Method for operating a cryogenic refrigerator and cryogenic refrigerator

Abstract

The present invention aims to shorten the initial cooling time of a cryogenic refrigerator. The method for operating a cryogenic refrigerator (10) includes the following steps: connecting a second compressor (80) in series with a first compressor (12) on a high-pressure line (63) or a low-pressure line (64); connecting a buffer volume (70) to the low-pressure line (64) via a supply valve (72); in a state in which the second compressor (80) and the buffer volume (70) are connected to the cryogenic refrigerator (10), performing initial cooling of an expander (14) from an initial temperature to a cryogenic temperature; and subsequently performing steady-state operation of the expander at the cryogenic temperature after the initial cooling. The initial cooling includes the following steps: supplying working gas to the expander using the first compressor and the second compressor; and controlling the supply valve based on a measured pressure of the high-pressure line so that the pressure of the high-pressure line is maintained within a predetermined appropriate pressure range.

Description

[0001] This application claims priority based on Japanese Patent Application No. 2022-161835, filed on October 6, 2022. The entire contents of that Japanese application are incorporated herein by reference. Technical Field

[0002] This invention relates to an operating method of an ultra-low temperature refrigerator and the ultra-low temperature refrigerator itself. Background Technology

[0003] Cryogenic refrigerators are used to cool various objects such as superconducting equipment, measuring equipment, and samples used in cryogenic environments.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2020-112315

[0005] When using a cryogenic refrigerator to cool an object, the refrigerator must first be started to cool from its initial temperature to the target cryogenic temperature. This initial cooling process is also known as temperature reduction. Initial cooling is merely a preparatory step before cooling the object; therefore, it is desirable that the time required for this process be as short as possible. Summary of the Invention

[0006] One of the exemplary objectives of one embodiment of the present invention is to shorten the initial cooling time of the cryogenic refrigerator.

[0007] According to one embodiment of the present invention, a method for operating a cryogenic refrigerator is provided. The cryogenic refrigerator includes a first compressor, an expander, a high-pressure line connecting the first compressor to the expander, and a low-pressure line. The method includes the following steps: installing a second compressor on the high-pressure line or the low-pressure line and connecting it in series with the first compressor; connecting a buffer volume to the low-pressure line via a supply valve; performing initial cooling to cool the expander from an initial temperature to a cryogenic temperature while the second compressor and the buffer volume are connected to the cryogenic refrigerator; and performing steady-state operation of the expander at the cryogenic temperature after the initial cooling. Performing the initial cooling includes the following steps: supplying working gas to the expander using the first compressor and the second compressor; and controlling the supply valve according to the measured pressure of the high-pressure line to maintain the pressure of the high-pressure line within a preset appropriate pressure range.

[0008] According to one embodiment of the present invention, a method for operating a cryogenic refrigerator is provided. The cryogenic refrigerator includes a first compressor, an expander, a high-pressure line connecting the first compressor to the expander, and a low-pressure line. The method includes the following steps: connecting a second compressor in series with the first compressor on either the high-pressure line or the low-pressure line; performing initial cooling to cool the expander from an initial temperature to a cryogenic temperature while the second compressor is connected to the cryogenic refrigerator; and performing steady-state operation to maintain the expander at the cryogenic temperature after the initial cooling. The first compressor or the second compressor has a compressor motor with a variable operating frequency and is driven by the compressor motor. Performing the initial cooling includes the following steps: supplying working gas to the expander using the first compressor and the second compressor; and controlling the operating frequency of the compressor motor according to the measured pressure of the high-pressure line to maintain the pressure of the high-pressure line within a preset appropriate pressure range.

[0009] According to one embodiment of the present invention, a cryogenic refrigerator is provided, comprising: an expander capable of performing initial cooling from an initial temperature to a cryogenic temperature and subsequent steady-state operation to maintain the cryogenic temperature; a high-pressure line and a low-pressure line connected to the expander; a first pressure sensor for measuring the pressure of the high-pressure line; a second pressure sensor for measuring the pressure of the low-pressure line; a buffer volume for storing working gas; a supply valve connecting the buffer volume to the low-pressure line; and a controller configured to control the supply valve based on the pressure of the high-pressure line measured by the first pressure sensor during initial cooling, so as to maintain the pressure of the high-pressure line within a preset appropriate pressure range. The controller is further configured to: interrupt the control of the supply valve based on the pressure of the high-pressure line when the pressure of the low-pressure line measured by the second pressure sensor is lower than a preset low-pressure threshold, and control the supply valve based on the pressure of the low-pressure line measured by the second pressure sensor, so as to restore the pressure of the low-pressure line to the low-pressure threshold.

[0010] Furthermore, any combination of the above-mentioned constituent elements, or the substitution of the constituent elements of the present invention with each other in methods, apparatus, systems, etc., are also valid embodiments of the present invention.

[0011] According to the present invention, the initial cooling time of the cryogenic refrigerator can be shortened. Attached Figure Description

[0012] Figure 1 This is a diagram that schematically illustrates the cryogenic refrigerator according to the first embodiment.

[0013] Figure 2 This is a diagram that schematically illustrates the cryogenic refrigerator according to the first embodiment.

[0014] Figure 3This is a flowchart illustrating the control method of the cryogenic refrigerator according to the first embodiment.

[0015] Figure 4 This is a flowchart illustrating the control method of the cryogenic refrigerator according to the first embodiment.

[0016] Figure 5 This is a graph showing an example of temperature and pressure changes during the operation of the cryogenic refrigerator of the first embodiment.

[0017] Figure 6 In the diagram, (A) and (B) are graphs showing an example of pressure changes during operation of the cryogenic refrigerator of the first embodiment.

[0018] Figure 7 This is a graph showing an example of temperature and pressure changes during the operation of the cryogenic refrigerator of the first embodiment.

[0019] Figure 8 This is a diagram that schematically illustrates the cryogenic refrigerator according to the first embodiment.

[0020] Figure 9 This is a flowchart illustrating the control method of the cryogenic refrigerator according to the first embodiment.

[0021] Figure 10 This is a flowchart illustrating the control method of the cryogenic refrigerator according to the first embodiment.

[0022] Figure 11 This is a flowchart illustrating the control method of the cryogenic refrigerator according to the first embodiment.

[0023] Figure 12 This is a diagram that roughly illustrates the cryogenic refrigerator according to the second embodiment.

[0024] Figure 13 This is a diagram that roughly illustrates the cryogenic refrigerator according to the second embodiment.

[0025] Figure 14 This is a flowchart illustrating the operation method of the cryogenic refrigerator according to the second embodiment.

[0026] Figure 15 This is a diagram that schematically illustrates the cryogenic refrigerator according to the third embodiment.

[0027] Figure 16 This is a flowchart illustrating the operation method of the cryogenic refrigerator according to the third embodiment.

[0028] Figure 17This is a flowchart illustrating the operation method of the cryogenic refrigerator according to the third embodiment.

[0029] Figure 18 This is a diagram that schematically illustrates the cryogenic refrigerator according to the third embodiment.

[0030] Figure 19 This is a diagram that schematically illustrates the cryogenic refrigerator according to the third embodiment.

[0031] In the diagram: 10-Cryogenic refrigerator, 12-Compressor, 14-Expander, 54-First pressure sensor, 55-Second pressure sensor, 63-High pressure line, 64-Low pressure line, 70-Buffer volume, 72-Supply valve, 80-Second compressor, 82-Compressor motor, 110-Controller. Detailed Implementation

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same or equivalent constituent elements, components, and processes are labeled with the same symbols, and repeated descriptions are omitted where appropriate. For ease of explanation, scales or shapes of various parts are appropriately shown in the drawings, which are not intended to be limiting unless otherwise specified. The embodiments are illustrative and do not limit the scope of the invention in any way. All features or combinations thereof described in the embodiments are not necessarily essential to the invention.

[0033] Figure 1 and Figure 2 This is a schematic diagram illustrating the cryogenic refrigerator 10 according to the first embodiment. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator. Figure 1 The diagram schematically shows the control device 100 and the compressor 12 and expander 14 that constitute the cryogenic refrigerator 10. Figure 2 The internal structure of the expander 14 of the cryogenic refrigerator 10 is shown.

[0034] The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, pressurize the recovered working gas, and then supply it back to the expander 14. The compressor 12 and the expander 14 constitute the refrigeration cycle of the cryogenic refrigerator 10, thereby enabling the cryogenic refrigerator 10 to provide the desired cryogenic cooling. The expander 14 is also referred to as the cold head. The working gas is also referred to as the refrigerant gas, typically helium, but other suitable gases may also be used. For ease of understanding, in Figure 1 The arrows in the diagram indicate the direction of the working gas flow.

[0035] Furthermore, the pressure of the working gas supplied from compressor 12 to expander 14 and the pressure of the working gas returned from expander 14 to compressor 12 are typically much higher than atmospheric pressure, and can be referred to as the first high pressure and the second high pressure, respectively. For ease of explanation, the first high pressure and the second high pressure will also be simply referred to as high pressure and low pressure, respectively. Typically, the high pressure is, for example, 2 to 3 MPa. The low pressure is, for example, 0.5 to 1.5 MPa, for example, about 0.8 MPa. For ease of understanding, arrows are used to indicate the flow direction of the working gas.

