For example, when controlling a current fluctuating between 200A and 100A to create 150 Arms, if the winding inductance is 1[H] = 1[Wb / A], Δφ[Wb] is 100[Wb], resulting in hysteresis loss from the energy change in the hysteresis curve, or eddy current loss caused by a 100 Wb change in magnetic flux. If control can be maintained at 150A without fluctuation, Δφ[Wb] is 0, and there is zero change in magnetic flux, so no loss due to magnetic flux alternation occurs. In this way, operating the system at the optimal voltage and with as little voltage alternation as possible will lead to overall loss improvement.

[0075] 26 is a graph showing one embodiment of the control operation of the inverters 51 and 52. In one embodiment, the inverters 51 and 52 are configured to perform one-pulse control operation. The one-pulse control operation is a control operation that outputs a voltage with a pulse waveform of one cycle per one cycle of a sine wave. The pulse control operation can maximize the voltage utilization rate of the inverters 51 and 52.

[0076] FIG. 27 is a schematic diagram showing an embodiment in which a superconducting motor 1 is used as a drive source for a liquid fuel pump 80. The superconducting motor 1 is connected to the liquid fuel pump 80. An inverter 81 is disposed at a distance from the superconducting motor 1. As mentioned above, the superconducting motor 1 has a configuration that tends to have low inductance. This is due to the use of electromagnets made of superconductors with large magnetic flux. By using a strong electromagnet and operating the motor with a high power factor and low impedance, AC resistance can be reduced, making it possible to produce a large output of several hundred kilowatts or more at a voltage of approximately 100 to 1,000 V. This configuration inevitably reduces the number of turns in the windings of the superconducting motor 1, lowering the electrical time constant and creating problems such as the need to increase the carrier frequency for control.

[0077] In infrastructure pumps that require large output and mobility pumps that reach temperatures below -30°C, the inverter 81, battery 82, and superconducting motor 1 must operate in a temperature environment that is harsh for the operation of the power elements of the battery 82 and inverter 81. For this reason, insulation must be provided between the inverter 81 and the superconducting motor 1 that can operate in low-temperature or high-temperature environments.

[0078] 27 , a harness or electric wires 89 is arranged between the inverter 81 and the superconducting motor 1 to connect them. That is, the battery 82 and the inverter 81 are arranged in an electric room 85 separated from the superconducting motor 1. The superconducting motor 1 is connected to the inverter 81 by the harness or electric wires 89. In one embodiment, the inverter 81 may be a multi-inverter or dual inverter described with reference to FIGS. 23 to 25 . The superconducting motor 1 and the pump 80 are arranged in an explosion-proof area 86 that is independent from the electric room 85. The electric room 85 and the explosion-proof area 86 are located within a plant boundary 87. The superconducting motor 1 is connected to the pump 80 to drive the pump 80.

[0079] In this structure, the cooling of the battery 82 and inverter 81 can be performed separately from the cooling of the superconducting motor 1, and the temperature control of the battery 82 and inverter 81 can be performed independently from the temperature control of the superconducting motor 1. Furthermore, since there is a distance between the inverter 81 and the superconducting motor 1, the control of the inverter 81 is facilitated by the inductance of the electric wire 89. For example, for infrastructure motor control, by arranging the electric wire 89 preferably 80 m or more, an inductance of approximately 80 μH or more can be ensured, making it possible to easily control the inverter 81 by PWM of approximately 1000 V or less.

[0080] Figure 28 is a diagram showing an embodiment in which the superconducting motor 1 is applied to a dry motor. The pump device shown in Figure 28 includes the superconducting motor 1, a liquid pump 90 connected to the superconducting motor 1, and a shaft seal device 91 arranged between the superconducting motor 1 and the liquid pump 90. The liquid pump 90 includes a pump casing 92 and an impeller 93 arranged within the pump casing 92. The impeller 93 is connected to the rotating shaft 2 of the superconducting motor 1 and is rotated by the superconducting motor 1. The pump casing 92 has a suction port 94 and a discharge port 95 for the liquid. The suction port 94 of the liquid pump is immersed in the liquid, but the superconducting motor 1 is arranged above the liquid surface. Therefore, the superconducting motor 1 functions as a dry motor.