[0036] The expander 14 includes a refrigeration cylinder 16 and a displacement assembly 18. The refrigeration cylinder 16 guides the displacement assembly 18 in linear reciprocating motion, and forms expansion chambers 32 and 34 for the working gas between the refrigeration cylinder 16 and the displacement assembly 18. Furthermore, the expander 14 includes a pressure switching valve 40, which determines the start time of supplying working gas to the expansion chambers and the start time of discharging working gas from the expansion chambers.

[0037] In this specification, to illustrate the positional relationships between the components of the cryogenic refrigerator 10, for convenience, the side closer to the top dead center of the axial reciprocating movement of the displacement device is labeled "upper," and the side closer to the bottom dead center is labeled "lower." The top dead center is the position where the displacement device has the largest volume of the expansion space, and the bottom dead center is the position where the displacement device has the smallest volume of the expansion space. During operation of the cryogenic refrigerator 10, a temperature gradient is generated from the upper axial direction downwards; therefore, the upper side can also be referred to as the high-temperature side, and the lower side as the low-temperature side.

[0038] The refrigeration unit cylinder block 16 includes a first cylinder block 16a and a second cylinder block 16b. As an example, the first cylinder block 16a and the second cylinder block 16b are cylindrical components, with the diameter of the second cylinder block 16b being smaller than the diameter of the first cylinder block 16a. The first cylinder block 16a and the second cylinder block 16b are coaxially arranged, and the lower end of the first cylinder block 16a is rigidly connected to the upper end of the second cylinder block 16b.

[0039] The displacement assembly 18 includes a first displacement 18a and a second displacement 18b connected together, which move integrally. As an example, the first displacement 18a and the second displacement 18b are cylindrical components, with the diameter of the second displacement 18b being smaller than the diameter of the first displacement 18a. The first displacement 18a and the second displacement 18b are coaxially arranged.

[0040] The first displacement device 18a is housed in the first cylinder block 16a, and the second displacement device 18b is housed in the second cylinder block 16b. The first displacement device 18a is capable of axial reciprocating along the first cylinder block 16a, and the second displacement device 18b is capable of axial reciprocating along the second cylinder block 16b.

[0041] like Figure 2 As shown, the first displacement device 18a houses the first cold storage device 26. The first cold storage device 26 is formed by filling the cylindrical main body of the first displacement device 18a with a metal wire mesh, such as copper, or other suitable first cold storage material. The upper and lower cover portions of the first displacement device 18a can be components different from the main body of the first displacement device 18a. The upper and lower cover portions of the first displacement device 18a can be fixed to the main body by appropriate methods such as fastening or welding, thereby accommodating the first cold storage material within the first displacement device 18a.

[0042] Similarly, the second displacement device 18b houses the second cold storage device 28. The second cold storage device 28 is formed by filling the cylindrical main body of the second displacement device 18b with a non-magnetic cold storage material such as bismuth, a magnetic cold storage material such as HoCu2, or other suitable second cold storage material. The second cold storage material can be formed in granular form. The upper and lower cover portions of the second displacement device 18b can be components different from the main body of the second displacement device 18b. The upper and lower cover portions of the second displacement device 18b can be fixed to the main body by appropriate methods such as fastening or welding, thereby accommodating the second cold storage material within the second displacement device 18b.

[0043] The displacement assembly 18 forms a chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the cryogenic cylinder 16. For heat exchange with the desired object or medium to be cooled by the cryogenic cryo-engine 10, the expander 14 includes a first cooling platform 33 and a second cooling platform 35. The chamber 30 is formed between the upper cover of the first displacement assembly 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower cover of the first displacement assembly 18a and the first cooling platform 33. The second expansion chamber 34 is formed between the lower cover of the second displacement assembly 18b and the second cooling platform 35. The first cooling platform 33 is fixed to the lower part of the first cylinder 16a surrounding the first expansion chamber 32, and the second cooling platform 35 is fixed to the lower part of the second cylinder 16b surrounding the second expansion chamber 34.

[0044] The first cold storage accumulator 26 is connected to the chamber 30 via a working gas flow path 36a formed on the upper cover of the first displacement device 18a, and is connected to the first expansion chamber 32 via a working gas flow path 36b formed on the lower cover of the first displacement device 18a. The second cold storage accumulator 28 is connected to the first cold storage accumulator 26 via a working gas flow path 36c formed from the lower cover of the first displacement device 18a toward the upper cover of the second displacement device 18b. Furthermore, the second cold storage accumulator 28 is connected to the second expansion chamber 34 via a working gas flow path 36d formed on the lower cover of the second displacement device 18b.

[0045] To prevent the working airflow between the first expansion chamber 32, the second expansion chamber 34, and the chamber temperature 30 from entering the gap between the refrigeration cylinder 16 and the displacement assembly 18 and thus into the first accumulator 26 and the second accumulator 28, a first seal 38a and a second seal 38b can be provided. The first seal 38a can be installed on the upper cover of the first displacement assembly 18a, positioned between the first displacement assembly 18a and the first cylinder 16a. The second seal 38b can be installed on the upper cover of the second displacement assembly 18b, positioned between the second displacement assembly 18b and the second cylinder 16b.

[0046] like Figure 1 As shown, the expander 14 has a refrigerator housing 20 that houses the pressure switching valve 40. The refrigerator housing 20 is combined with the refrigerator cylinder 16, thereby forming an airtight container that houses the pressure switching valve 40 and the displacement assembly 18.

[0047] like Figure 2 As shown, the pressure switching valve 40 is configured to have a high-pressure valve 40a and a low-pressure valve 40b, and to generate periodic pressure fluctuations within the refrigeration unit cylinder 16. The working gas outlet of the compressor 12 is connected to the chamber 30 via the high-pressure valve 40a, and the working gas inlet of the compressor 12 is connected to the chamber 30 via the low-pressure valve 40b. The high-pressure valve 40a and the low-pressure valve 40b are configured to selectively alternately open and close (i.e., while one valve is open, the other valve is closed).

[0048] The pressure switching valve 40 can also be a rotary valve. That is, the pressure switching valve 40 can also be configured to alternately open and close the high-pressure valve 40a and the low-pressure valve 40b by rotating and sliding the valve disc relative to the stationary valve body. In this case, the expander motor 42 can be connected to the pressure switching valve 40 in a way that rotates the valve disc of the pressure switching valve 40. For example, the pressure switching valve 40 can be configured such that the valve rotation axis is coaxial with the rotation axis of the expander motor 42.

[0049] Alternatively, the high-pressure valve 40a and the low-pressure valve 40b can be valves that can be controlled separately. In this case, the pressure switching valve 40 may not be connected to the expander motor 42.

[0050] The expander motor 42 is connected to the displacement drive shaft 44 via a motion conversion mechanism 43, such as an anti-rotation yoke mechanism. The expander motor 42 is mounted in the refrigerator housing 20. Similar to the pressure switching valve 40, the motion conversion mechanism 43 is also housed within the refrigerator housing 20. The motion conversion mechanism 43 converts the rotational motion output by the expander motor 42 into the linear reciprocating motion of the displacement drive shaft 44. The displacement drive shaft 44 extends from the motion conversion mechanism 43 toward the chamber 30 and is fixed to the upper cover of the first displacement device 18a. The rotation of the expander motor 42 is converted by the motion conversion mechanism 43 into the axial reciprocating motion of the displacement drive shaft 44, thereby causing the displacement assembly 18 to reciprocate axially within the refrigerator cylinder 16.

[0051] Furthermore, the expander 14 may also be equipped with a temperature sensor 46, which measures the temperature of the second cooling stage 35 (and / or the first cooling stage 33) and outputs a measured temperature signal representing the measured temperature.

[0052] The compressor 12 includes a high-pressure gas outlet 50, a low-pressure gas inlet 51, a high-pressure flow path 52, a low-pressure flow path 53, a first pressure sensor 54, a second pressure sensor 55, a bypass pipe 56, a compressor body 57, and a compressor frame 58. The high-pressure gas outlet 50 is located in the compressor frame 58 as the working gas discharge port of the compressor 12, and the low-pressure gas inlet 51 is located in the compressor frame 58 as the working gas intake port of the compressor 12. The high-pressure flow path 52 connects the discharge port of the compressor body 57 to the high-pressure gas outlet 50, and the low-pressure flow path 53 connects the low-pressure gas inlet 51 to the intake port of the compressor body 57. The compressor frame 58 houses the high-pressure flow path 52, the low-pressure flow path 53, the first pressure sensor 54, the second pressure sensor 55, the bypass pipe 56, and the compressor body 57. The compressor 12 is also referred to as a compressor unit.