[0081] Figure 29 is a diagram showing an embodiment in which the superconducting motor 1 is applied to a wet motor. The pump device shown in Figure 29 is suitable for transporting liquefied gas. Examples of liquefied gas include liquid hydrogen, liquid helium, liquid methane, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas.

[0082] The pump device includes a suction vessel 109, which is a fluid vessel, and a superconducting motor 1 and a pump 110 disposed in the suction vessel 109. A small amount of heat from the ambient atmosphere of the pump device is transferred to the liquefied gas in the suction vessel 109. As a result, a portion of the liquefied gas is gasified to form boil-off gas (BOG) in the suction vessel 109. Therefore, the liquefied gas transfer system includes a boil-off gas discharge pipe 115 that discharges the boil-off gas from the suction vessel 109.

[0083] The pump device further includes a discharge pipe 116 connected to the discharge port of the pump 110 and extending to the outside of the suction vessel 109. The suction vessel 109 has a suction port 117 connected to its side wall. Liquefied gas is introduced into the suction vessel 109 through the suction port 117. During operation of the pump 110, the superconducting motor 1 and the entire pump 110 are immersed in the liquefied gas. Therefore, the superconducting motor 1 is a wet motor, and the pump 110 is a submersible pump that can operate in liquefied gas.

[0084] The pump 110 has a pump-side rotating shaft 120 connected to the rotating shaft 2, a bearing 121 that rotatably supports the pump-side rotating shaft 120, a plurality of impellers 125 fixed to the pump-side rotating shaft 120, and a pump casing 126 that houses the plurality of impellers 125. In one embodiment, the pump 110 may be provided with a single impeller 125.

[0085] When power is supplied to the superconducting motor 1 through a power cable (not shown), the superconducting motor 1 rotates the pump-side rotating shaft 120 and the impeller 125 together. As the impeller 125 rotates, the liquefied gas in the suction container 109 is sucked into the pump 110 through the suction port 127 of the pump 110 and is discharged into the discharge pipe 116.

[0086] Liquid gases such as liquid hydrogen, liquid helium, liquid nitrogen, liquid oxygen, and liquid methane are preferably cooled to 77 K (Kelvin) or below. The superconducting motor 1 is cooled by the cryogenic liquefied gas, and the superconducting motor 1 also reaches a cryogenic temperature. As a result, the superconducting coil 5 of the superconducting motor 1 can maintain its superconducting state. In the embodiment shown in Figure 29, the transport liquid and the cooling liquid can be the same, so there is no need to provide a cooling system for the superconducting coil 5, and the entire motor system can be made compact and lightweight.

[0087] Examples of materials for the superconducting coil 5 include the following. The temperature at which the material becomes a superconductor is indicated in parentheses. NbTi (9.5k) Nb ３ Sn(18k) MgB ２ (39k) Bi ２ Sr ２ Ca ２ Cu ３ O ｘ (110k) YBa ２ Cu ３ O ｘ (90k)

[0088] NbTi and Nb ３ Sn is preferable because it does not require a cooling system for the superconducting coil 5 when the temperature of the liquefied gas, such as liquid helium or liquid hydrogen, is relatively low. ２ , Bi ２ Sr ２ Ca ２ Cu ３ O ｘ , YBa ２ Cu ３ O ｘ is a so-called high temperature superconductor, and can become a superconductor at temperatures as low as 77K, the temperature of liquid nitrogen. The bearings 11, 12, and 121 in Fig. 29 may be plain bearings.