[0053] The compressor body 57 is configured to internally compress the working gas drawn in from its inlet and discharge it from its outlet. The compressor body 57 can be, for example, a scroll pump, a rotary pump, or other pump that pressurizes the working gas. In this embodiment, the compressor body 57 is configured to discharge a constant flow rate of working gas. Alternatively, the compressor body 57 may be configured to allow a variable flow rate of the discharged working gas. The compressor body 57 is sometimes also referred to as a compression chamber.

[0054] The first pressure sensor 54 is disposed on the high-pressure flow path 52 to measure the pressure of the working gas flowing through the high-pressure flow path 52. The first pressure sensor 54 is configured to output a first measured pressure signal PH indicating the measured pressure. The second pressure sensor 55 is disposed on the low-pressure flow path 53 to measure the pressure of the working gas flowing through the low-pressure flow path 53. The second pressure sensor 55 is configured to output a second measured pressure signal PL indicating the measured pressure. Therefore, the first pressure sensor 54 and the second pressure sensor 55 can also be referred to as a high-pressure sensor and a low-pressure sensor, respectively. Furthermore, in this specification, either the first pressure sensor 54 or the second pressure sensor 55, or both, are sometimes referred to as "pressure sensors".

[0055] A bypass line 56 connects the high-pressure flow path 52 and the low-pressure flow path 53, allowing the working gas to bypass the expander 14 and return from the high-pressure flow path 52 to the low-pressure flow path 53. A safety valve 60 is provided on the bypass line 56 for opening and closing the bypass line 56 or controlling the flow rate of the working gas flowing through the bypass line 56. The safety valve 60 is configured to open when a pressure difference exceeding a set pressure acts between its inlet and outlet. The safety valve 60 can be an on / off valve or a flow control valve, for example, a solenoid valve. The set pressure can be appropriately set based on the designer's experience, experiments, or simulations. This prevents the pressure difference between the high-pressure line 63 and the low-pressure line 64 from exceeding the set pressure. Furthermore, it prevents the pressure in the high-pressure line 63 from becoming excessive.

[0056] Safety valve 60 can be configured to operate as a so-called safety valve, that is, to mechanically open when a pressure difference above a set pressure acts between the inlet and outlet. Alternatively, safety valve 60 can also be opened and closed under the control of control device 100. Control device 100 can control safety valve 60 by comparing the measured pressure difference between high-pressure line 63 and low-pressure line 64 with a set pressure, and opening safety valve 60 when the measured pressure difference is above the set pressure, and closing safety valve 60 when the measured pressure difference is below the set pressure. Control device 100 can obtain the measured pressure difference between high-pressure line 63 and low-pressure line 64 based on a first measured pressure signal PH from first pressure sensor 54 and a second measured pressure signal PL from second pressure sensor 55. As another example, control device 100 can also control safety valve 60 by comparing the measured pressure of high-pressure line 63 with an upper limit pressure based on the first measured pressure signal PH, and opening safety valve 60 when the measured pressure is above the upper limit pressure, and closing safety valve 60 when the measured pressure is below the upper limit pressure.

[0057] In addition, the compressor 12 may have various other components. For example, an oil separator, an adsorber, etc., may be provided on the high-pressure flow path 52. A storage tank and other components may be provided on the low-pressure flow path 53. Furthermore, an oil circulation system that uses oil to cool the compressor body 57 and a cooling system for cooling the oil may be provided on the compressor 12.

[0058] Furthermore, the cryogenic refrigerator 10 includes a gas pipeline 62 that circulates the working gas between the compressor 12 and the expander 14. The gas pipeline 62 includes a high-pressure pipeline 63 connecting the compressor 12 and the expander 14 to supply working gas from the compressor 12 to the expander 14, and a low-pressure pipeline 64 connecting the compressor 12 and the expander 14 to recover working gas from the expander 14 back to the compressor 12. A high-pressure gas inlet 22 and a low-pressure gas outlet 24 are provided on the refrigerator housing 20 of the expander 14. The high-pressure gas inlet 22 is connected to the high-pressure gas outlet 50 via a high-pressure piping 65, and the low-pressure gas outlet 24 is connected to the low-pressure gas inlet 51 via a low-pressure piping 66. The high-pressure pipeline 63 consists of the high-pressure piping 65 and the high-pressure flow path 52, and the low-pressure pipeline 64 consists of the low-pressure piping 66 and the low-pressure flow path 53. The bypass pipeline 56 can be considered part of the gas pipeline 62. The bypass line 56 connects the high-pressure line 63 and the low-pressure line 64 so that the working gas bypasses the expander 14 and flows back from the high-pressure line 63 to the low-pressure line 64.

[0059] Therefore, the working gas recovered from expander 14 to compressor 12 enters the low-pressure gas inlet 51 of compressor 12 from the low-pressure gas outlet 24 of expander 14 through low-pressure piping 66, and then returns to compressor body 57 via low-pressure flow path 53, where it is compressed and pressurized. The working gas supplied from compressor 12 to expander 14 exits from compressor body 57 through high-pressure flow path 52 and is discharged from high-pressure gas outlet 50 of compressor 12, and then is further supplied to expander 14 via high-pressure piping 65 and high-pressure gas inlet 22 of expander 14.

[0060] Furthermore, the cryogenic refrigerator 10 includes a buffer volume 70, a supply valve 72, and a recovery valve 74. The buffer volume 70 is a volume used to store the working gas; for example, it can be a buffer tank. The supply valve 72 connects the buffer volume 70 to the low-pressure line 64, and the recovery valve 74 connects the buffer volume 70 to the high-pressure line 63. The supply valve 72 and the recovery valve 74 can be on / off valves or flow control valves; for example, they can be solenoid valves.

[0061] During periods when the cryogenic refrigerator 10 is not in operation, the pressure of the buffer volume 70 becomes the sealing pressure of the working gas sealed in the cryogenic refrigerator 10. During periods when the cryogenic refrigerator 10 is in operation (e.g., during initial cooling or steady-state operation), the pressure of the buffer volume 70 becomes the intermediate pressure between the pressure of the high-pressure line 63 and the pressure of the low-pressure line 64 (e.g., the average pressure of the high and low pressures).

[0062] Therefore, during the operation of the cryogenic refrigerator 10, if the supply valve 72 is opened, the working gas is supplied from the buffer volume 70 to the low-pressure line 64 after passing through the supply valve 72. If the supply valve 72 is closed, the supply of working gas from the buffer volume 70 to the low-pressure line 64 is stopped. Furthermore, if the recovery valve 74 is opened, the working gas is recovered from the high-pressure line 63 to the buffer volume 70 after passing through the recovery valve 74. If the recovery valve 74 is closed, the recovery of working gas from the high-pressure line 63 to the buffer volume 70 is stopped. Thus, by opening and closing the supply valve 72 and the recovery valve 74, the amount of working gas circulating in the gas line 62 can be adjusted, and consequently, the pressures of the high-pressure line 63 and the low-pressure line 64 can also be controlled.

[0063] like Figure 1 As shown, the control device 100 for controlling the cryogenic refrigerator 10 includes a controller 110 that controls the supply valve 72 and the recovery valve 74. The controller 110 is electrically connected to a first pressure sensor 54 and a second pressure sensor 55 to acquire a first measured pressure signal PH and a second measured pressure signal PL. As explained later, the controller 110 is configured to receive the first measured pressure signal PH from the first pressure sensor 54 and open / close the supply valve 72 and the recovery valve 74 based on the measured pressure of the high-pressure line 63 displayed by the first measured pressure signal PH. Furthermore, the controller 110 is electrically connected to a temperature sensor 46 to acquire a measured temperature signal from the temperature sensor 46.

[0064] In the illustrated example, the control device 100 is separately installed and connected to the compressor 12 and expander 14, but it is not limited to this. The control device 100 may also be mounted on the compressor 12. The control device 100 may also be mounted on the expander motor 42, etc. (i.e., mounted on the expander 14). The controller 110 may also be mounted on the supply valve 72 or the recovery valve 74, or may be mounted on the supply valve 72 and the recovery valve 74 respectively.

[0065] The control device 100 is implemented in terms of hardware structure through components or circuits, such as a computer's CPU or memory, and in terms of software structure through computer programs, etc. Figure 1The functional blocks implemented through their cooperation are appropriately depicted. Those skilled in the art will understand that these functional blocks can be implemented in various forms through a combination of hardware and software.

[0066] During the operation of compressor 12 and expander motor 42, the cryogenic refrigerator 10 generates periodic volume changes and synchronous pressure changes of the working gas in the first expansion chamber 32 and the second expansion chamber 34. Typically, in the intake process, by closing the low-pressure valve 40b and opening the high-pressure valve 40a, high-pressure working gas flows from compressor 12 through high-pressure valve 40a into chamber 30, and is supplied to the first expansion chamber 32 via the first accumulator 26, and then to the second expansion chamber 34 via the second accumulator 28. As a result, the first expansion chamber 32 and the second expansion chamber 34 are pressurized from low pressure to high pressure. At this time, the displacement assembly 18 moves from bottom dead center to top dead center, and the volume of the first expansion chamber 32 and the second expansion chamber 34 increases. If the high-pressure valve 40a is closed, the intake process ends.

[0067] During the exhaust process, by closing the high-pressure valve 40a and opening the low-pressure valve 40b, the high-pressure first expansion chamber 32 and second expansion chamber 34 are connected to the low-pressure working gas inlet of the compressor 12. Therefore, the working gas expands in the first expansion chamber 32 and second expansion chamber 34, resulting in the low-pressure working gas being discharged from the first expansion chamber 32 and second expansion chamber 34 through the first accumulator 26 and second accumulator 28 towards the chamber temperature 30. At this time, the displacement assembly 18 moves from top dead center to bottom dead center, and the volume of the first expansion chamber 32 and second expansion chamber 34 decreases. The working gas is recovered from the expander 14 to the compressor 12 after passing through the low-pressure valve 40b. If the low-pressure valve 40b is closed, the exhaust process ends.

[0068] This forms a refrigeration cycle (e.g., a GM cycle), whereby the first cooling stage 33 and the second cooling stage 35 are cooled to the desired ultra-low temperature. The first cooling stage 33 can be cooled to a first cooling temperature (e.g., in the range of about 20K to about 40K). The second cooling stage 35 can be cooled to a second cooling temperature lower than the first cooling temperature (e.g., about 1K to about 4K).

[0069] The cryogenic refrigerator 10 is capable of performing initial cooling and steady-state operation following initial cooling. Initial cooling is the operating mode of the expander 14, which rapidly cools from an initial temperature to a cryogenic temperature when the cryogenic refrigerator 10 is started. Steady-state operation is the operating mode of the expander 14, which maintains the cryogenic state achieved through initial cooling. The initial temperature can be the ambient temperature (e.g., room temperature). Furthermore, initial cooling can also be performed when restarting a cryogenic device (e.g., a superconducting device such as an MRI system) equipped with the cryogenic refrigerator 10 after maintenance. During maintenance, the cooled material inside the cryogenic device may sometimes remain at a low temperature (e.g., 20–80 K) instead of rising to the ambient temperature. In this case, the initial temperature can be the aforementioned low temperature.

[0070] The expander 14 is cooled to a standard cooling temperature based on initial cooling and maintained within the permissible temperature range of cryogenicity, including this standard cooling temperature, during steady-state operation. The standard cooling temperature varies depending on the application and settings of the cryogenic refrigerator 10. For example, in cooling applications for superconducting devices, a typical standard cooling temperature is below approximately 4.2 K. In other cooling applications, the standard cooling temperature may be, for example, between approximately 10 K and 20 K, or below 10 K. As mentioned above, initial cooling can also be referred to as temperature reduction.

[0071] However, during initial cooling, as the temperature drops from the initial temperature to the cryogenic temperature, the density of the working gas within the expander 14 increases. Consequently, the amount of working gas stored within the expander 14 increases, meaning that working gas is drawn into the expander 14 from the gas line 62. As a result, as the expander 14 cools, the pressure of the working gas circulating within the gas line 62 gradually decreases. This pressure drop in the working gas leads to a reduction in the cooling capacity of the cryogenic refrigerator 10, and therefore may contribute to a longer initial cooling time. Initial cooling is merely a preparation for beginning the cooling of the object using the cryogenic refrigerator; therefore, it is desirable that the required time be as short as possible.

[0072] To address this issue, in this embodiment, the controller 110 controls the supply valve 72 during the initial cooling period based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, so that the pressure of the high-pressure line 63 is maintained within a preset appropriate pressure range. More specifically, the controller 110 may compare the measured pressure of the high-pressure line 63 during the initial cooling period with a lower limit Pc of the appropriate pressure range and actuate the supply valve 72 to repeatedly open and close it, so as to prevent the pressure of the high-pressure line 63 from falling below the lower limit Pc.

[0073] Furthermore, in this embodiment, the controller 110 controls the recovery valve 74 during the initial cooling period based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, so as to maintain the pressure of the high-pressure line 63 within an appropriate pressure range. More specifically, the controller 110 may compare the measured pressure of the high-pressure line 63 during the initial cooling period with an upper limit value Pd of the appropriate pressure range and actuate the recovery valve 74 to repeatedly open and close it, so as to prevent the pressure of the high-pressure line 63 from exceeding the upper limit value Pd.

[0074] Figure 3 This is a flowchart illustrating the control method of the cryogenic refrigerator 10 according to the first embodiment. During the initial cooling of the cryogenic refrigerator 10, the controller 110 repeatedly executes this method according to a predetermined cycle. Furthermore, this method can be executed not only during the initial cooling period but also during the steady-state operation of the cryogenic refrigerator 10.

[0075] First, the pressure of the high-pressure line 63 is measured (S10). The first pressure sensor 54 measures the pressure of the high-pressure line 63 and outputs a first measured pressure signal PH representing the measured pressure of the high-pressure line 63. The controller 110 receives the first measured pressure signal PH to obtain the measured pressure of the high-pressure line 63.

[0076] Next, the measured pressure of the high-pressure line 63 is compared with an appropriate pressure range (S12). The lower limit Pc of the appropriate pressure range is set to ensure that the cryogenic refrigerator 10 provides sufficient cooling capacity. The upper limit Pd of the appropriate pressure range is set to prevent excessive pressure from being generated in the high-pressure line 63. The upper limit Pd of the appropriate pressure range can be set to a pressure value lower than the aforementioned set pressure that opens the safety valve 60. The appropriate pressure range can be appropriately set based on the designer's experience, experiments, or simulations. The appropriate pressure range can be pre-stored in the controller 110 as the initial setting for the cryogenic refrigerator 10, or it can be set by the user in the controller 110 before the cryogenic refrigerator 10 is operated.

[0077] As an example, the upper limit Pd and lower limit Pc of the appropriate pressure range can be selected from the range of 2 MPa to 3 MPa or the range of 2.1 MPa to 2.7 MPa. The range of the appropriate pressure range (i.e., the difference between the upper limit Pd and the lower limit Pc) can be set to a value within 0.5 MPa, 0.3 MPa, or 0.1 MPa. For example, the appropriate pressure range can be set to 2.45 ± 0.05 MPa, in which case the range of the appropriate pressure range is 0.1 MPa, the upper limit Pd is 2.5 MPa, and the lower limit Pc is 2.4 MPa.

[0078] The controller 110 compares the measured pressure of the high-pressure line 63 with the lower limit Pc of the appropriate pressure range, and opens the supply valve 72 (S14) when the measured pressure of the high-pressure line 63 is lower than the lower limit Pc (PH < Pc). As a result, working gas is supplied from the buffer volume 70 to the low-pressure line 64 after passing through the supply valve 72. Because the amount of working gas circulating in the gas line 62 increases, the pressure in the high-pressure line 63 is restored.

[0079] The controller 110 closes the supply valve 72 (S16) when the measured pressure of the high-pressure line 63 returns to the appropriate pressure range. For example, the controller 110 can compare the measured pressure of the high-pressure line 63 with the lower limit Pc of the appropriate pressure range, and close the supply valve 72 when the measured pressure of the high-pressure line 63 becomes above the lower limit Pc (PH>Pc or PH≥Pc). If the supply valve 72 is closed, the supply of working gas from the buffer volume 70 to the low-pressure line 64 is stopped. Thus, the method ends and is executed again in the next control cycle.

[0080] Furthermore, the pressure threshold for closing the supply valve 72 may differ from the lower limit Pc of the appropriate pressure range; for example, it may be greater than the lower limit Pc. This pressure threshold may be set to not exceed the upper limit Pd of the appropriate pressure range. For example, the pressure threshold may also be a value obtained by adding a predetermined proportion of the range of the appropriate pressure range (upper limit Pd - lower limit Pc) to the lower limit Pc. The predetermined proportion may be, for example, less than 50%, less than 30%, or less than 10%.

[0081] Figure 4 This is a flowchart illustrating the control method of the cryogenic refrigerator 10 according to the first embodiment. During the initial cooling of the cryogenic refrigerator 10, the controller 110 repeatedly executes this method according to a predetermined cycle. This method can be combined with... Figure 3 The methods shown are executed together. In addition, this method can be executed not only during the initial cooling period, but also during the steady-state operation of the cryogenic refrigerator 10.

[0082] First, the pressure of the high-pressure line 63 is measured using the first pressure sensor 54 (S20). The controller 110 receives the first measured pressure signal PH from the first pressure sensor 54 to obtain the measured pressure of the high-pressure line 63.

[0083] Next, the measured pressure of the high-pressure line 63 is compared with an appropriate pressure range (S22). The controller 110 compares the measured pressure of the high-pressure line 63 with the upper limit Pd of the appropriate pressure range, and when the measured pressure of the high-pressure line 63 is greater than the upper limit Pd (PH > Pd), the recovery valve 74 is opened (S24). As a result, the working gas is recovered from the high-pressure line 63 to the buffer volume 70 after passing through the recovery valve 74, and the pressure of the high-pressure line 63 decreases.