[0089] Fig. 30 is a schematic diagram showing one embodiment of a motor system including a superconducting motor 1 and a power supply system. In Fig. 30, only the motor rotor 6 of the superconducting motor 1 is depicted in schematic form, and other components such as the motor stator 7 are not shown. The superconducting motor 1 has the configuration of any of the above-described embodiments.

[0090] 30 , the motor system of this embodiment includes a superconducting motor 1, a power supply 150 that supplies power to the multiple superconducting coils 5 of the superconducting motor 1, and a power line switching device 151 that is arranged between the multiple superconducting coils 5 and the power supply 150. The power supply 150 is a DC power supply. When the superconducting motor 1 is in operation, the motor rotor 6 rotates, but the power supply 150 and the power line switching device 151 do not rotate. Therefore, a slip ring (rotary connector) 155 is provided between the motor rotor 6 and the power line switching device 151 to allow power from the power supply 150 to flow to the motor rotor 6.

[0091] The plurality of superconducting coils 5 when not in a superconducting state, i.e., the plurality of superconducting coils 5 in a normal conducting state, have a resistance R1. The power line switching device 151 includes a first power supply line 161, a first switch 162 arranged on the first power supply line 161, a second power supply line 164 connected in parallel to the first power supply line 161, a second switch 165 and a resistor 166 arranged on the second power supply line 164, and a switch control unit 167 that controls the operation of the first switch 162 and the second switch 165. The first power supply line 161 and the second power supply line 164 are electrically connected to the power supply 150 and the superconducting coils 5. The switch control unit 167 includes a memory 167a in which a program is stored and a processor 167b that executes operations according to instructions included in the program.

[0092] In one embodiment, as shown in FIG. 31 , the conductor constituting the superconducting coil 5 has a superconducting wire 170 made of a superconducting material and a superconducting coated conductor 171 covering the superconducting wire 170. The superconducting coated conductor 171 is made of a metal that is not a superconducting material, such as copper, silver, or aluminum. The superconducting coil 5 in a normal conducting state has a resistance R1 that includes the resistance of the superconducting wire 170 and the resistance of the superconducting coated conductor 171. When the superconducting coil 5 is cooled and enters a superconducting state, the resistance of the superconducting wire 170 becomes zero, and therefore, current flows through the superconducting wire 170 but not through the superconducting coated conductor 171.

[0093] The power line switching device 151 shown in Fig. 30 is provided to prevent a temperature rise in the superconducting coil 5 due to an inrush current when the superconducting motor 1 is started. That is, if a sudden change in current occurs when the superconducting motor 1 is started, this causes a sudden change in the magnetic flux, which generates an eddy current. If the superconducting coil 5 generates heat in excess of the cooling capacity of the cooling system, the temperature of the superconducting coil 5 may not be maintained. Furthermore, when an inrush current flows into the superconducting coil 5, the current flowing through the superconducting coil 5 may exceed the critical current, causing the superconducting coil 5 to lose its superconducting state.

[0094] Therefore, in this embodiment, in order to reduce the inrush current to the superconducting coil 5, the switch control unit 167 is configured to turn off the first switch 162 and turn on the second switch 165 when the superconducting motor 1 is started, and then turn on the first switch 162 and turn off the second switch 165 after a predetermined time has passed. When the first switch 162 is turned off and the second switch 165 is turned on, the current of the power supply 150 flows through the resistor 166. Therefore, the inrush current to the superconducting coil 5 is suppressed. When the first switch 162 is turned on and the second switch 165 is turned off after a predetermined time has passed (for example, a time in the range of 40 to 80 seconds), the current of the power supply 150 flows to the superconducting coil 5 through the first power supply line 161 without flowing through the resistor 166.

[0095] The motor system further includes a capacitor 175 disposed between the superconducting motor 1 and the power line switching device 151. This capacitor 175 is connected in parallel with the superconducting coil 5. The capacitor 175 smooths the current flowing through the superconducting coil 5 and can prevent a sudden excessive current from flowing through the superconducting coil 5.

[0096] Figure 32 is a schematic diagram showing another embodiment of a motor system including a superconducting motor 1 and a power supply system. The configuration of this embodiment that is not particularly described is the same as the embodiment described with reference to Figures 31 and 32, so duplicated description will be omitted. In this embodiment, the motor system further includes an auxiliary resistor 178 arranged between the superconducting motor 1 and the power line switching device 151.

[0097] The auxiliary resistor 178 is connected in parallel with the superconducting coil 5. The auxiliary resistor 178 has a resistance smaller than the resistance R1 of the superconducting coil 5 in a normal conducting state. Therefore, the current from the power supply 150 flows through the auxiliary resistor 178 and is consumed by the auxiliary resistor 178. This embodiment is advantageous when the superconducting state of the superconducting coil 5 is destroyed, when a quench occurs (when the coolant for cooling the superconducting coil 5 evaporates and generates a large amount of gas), or when it is simply desired to stop the superconducting motor 1 through which a large current is flowing.

[0098] 30 to 32 includes a power supply 150 that supplies power to the superconducting coils 5 of the motor rotor 6, but the embodiments described below do not include a power supply 150 for the motor rotor 6. Figure 33 is a schematic diagram showing an embodiment of a motor system including a superconducting motor 1. In this embodiment, power supplied from a power supply 180 (e.g., a commercial power supply) for the motor stator 7 is converted by an inverter 181 into variable-frequency three-phase AC power and supplied to the motor stator 7.

[0099] The motor rotor 6 is provided with diodes 183 connected to the multiple superconducting coils 5. The multiple superconducting coils 5 are connected in series, and the diodes 183 are connected in series to these superconducting coils 5. The diodes 183 rotate integrally with the multiple superconducting coils 5. The diodes 183 are provided to limit the direction of current flowing through the multiple superconducting coils 5 and to keep the direction of the magnetic field generated by each superconducting coil 5 constant.

[0100] FIG. 34 is a diagram showing an example of the excitation current supplied from the inverter 181 to the motor stator 7. The excitation current does not have a perfect sine wave due to the inductance, stray capacitance, etc. of the motor stator 7. That is, as shown in FIG. 34, the excitation current supplied to the motor stator 7 contains harmonic noise. Harmonic noise caused by disturbances in the excitation current flowing through the motor stator 7 causes positive and negative electromagnetic induction in the superconducting coil 5, which generates an induced current. The diode 183 restricts the flow of the excitation current to one direction, thereby making it possible to keep the direction of the magnetic field generated by the superconducting coil 5 constant. According to this embodiment, the power supply 150 for supplying power to the superconducting coil 5 can be eliminated.

[0101] Fig. 35 is a schematic diagram showing another embodiment of a motor system including a superconducting motor 1. The configuration of this embodiment that is not particularly described is the same as the embodiment described with reference to Fig. 33, so duplicated description will be omitted. In this embodiment, the motor rotor 6 further includes a resistor 185 in addition to a diode 183. The resistor 185 is connected in series to the multiple superconducting coils 5 and the diode 183. The diode 183 and the resistor 185 rotate integrally with the multiple superconducting coils 5.

[0102] Since the superconducting coil 5 theoretically has zero resistance, the induced current due to electromagnetic induction increases and may exceed the critical current. If the induced current flowing through the superconducting coil 5 exceeds the critical current, the superconducting coil 5 enters a normal conducting state. Therefore, the motor rotor 6 of the embodiment shown in Figure 35 is configured so that a portion of the induced current is consumed by a resistor 185. The motor rotor 6 configured in this manner can maintain the induced current flowing through the superconducting coil 5 constant near the critical current.

[0103] Figure 36 is a schematic diagram showing yet another embodiment of a motor system including a superconducting motor 1. The configuration of this embodiment that is not particularly described is the same as the embodiment described with reference to Figure 33, so duplicated description will be omitted. The motor system of this embodiment includes a superconducting motor 1, an inverter 181 that supplies a variable frequency excitation current to the motor stator 7 of the superconducting motor 1, and an inverter control unit 187 that controls the operation of the inverter 181.