[0084] When the measured pressure in the high-pressure line 63 returns to within the appropriate pressure range, the controller 110 closes the recovery valve 74 (S26). For example, the controller 110 can compare the measured pressure in the high-pressure line 63 with the upper limit Pd of the appropriate pressure range, and close the recovery valve 74 when the measured pressure in the high-pressure line 63 falls below the upper limit Pd (PH < Pd or PH ≤ Pd). Closing the recovery valve 74 stops the recovery of working gas from the high-pressure line 63 to the buffer volume 70. This terminates the process and allows it to be repeated in the next control cycle.

[0085] Furthermore, the pressure threshold for closing the recovery valve 74 can differ from the upper limit Pd of the appropriate pressure range; for example, it can be less than the upper limit Pd. This pressure threshold can be selected from the appropriate pressure range, i.e., it can be greater than the lower limit Pc of the appropriate pressure range.

[0086] During the operation of the cryogenic refrigerator 10, the appropriate pressure range can be varied. For example, the appropriate pressure range during initial cooling can differ from the appropriate pressure range during steady-state operation; for instance, it can be higher than the appropriate pressure range during steady-state operation. For example, the lower limit Pc during initial cooling can be higher than the lower limit Pc during steady-state operation, and / or, the upper limit Pd during initial cooling can be higher than the upper limit Pd during steady-state operation.

[0087] At this time, the switching from initial cooling to steady-state operation and the change of the appropriate pressure range can be controlled by the control device 100. For example, the control device 100 can compare the measured temperature of the second cooling stage 35 (and / or the first cooling stage 33) with the aforementioned standard cooling temperature based on the measured temperature signal from the temperature sensor 46, and perform initial cooling when the measured temperature is higher than the standard cooling temperature, and switch the initial cooling to steady-state operation when the measured temperature is lower than the standard cooling temperature. The controller 110 can also change the appropriate pressure range along with the switching from initial cooling to steady-state operation.

[0088] Furthermore, as referenced Figure 7 and Figure 8As will be explained later, the switching from initial cooling to steady-state operation and the change of appropriate pressure range can also be based on the pressure of the buffer volume 70 or the pressure difference between the high-pressure line 63 and the low-pressure line 64. In this way, the control device 100 can complete the initial cooling of the cryogenic refrigerator 10 without relying on the temperature sensor 46.

[0089] Here, in order to reliably supply the working gas from the buffer volume 70, the conditions required for the buffer volume 70 are considered. According to the ideal gas law, during the period when the cryogenic refrigerator 10 is not operating (i.e., before initial cooling), the following equation holds.

[0090] PI(VH+VL+VB)=nRT(1)

[0091] Here, PI (MPa) represents the working gas sealing pressure of the cryogenic refrigerator 10 at temperature T (K), VH (L) represents the volume of the high-pressure pipeline 63, VL (L) represents the volume of the low-pressure pipeline 64, VB (L) represents the volume of the buffer volume 70, n (mol) represents the amount of working gas in the cryogenic refrigerator 10, and R represents the gas constant.

[0092] Similarly, during the steady-state operation of the cryogenic refrigerator 10, the following equation holds true.

[0093] PHVH+PLVL+PBVB=nRT(2)

[0094] Here, PH (MPa) represents the pressure of high-pressure pipeline 63 in steady-state operation at temperature T, PL (MPa) represents the pressure of low-pressure pipeline 64 in steady-state operation at temperature T, and PB (MPa) represents the pressure of buffer volume 70 in steady-state operation at temperature T.

[0095] According to equations (1) and (2), we can obtain PI(VH+VL+VB)=PHVH+PLVL+PBVB(3).

[0096] In order to supply working gas from buffer volume 70 to low-pressure pipeline 64 at any time during the operation of cryogenic refrigerator 10, the following formula should be satisfied at any temperature T within the temperature range from the initial temperature to the cryogenic temperature of cryogenic refrigerator 10.

[0097] PL≤PB(4).

[0098] If we solve equation (3) to obtain PB and substitute it into equation (4), we can obtain the following relationship.

[0099] VB≥VH(PH-PI) / (PI-PL)-VL(5)

[0100] Therefore, in order to reliably supply working gas from buffer volume 70 to low-pressure line 64, it is preferable that buffer volume 70 satisfies equation (5) at any temperature in the temperature range from initial temperature to ultra-low temperature.

[0101] Similarly, in order to reliably recover gas from the buffer volume 70, the conditions that the buffer volume 70 needs to meet must be considered. At this time, in order to supply working gas from the buffer volume 70 to the high-pressure pipeline 63 at any time during the operation of the cryogenic refrigerator 10, the following formula should be satisfied at any temperature T within the temperature range from the initial temperature to the cryogenic temperature of the cryogenic refrigerator 10.

[0102] PB≤PH(6)

[0103] If we solve equation (3) to obtain PB and substitute it into equation (6), we can obtain the following relationship.

[0104] VB≥-VH+VL(PI-PL) / (PH-PI)(7)

[0105] Therefore, in order to reliably recover working gas from high-pressure pipeline 63 to buffer volume 70, it is preferable that buffer volume 70 satisfies equation (7) at any temperature in the temperature range from the initial temperature to the ultra-low temperature.

[0106] Figure 5 This is a graph illustrating an example of the time-varying temperature and pressure changes during operation of the cryogenic refrigerator 10 of the first embodiment. The pressure changes shown were obtained experimentally. Figure 5 The upper part shows the pressure PH of the high-pressure line 63 measured by the first pressure sensor 54 and the pressure PL of the low-pressure line 64 measured by the second pressure sensor 55. Figure 5 The lower part shows the temperature T1 of the first cooling stage 33 and the temperature T2 of the second cooling stage 35. The horizontal axis represents time.

[0107] Before starting the cryogenic refrigerator 10 (time 0), the pressure PH of the high-pressure line 63 and the pressure PL of the low-pressure line 64 are both the sealing pressure PI, and the temperatures T1 of the first cooling platform 33 and T2 of the second cooling platform 35 are both room temperature (approximately 300K). If the cryogenic refrigerator 10 is started to begin initial cooling, the compressor 12 and expander 14 begin operation. The pressure PH of the high-pressure line 63 increases from the sealing pressure PI, and the pressure PL of the low-pressure line 64 decreases from the sealing pressure PI. Through initial cooling, the temperatures T1 of the first cooling platform 33 and T2 of the second cooling platform 35 continuously decrease. If the first cooling platform 33 and the second cooling platform 35 are cooled to the aforementioned standard cooling temperatures (e.g., T1 ≤ 30K, T2 ≤ 4K), the initial cooling ends and the system switches to steady-state operation.

[0108] Figure 6 The enlarged representation in (A) shows Figure 5 Part A shown, Figure 6 The middle (B) section enlarges the representation of Figure 5 Part B is shown. Figure 6 In diagram (A), the pressure PH of the high-pressure line 63 after initial cooling is shown along with the opening and closing state of the recovery valve 74. Figure 6 In section (B), the pressure PH of the high-pressure line 63, which is further delayed than that in section A, is shown along with the opening and closing state of the supply valve 72.

[0109] like Figure 6 As shown in (A), if the pressure PH of the high-pressure line 63 exceeds the upper limit Pd of the appropriate pressure range, the recovery valve 74 is opened. The working gas is recovered from the high-pressure line 63 to the buffer volume 70 after passing through the recovery valve 74, thus reducing the pressure in the high-pressure line 63. If the pressure PH of the high-pressure line 63 becomes lower than the upper limit pressure Pd, the recovery valve 74 is closed. This prevents excessive pressure build-up in the high-pressure line 63. The risk of an emergency shutdown of the compressor 12 due to excessive pressure build-up is reduced. Furthermore, the buffer volume 70 is pressurized through the recovery of the working gas, thus it can be effectively used to supply working gas from the buffer volume 70 to the low-pressure line 64.

[0110] like Figure 6 As shown in (B), if the pressure PH of the high-pressure line 63 falls below the lower limit Pc of the appropriate pressure range, the supply valve 72 is opened. Working gas is supplied from the buffer volume 70 to the low-pressure line 64 through the supply valve 72. As the amount of working gas circulating in the gas line 62 increases, the pressure in the high-pressure line 63 is restored. If the pressure PH of the high-pressure line 63 exceeds the lower limit Pc, the supply valve 72 is closed.

[0111] As described above, due to the temperature drop in the expander 14 during initial cooling, the density of the working gas inside the expander 14 increases, which causes the pressure PH in the high-pressure line 63 to decrease. Therefore, even if the pressure PH in the high-pressure line 63 temporarily recovers, it will again fall below the lower limit value Pc. At this time, the supply valve 72 is opened again, and if the pressure in the high-pressure line 63 recovers, the supply valve 72 is closed. Thus, the supply valve 72 operates in a repeated opening and closing manner to maintain the pressure PH in the high-pressure line 63 within an appropriate pressure range.

[0112] Assuming that working gas is not supplied to gas line 62 during the initial cooling period, the pressure PH of high-pressure line 63 may decrease significantly due to the temperature drop in expander 14. The cooling capacity of cryogenic refrigerator 10 is related to the pressure PH of high-pressure line 63; therefore, the cooling capacity of cryogenic refrigerator 10 may decrease as initial cooling progresses. This would be a reason for the longer initial cooling time.

[0113] In contrast, according to the embodiment, by controlling the supply valve 72 during the initial cooling period, the pressure PH of the high-pressure line 63 can be maintained within an appropriate pressure range. Therefore, the cooling capacity of the cryogenic refrigerator 10 can be reliably maintained, and the increase in initial cooling time can be suppressed. Furthermore, by keeping the pressure PH of the high-pressure line 63 substantially constant, the cryogenic refrigerator 10 can provide stable cooling capacity.

[0114] To maintain the pressure PH of the high-pressure line 63 within an appropriate pressure range, a method of controlling the supply valve 72 and the recovery valve 74 based on the pressure of the low-pressure line 64 can also be considered. The pressure of the low-pressure line 64 is affected by the cooling temperature of the expander 14 (it varies depending on the cooling temperature). Therefore, in practical applications, the appropriate pressure range of the low-pressure line 64 (i.e., the pressure threshold of the low-pressure line 64 used to open and close the supply valve 72 and the recovery valve 74) must be set to a value that varies depending on the cooling temperature, thus complicating the control design. Furthermore, even if the low-pressure line 64 is within an appropriate pressure range, the pressure of the high-pressure line 63 may become excessively high depending on the cooling temperature. Therefore, a method based on the pressure of the high-pressure line 63, as in the embodiment, is advantageous in mitigating or preventing such adverse conditions.

[0115] Figure 7 This is a graph showing an example of the time-varying temperature and pressure changes during the operation of the cryogenic refrigerator 10 of the first embodiment. Figure 8 This is a diagram that schematically illustrates the cryogenic refrigerator 10 according to the first embodiment.

[0116] Similar to the embodiments described above, the cryogenic refrigerator 10 includes a compressor 12, an expander 14, a buffer volume 70, and a control device 100. During initial cooling, the controller 110 controls the supply valve 72 based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, thereby maintaining the pressure of the high-pressure line 63 within a preset appropriate pressure range. Furthermore, during initial cooling, the controller 110 controls the recovery valve 74 based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, thereby maintaining the pressure of the high-pressure line 63 within an appropriate pressure range.

[0117] The cryogenic refrigerator 10 includes a buffer pressure sensor 76 connected to a buffer volume 70 to measure the pressure of the buffer volume 70. The buffer pressure sensor 76 is configured to be electrically connected to the control device 100 and output a measured buffer pressure signal PB, representing the measured pressure, to the control device 100.

[0118] exist Figure 7 The upper part shows Figure 5The pressure PH of the high-pressure line 63 and the pressure PL of the low-pressure line 64 are shown, and the pressure PB of the buffer volume 70 measured by the buffer pressure sensor 76 is also shown. Figure 7 The lower part shows the temperature T1 of the first cooling platform 33 and the temperature T2 of the second cooling platform 35. From Figure 7 It can be seen that if the cryogenic refrigerator 10 is sufficiently cooled after the initial cooling is completed and the temperatures of the first cooling platform 33 and the second cooling platform 35 become stable, then the pressure PH of the high-pressure pipeline 63 and the pressure PL of the low-pressure pipeline 64 will also become stable. At this time, both the supply valve 72 and the recovery valve 74 are closed, and the buffer volume 70 is disconnected from the gas pipeline 62. Therefore, the pressure PB of the buffer volume 70 will also become constant. Figure 7 The final buffer pressure PF is shown.

[0119] Therefore, by detecting when the pressure PB of buffer volume 70 stabilizes, the end of the initial cooling can be determined. If the working gas inlet pressure PI and operating conditions of the cryogenic refrigerator 10 are known (e.g., high pressure PH, low pressure PL, temperature T1, T2, etc.), the final pressure of buffer volume 70 at the end of the initial cooling can be predicted. At this time, the controller 110 can also compare the predicted final buffer pressure with the measured pressure PB of buffer volume 70, and determine whether the measured pressure PB of buffer volume 70 is equal to the predicted final buffer pressure based on the comparison result. The controller 110 can also terminate the initial cooling if the state where the measured pressure PB of buffer volume 70 is equal to the predicted final buffer pressure continues for a predetermined time (e.g., several minutes).

[0120] Alternatively, controller 110 can calculate the difference between the measured pressure PB of buffer volume 70 and the reference pressure during the initial cooling period and determine the end of the initial cooling period by detecting when the calculated pressure difference stabilizes. The reference pressure can be the previously measured pressure of buffer volume 70, for example, it can be the maximum pressure PM of buffer volume 70 measured during the initial cooling period. Figure 7 It can be seen that the pressure of the buffer volume 70 increases from the initial sealing pressure PI after the initial cooling and reaches the maximum value PM.

[0121] The controller 110 can compare the calculated pressure difference (i.e., the difference between the measured pressure PB of the buffer volume 70 and the reference pressure) with the target pressure difference value and determine whether the calculated pressure difference is equal to the target pressure difference value based on the comparison result. The controller 110 can end the initial cooling when the state in which the calculated pressure difference is equal to the target pressure difference value continues for a specified time. The specified time can be selected, for example, from more than 1 minute to less than 10 minutes. If the difference between the calculated pressure difference and the target pressure difference value is within a specified value (e.g., 0.05 MPa), the calculated pressure difference can be considered equal to the target pressure difference value. This target pressure difference value does not depend on the sealing pressure PI, therefore, even if the sealing pressure PI is unknown, the end of the initial cooling can be determined.

[0122] As another example of reference pressure, the pressure PH of the high-pressure line 63 (or the pressure PL of the low-pressure line 64) measured simultaneously with the measured pressure PB of the buffer volume 70 can also be used. The controller 110 can also calculate the difference between the measured pressure PB of the buffer volume 70 and the measured pressure PH of the high-pressure line 63 (or the measured pressure PL of the low-pressure line 64) and detect when the calculated pressure difference becomes stable to determine the end of the initial cooling. Similarly, as in the example above, the controller 110 can compare the calculated pressure difference with a target pressure difference value and end the initial cooling when the calculated pressure difference equals the target pressure difference value and remains so for a specified time.

[0123] As a further alternative, the controller 110 can also calculate the difference between the measured pressure PH of the high-pressure line 63 and the measured pressure PL of the low-pressure line 64, and detect when the calculated pressure difference becomes stable to determine the end of the initial cooling.

[0124] In the above embodiment, during the initial cooling period, the supply valve 72 (hereinafter also referred to as high-pressure priority control) is controlled based on the measured pressure of the high-pressure line 63, thereby maintaining the pressure of the high-pressure line 63 within an appropriate pressure range. At this time, since the pressure of the low-pressure line 64 is not managed, it is possible that the pressure of the low-pressure line 64 may become too low, which is undesirable.

[0125] To address this problem, the controller 110 can be configured such that when the pressure of the low-pressure line 64, as measured by the second pressure sensor 55, falls below a preset low-pressure threshold, the control of the supply valve 72 based on the pressure of the high-pressure line 63 is interrupted (i.e., high-pressure priority control). The controller 110 can also be configured to control the supply valve 72 based on the pressure of the low-pressure line 64 measured by the second pressure sensor 55, so that the pressure of the low-pressure line 64 returns to the low-pressure threshold. Hereinafter, the control of the supply valve 72 based on the pressure of the low-pressure line 64 will also be referred to as low-pressure priority control. An example of such a switching process from high-pressure priority control to low-pressure priority control will be referred to later. Figure 9 Please provide an explanation.

[0126] Figure 9 This is a flowchart illustrating the control method of the cryogenic refrigerator 10 according to the first embodiment. During the initial cooling of the cryogenic refrigerator 10, the controller 110 repeatedly executes this method according to a predetermined cycle. Furthermore, this method can be executed not only during the initial cooling period but also during the steady-state operation of the cryogenic refrigerator 10.

[0127] First, the pressure of the low-pressure line 64 is measured (S30). The second pressure sensor 55 measures the pressure of the low-pressure line 64 and outputs a second measured pressure signal PL representing the measured pressure of the low-pressure line 64. The controller 110 receives the second measured pressure signal PL to obtain the measured pressure of the low-pressure line 64.

[0128] Next, the measured pressure PL of the low-pressure line 64 is compared with the low-pressure threshold Pe (S32). For example, from the viewpoint of ensuring stable operation of the compressor 12, the low-pressure threshold Pe can be set as the lower limit of the pressure of the low-pressure line 64. For example, the low-pressure threshold Pe can be selected from the range of 0.2 MPa to 0.4 MPa. The low-pressure threshold Pe can be appropriately set according to the designer's experience or the designer's experiments or simulations. The low-pressure threshold Pe can be stored in the controller 110 as the initial setting of the cryogenic refrigerator 10, or it can be set by the user in the controller 110 before the cryogenic refrigerator 10 is operated.