[0104] The inverter control unit 187 includes a memory 187 a that stores a program and a processor 187 b that executes calculations in accordance with instructions contained in the program. The inverter control unit 187 is configured to issue a command to the inverter 181 to periodically generate a pulse current to be superimposed on the excitation current.

[0105] 37 is a diagram showing an example of a pulse current superimposed on the excitation current. As shown in FIG. 37, the inverter control unit 187 issues a command to the inverter 181 to periodically superimpose a pulse current P1 in synchronization with the sine wave frequency of the excitation current. This pulse current P1 causes electromagnetic induction in the superconducting coil 5, which then generates an induced current. By periodically generating such a pulse current P1, it is possible to periodically restore the magnetic force of the superconducting coil 5, which has been reduced due to current decay.

[0106] The motor system further includes a voltage sensor 190 that detects an induced voltage generated in the motor stator 7 of the superconducting motor 1. The voltage sensor 190 is connected to U-phase, V-phase, and W-phase power lines 191 that extend from the inverter 181 to the motor stator 7. The voltage sensor 190 is electrically connected to the inverter control unit 187, and the measured value of the induced voltage is sent from the voltage sensor 190 to the inverter control unit 187.

[0107] The induced voltage generated in the motor stator 7 varies depending on the induced current flowing in the superconducting coil 5. When the induced current flowing in the superconducting coil 5 exceeds the critical current, the superconducting coil 5 enters a normal conducting state. Therefore, when the induced voltage in the motor stator 7 detected by the voltage sensor 190 is higher than a predetermined upper limit, the inverter control unit 187 is configured to issue a command to the inverter 181 to stop generating the pulse current P1. Such operation of the inverter control unit 187 can prevent the induced current flowing in the superconducting coil 5 from exceeding the critical current.

[0108] The embodiment of resistor 185 described with reference to FIG. 35 can be applied to the embodiment described with reference to FIG.

[0109] When the harmonic noise contained in the excitation current to the motor stator 7 increases, the excitation force to the superconducting coil 5 increases. Therefore, in one embodiment, the winding factor of the motor stator 7 is set to a value other than 1, thereby increasing the harmonic noise contained in the excitation current to the motor stator 7. In other words, when the number of slots of the motor stator 7 within the range of one magnetic pole of the superconducting coil 5 is different from the number of phases, the winding factor of the motor stator 7 is set to a value other than 1.

[0110] Examples of winding factors of the motor stator 7 other than 1 under three-phase conditions include 4 poles and 6 slots, 4 poles and 24 slots, 8 poles and 48 slots, and 10 poles and 12 slots. Here, the number of poles is the number of superconducting coils 5 in the motor rotor 6, and the number of slots is the number of slots in the motor stator 7. In short-pitch winding, the pitch of the superconducting coil 5 differs from the pitch of the windings in the motor stator 7, so harmonic noise is likely to be included in the excitation current. Therefore, a motor stator 7 with short-pitch winding can increase the excitation force to the superconducting coil 5.

[0111] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims.

[0112] The present invention can be used in a superconducting motor having a superconducting material in the motor rotor.