[0129] The controller 110 compares the measured pressure of the low-pressure line 64 with the low-pressure threshold Pe, and selects high-pressure priority control when the measured pressure of the low-pressure line 64 is above the low-pressure threshold Pe (PL>Pe or PL≥Pe). At this time, as referenced... Figure 3As explained, controller 110 compares the measured pressure of high-pressure line 63 with the lower limit Pc of the appropriate pressure range and actuates supply valve 72 to repeatedly open and close it to prevent the pressure of high-pressure line 63 from falling below the lower limit Pc. This continuously executes high-pressure priority control.

[0130] On the other hand, when the measured pressure in low-pressure line 64 is lower than the low-pressure threshold Pe (PL < Pe), controller 110 selects low-pressure priority control (S36). High-pressure priority control is interrupted and low-pressure priority control begins. An example of low-pressure priority control will be referred to later. Figure 10 This will be explained. Thus, the switching process from high-voltage priority control to low-voltage priority control is complete.

[0131] like Figure 10 As shown, in low-pressure priority control, the pressure of low-pressure line 64 is first measured (S40). Next, the measured pressure of low-pressure line 64 is compared with the low-pressure threshold Pe (S42). When the measured pressure of low-pressure line 64 is lower than the low-pressure threshold Pe (PL < Pe), controller 110 opens supply valve 72 (S44). As a result, working gas is supplied from buffer volume 70 through supply valve 72 to low-pressure line 64, restoring the pressure in low-pressure line 64.

[0132] On the other hand, when the measured pressure in the low-pressure line 64 is above the low-pressure threshold Pe (PL > Pe or PL ≥ Pe), the controller 110 closes the supply valve 72 (S46). The supply of working gas from the buffer volume 70 to the low-pressure line 64 is stopped. Furthermore, the pressure threshold for closing the supply valve 72 may be different from the low-pressure threshold Pe; for example, it may be slightly higher than the low-pressure threshold Pe. Thus, this method ends and is executed again in the next control cycle.

[0133] According to the low-pressure priority control described above, the supply valve 72 can be opened and closed based on the pressure of the low-pressure line 64, and the pressure of the low-pressure line 64 can be restored to the low-pressure threshold Pe. However, in the low-pressure priority control, the pressure of the high-pressure line 63 is not managed. Therefore, during the low-pressure priority control, the undesirable phenomenon of the pressure of the high-pressure line 63 becoming too low may occur.

[0134] Therefore, the controller 110 can be configured such that when the pressure of the high-pressure line 63, as measured by the first pressure sensor 54, is lower than the high-pressure threshold, the control of the supply valve 72 based on the pressure of the low-pressure line 64 is interrupted. The controller 110 can also be configured such that the supply valve 72 is controlled based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, so that the pressure of the high-pressure line 63 is restored to the high-pressure threshold. An example of such a recovery process from low-pressure priority control to high-pressure priority control will be referred to later. Figure 11 Please provide an explanation.

[0135] Figure 11 This is a flowchart illustrating the control method of the cryogenic refrigerator 10 according to the first embodiment. In the execution of the low-pressure priority control described above, the controller 110 repeatedly executes this method according to a predetermined cycle.

[0136] First, the pressure in the high-pressure line 63 is measured (S50). Next, the measured pressure in the high-pressure line 63 is compared with a high-pressure threshold Pf (S52). The high-pressure threshold Pf can be, for example, the lower limit Pc of an appropriate pressure range. The high-pressure threshold Pf can be appropriately set based on the designer's experience, experiments, or simulations. The high-pressure threshold Pf can be pre-stored in the controller 110 as an initial setting for the cryogenic refrigerator 10, or it can be set by the user in the controller 110 before the cryogenic refrigerator 10 is operated.

[0137] The controller 110 compares the measured pressure of the high-pressure line 63 with the high-pressure threshold Pf, and selects low-pressure priority control when the measured pressure of the high-pressure line 63 is above the high-pressure threshold Pf (PH>Pf or PH≥Pf). At this time, low-pressure priority control continues to be executed.

[0138] On the other hand, when the measured pressure of the high-pressure line 63 is lower than the high-pressure threshold Pf (PH < Pf), the controller 110 selects high-pressure priority control (S56). Thus, the switching process from low-pressure priority control to high-pressure priority control ends. By switching back to high-pressure priority control, the supply valve 72 is controlled according to the measured pressure of the high-pressure line 63, and the pressure of the high-pressure line 63 is maintained within an appropriate pressure range.

[0139] However, the operating pressure difference of the cryogenic refrigerator 10 (the pressure difference between the high-pressure line 63 and the low-pressure line 64) can also be increased, thereby increasing the cooling capacity of the cryogenic refrigerator 10 and shortening the initial cooling time. However, in the above embodiment, the safety valve 60, which bypasses the high-pressure line 63 and the low-pressure line 64, may become an obstacle. When the safety valve 60 is of the type that mechanically opens when a pressure difference exceeding the set pressure acts between its inlet and outlet, the operating pressure difference of the cryogenic refrigerator 10 will be limited by the set pressure. This is because if the pressure difference between the high-pressure line 63 and the low-pressure line 64 exceeds the set pressure of the safety valve 60, the safety valve 60 will mechanically open, and the working gas will flow from the high-pressure line 63 through the safety valve 60 to the low-pressure line 64. As a result, the increase in the operating pressure difference of the cryogenic refrigerator 10 will be hindered.

[0140] To address this issue, as explained below, a compressor can be temporarily added to the cryogenic refrigerator 10 for initial cooling. For ease of explanation, the main compressor 12 of the cryogenic refrigerator 10 will be referred to as the first compressor 12, and the added auxiliary compressor will be referred to as the second compressor 80.

[0141] Figure 12 and Figure 13 This is a diagram that schematically illustrates the cryogenic refrigerator 10 according to the second embodiment. Figure 12 The diagram shows the setup of the cryogenic refrigerator 10 during initial cooling. Figure 13 The basic setup of the cryogenic refrigerator 10 in steady-state operation before or after initial cooling is shown. Figure 14 This is a flowchart illustrating the operation method of the cryogenic refrigerator 10 according to the second embodiment.

[0142] Except for the second compressor 80, the cryogenic refrigerator 10 and its operating method according to the second embodiment can be the same as those according to the cryogenic refrigerator 10 and its operating method according to the first embodiment. Therefore, in Figure 12 and Figure 13 In this document, structures identical to those in the first embodiment are marked with the same reference numerals and their detailed descriptions are omitted as appropriate to avoid redundancy.

[0143] like Figure 13 As shown, the cryogenic refrigerator 10 is in a basic configuration with a first compressor 12 and an expander 14 before initial cooling. The first compressor 12 and the expander 14 are connected via a high-pressure line 63 and a low-pressure line 64. The second compressor 80 and the buffer volume 70 are not connected to the cryogenic refrigerator 10.

[0144] In the operation method of the cryogenic refrigerator 10 according to the second embodiment, such as Figure 14 As shown, as a pretreatment for initial cooling, the second compressor 80 and the buffer volume 70 are connected to the cryogenic refrigerator 10 (S60, S61). The installation order of the second compressor 80 and the buffer volume 70 is irrelevant.

[0145] The second compressor 80 is installed on the high-pressure line 63 and connected in series with the first compressor 12. More specifically, as... Figure 12 As shown, the high-pressure gas outlet 50 of the first compressor 12 is connected to the suction port of the second compressor 80, and the discharge port of the second compressor 80 is connected to the high-pressure gas inlet 22 of the expander 14. Therefore, the cryogenic refrigerator 10 has a two-stage compressor structure consisting of the first compressor 12 and the second compressor 80.

[0146] The buffer volume 70 is connected to the low-pressure line 64 via the supply valve 72 and to the high-pressure line 63 via the recovery valve 74. The supply valve 72 and the recovery valve 74 can be housed together with the buffer volume 70 in a single frame to form a buffer volume unit. The buffer volume unit and the second compressor 80 can be brought into the operating site of the cryogenic refrigerator 10 by maintenance personnel and connected to the cryogenic refrigerator 10.

[0147] After connecting the second compressor 80 and the buffer volume 70 to the cryogenic refrigerator 10, the cryogenic refrigerator 10 is started to begin initial cooling (S62). As described above, initial cooling is a process of cooling the cryogenic refrigerator 10 from an initial temperature to a target cryogenic temperature as preparation for steady-state operation. The initial temperature can be the ambient temperature (e.g., room temperature), or it can be a temperature lower than the ambient temperature but higher than the target cryogenic temperature (e.g., a temperature selected from the range of 20K to 80K). Through initial cooling, the first cooling stage 33 of the expander 14 is cooled to a first cooling temperature, and the second cooling stage 35 is cooled to a second cooling temperature.

[0148] With the second compressor 80 and buffer volume 70 connected to the cryogenic refrigerator 10, initial cooling is performed. Therefore, during initial cooling, the first compressor 12 and the second compressor 80 supply working gas to the expander 14. The first compressor 12 pressurizes the working gas from the expander 14, recovered through the low-pressure line 64, and supplies the pressurized working gas to the second compressor 80. The second compressor 80 further pressurizes the working gas from the first compressor 12 and supplies it back to the expander 14.