[0113] REFERENCE SIGNS LIST 1 Superconducting motor 2 Rotating shaft 5 Superconducting coil 6 Motor rotor 7 Motor stator 9 Rotor core 10 Projection 11, 12 Bearing 15 Motor housing 16 Rotor housing 17 Stator holder 20 Teeth 23 Winding 24 Annular core 37 Stator core 40 Wire 42 Outer coating 45 Conductor 48 Inner coating 51, 52 Inverter 55, 56 DC power supply 58 Semiconductor element 61, 62 Capacitor 64, 65, 66 Output wire 68 Switching element 70 Control device 71, 72 Chopper circuit 73, 74 Switch 80 Liquid fuel pump 81 Inverter 82 Battery 85 Electrical room 86 Explosion-proof area 87 Plant boundary 89 Electric wire 90 Liquid pump 91 Shaft seal device 92 Pump casing 93 Impeller 94 Suction port 95 Discharge port 109 Suction vessel 110 Pump 115 Boil-off gas discharge pipe 116 Discharge pipe 117 Suction port 120 Pump-side rotating shaft 121 Bearing 125 Impeller 126 Pump casing 127 Suction port 150 Power supply 151 Power line switching device 155 Slip ring (rotary connector) 161 First power supply line 162 First switch 164 Second power supply line 165 Second switch 166 Resistor 167 Switch control unit 170 Superconducting wire 171 Superconducting coated conductor 175 Capacitor 178 Auxiliary resistor 180 Power supply 181 Inverter 183 Diode 185 Resistor 187 Inverter control unit 190 Voltage sensor

Claims

1. A superconducting motor comprising: a motor rotor having a plurality of superconducting coils; and a motor stator adjacent to the motor rotor, the motor stator having teeth formed from a plurality of stacked amorphous plates and windings wound around the teeth.

2. A superconducting motor as set forth in claim 1, wherein the winding comprises a bundle of a plurality of strands and an outer coating covering the bundle of the plurality of strands, each of the plurality of strands having a conductor and an inner coating covering the conductor, and each of the plurality of strands has a cross-sectional area corresponding to a circular diameter of 0.71 mm or less.

3. A superconducting motor according to claim 2, wherein the thickness of said inner coating is 5 μm or less.

4. The superconducting motor of claim 1, wherein the thickness of each of the plurality of amorphous plates is less than 0.3 mm.

5. A superconducting motor according to claim 1, wherein said motor stator has an annular core positioned outside said teeth, said annular core being made of electromagnetic steel sheet.

6. The superconducting motor of claim 1, wherein said motor rotor comprises diodes connected in series with said plurality of superconducting coils.

7. The superconducting motor of claim 6, wherein said motor rotor further comprises a resistor connected in series with said plurality of superconducting coils.

8. A motor system comprising: a superconducting motor according to any one of claims 1 to 7; a plurality of inverters that supply variable frequency power to said superconducting motor; and a plurality of DC power supplies that apply voltages to said plurality of inverters, respectively.

9. A motor system comprising: a superconducting motor according to any one of claims 1 to 5; a power supply that supplies power to a plurality of superconducting coils of said superconducting motor; and a power line switching device arranged between said plurality of superconducting coils and said power supply, said power line switching device comprising: a first power supply line; a first switch arranged on said first power supply line; a second power supply line connected in parallel to said first power supply line; a second switch and a resistor arranged on said second power supply line; and a switch control unit that controls operation of said first switch and said second switch, said switch control unit being configured to turn off said first switch and turn on said second switch when said superconducting motor is started, and to turn on said first switch and turn off said second switch after a predetermined time has elapsed.

10. The motor system according to claim 9, further comprising a capacitor disposed between the superconducting motor and the power line switching device, the capacitor being connected in parallel with the plurality of superconducting coils.

11. The motor system of claim 9, further comprising an auxiliary resistor disposed between the superconducting motor and the power line switching device, the auxiliary resistor being connected in parallel with the plurality of superconducting coils.

12. A motor system comprising: a superconducting motor according to claim 6 or 7; an inverter that supplies a variable frequency excitation current to a motor stator of said superconducting motor; and an inverter control unit that controls the operation of said inverter, wherein said inverter control unit is configured to give a command to said inverter to periodically generate a pulse current that is superimposed on said excitation current.

13. The motor system according to claim 12, further comprising a voltage sensor that detects an induced voltage generated in the motor stator of the superconducting motor, and the inverter control unit is configured to issue a command to the inverter to stop generating the pulse current when the induced voltage is higher than a predetermined upper limit value.

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