[0149] Furthermore, during initial cooling, similar to the first embodiment, the buffer volume 70 is used to maintain the pressure of the high-pressure line 63 within an appropriate pressure range. That is, during initial cooling, the supply valve 72 is controlled based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54 to maintain the pressure of the high-pressure line 63 within an appropriate pressure range.

[0150] If the initial cooling is complete, remove the second compressor 80 and buffer volume 70 (S63, S64) from the cryogenic refrigerator 10. The order in which the second compressor 80 and buffer volume 70 are removed is irrelevant. The cryogenic refrigerator 10 is then returned to its original position. Figure 13 The basic settings are shown. Then, steady-state operation of the cryogenic refrigerator 10 is performed (S65).

[0151] According to the second embodiment, by adding a second compressor 80, the operating pressure differential of the cryogenic refrigerator 10 can be increased. In particular, the limitation caused by the set pressure of the safety valve 60 of the first compressor 12 can be overcome, thereby increasing the operating pressure differential of the cryogenic refrigerator 10. The increase in operating pressure differential will increase the cooling capacity of the cryogenic refrigerator 10, thereby shortening the initial cooling time.

[0152] As another method to increase the operating pressure differential of the cryogenic refrigerator 10, it is also possible to bring a large compressor with a power greater than that of the first compressor 12 from outside to the site and replace it with the first compressor 12. However, such a large compressor is usually large in size and weight, and therefore unsuitable for transportation. In contrast, since the second compressor 80 is used in conjunction with the first compressor 12, the second compressor 80 can be small and easy to transport.

[0153] In the above embodiment, to create a two-stage compressor structure, the second compressor 80 is connected to the discharge side (outlet side) of the first compressor 12. However, other structures can also be used. For example, in principle, the second compressor 80 can also be connected to the suction side (inlet side) of the first compressor 12. That is, the second compressor 80 can be installed on the low-pressure line 64 and connected in series with the first compressor 12.

[0154] Furthermore, disassembling the buffer volume 70 is not necessarily required. In the second embodiment, similarly to the first embodiment, as... Figure 1 As shown, the cryogenic refrigerator 10 can be operated in steady state with the buffer volume 70 connected to it. Alternatively, in the first embodiment, similar to the second embodiment, the buffer volume 70 can be removed from the cryogenic refrigerator 10 after initial cooling.

[0155] Figure 15 This is a diagram that schematically illustrates the cryogenic refrigerator 10 according to the third embodiment. Figure 16 and Figure 17 This is a flowchart illustrating the operation method of the cryogenic refrigerator 10 according to the third embodiment.

[0156] Except for the second compressor 80, the cryogenic refrigerator 10 and its operating method according to the third embodiment can be the same as those according to the cryogenic refrigerator 10 and its operating method according to the first embodiment. Therefore, in Figure 15 In this document, structures identical to those in the first embodiment are marked with the same reference numerals and their detailed descriptions are omitted as appropriate to avoid redundancy.

[0157] like Figure 13As shown, in the third embodiment, similarly to the second embodiment, the cryogenic refrigerator 10 is in a basic configuration with a first compressor 12 and an expander 14 before initial cooling. The first compressor 12 and the expander 14 are connected via a high-pressure line 63 and a low-pressure line 64. The second compressor 80 is not connected to the cryogenic refrigerator 10.

[0158] In the operation method of the cryogenic refrigerator 10 according to the third embodiment, such as Figure 16 As shown, as a pretreatment for initial cooling, the second compressor 80 is connected to the cryogenic refrigerator 10 (S70). The second compressor 80 is installed on the high-pressure line 63 and connected in series with the first compressor 12. Figure 15 As shown, the high-pressure gas outlet 50 of the first compressor 12 is connected to the suction inlet of the second compressor 80, and the discharge outlet of the second compressor 80 is connected to the high-pressure gas inlet 22 of the expander 14. Therefore, the cryogenic refrigerator 10 has a two-stage compressor structure consisting of the first compressor 12 and the second compressor 80. The second compressor 80 can be brought into the operating site of the cryogenic refrigerator 10 by maintenance personnel and connected to the cryogenic refrigerator 10.

[0159] Similar to the first compressor 12, the second compressor 80 includes a compressor body 57. Furthermore, the second compressor 80 includes a compressor motor 82 with a variable operating frequency (i.e., speed), which drives the compressor body 57. The compressor motor 82 can be, for example, an electric motor, or any other suitable type of motor. By increasing the operating frequency of the compressor motor 82, the discharge flow rate of the compressor body 57 increases, resulting in an increase in the pressure of the high-pressure line 63. Conversely, by decreasing the operating frequency of the compressor motor 82, the discharge flow rate of the compressor body 57 decreases, resulting in a decrease in the pressure of the high-pressure line 63.

[0160] The control device 100 includes a frequency converter 90 that controls the operating frequency of the compressor motor 82. The compressor motor 82 and the frequency converter 90 are powered by an external power source 92, such as a commercial power supply (three-phase AC power). As explained later, the frequency converter 90 is configured such that, under the control of the controller 110, it adjusts the frequency of the power input from the external power source 92 and outputs it to the compressor motor 82 at any frequency. The operating frequency of the compressor motor 82 corresponds to the output frequency of the frequency converter 90, and for example, it can be adjusted within the range of 30Hz to 100Hz or within the range of 40Hz to 70Hz.

[0161] With the second compressor 80 connected to the cryogenic refrigerator 10, the cryogenic refrigerator 10 is started for initial cooling (S72). Working gas is supplied to the expander 14 using the first compressor 12 and the second compressor 80. The first compressor 12 pressurizes the working gas recovered from the expander 14 through the low-pressure line 64 and supplies the pressurized working gas to the second compressor 80. The second compressor 80 further pressurizes the working gas from the first compressor 12 and supplies it back to the expander 14. As described below, the operating frequency of the compressor motor 82 of the second compressor 80 is controlled based on the measured pressure of the high-pressure line 63 to maintain the pressure of the high-pressure line 63 within an appropriate pressure range.

[0162] If the initial cooling is complete, the second compressor 80 is removed from the cryogenic refrigerator 10 (S73). The cryogenic refrigerator 10 is then returned to its original position. Figure 13 The basic settings are shown. Then, steady-state operation of the cryogenic refrigerator 10 is performed (S75).

[0163] refer to Figure 17 An example of the control processing for the operating frequency of the compressor motor 82 based on the measured pressure of the high-pressure line 63 will be described. During the initial cooling of the cryogenic refrigerator 10, the controller 110 repeatedly performs this process according to a predetermined cycle.

[0164] First, the pressure of the high-pressure line 63 is measured (S80). Next, the measured pressure of the high-pressure line 63 is compared with the high-pressure target value Pg (S82). The high-pressure target value Pg can, for example, be the lower limit Pc of an appropriate pressure range. The high-pressure target value Pg can be appropriately set based on the designer's experience, experiments, or simulations. The high-pressure target value Pg can be pre-stored in the controller 110 as the initial setting for the cryogenic refrigerator 10, or it can be set by the user in the controller 110 before the cryogenic refrigerator 10 is put into operation.

[0165] The controller 110 compares the measured pressure PH of the high-pressure pipeline 63 with the high-pressure target value Pg and outputs the relationship between the two as the comparison result. That is, the comparison result of the controller 110 represents one of the following three states: (i) the measured pressure PH is less than the high-pressure target value Pg, (ii) the measured pressure PH is greater than the high-pressure target value Pg, and (iii) the measured pressure PH is equal to the high-pressure target value Pg.

[0166] The inverter 90 is controlled based on the comparison result of the controller 110, and the operating frequency of the compressor motor 82 is controlled based on the output frequency of the inverter 90. Specifically, (i) when the measured pressure PH is less than the high-pressure target value Pg, the controller 110 controls the inverter 90 by increasing the operating frequency of the compressor motor 82 (S84). This increases the pressure in the high-pressure line 63. (ii) when the measured pressure PH is greater than the high-pressure target value Pg, the controller 110 controls the inverter 90 by decreasing the operating frequency of the compressor motor 82 (S18). This decreases the pressure in the high-pressure line 63. (iii) when the measured pressure PH is equal to the high-pressure target value Pg, there is no need to increase or decrease the operating frequency of the compressor motor 82; therefore, the controller 110 controls the inverter 90 by maintaining the current operating frequency. Alternatively, case (iii) can be included in either (i) or (ii).

[0167] When increasing or decreasing the operating frequency of the compressor motor 82, the controller 110 can increase or decrease the operating frequency by a predetermined amount from the current operating frequency value of the compressor motor 82. However, if the current operating frequency value has already reached the upper limit when the controller wants to increase the operating frequency, the controller 110 can maintain that upper limit value without increasing the operating frequency. For example, if the available range of the operating frequency of the compressor motor 82 is 30Hz to 100Hz and the current value is already the upper limit of 100Hz, the controller 110 will maintain the operating frequency at 100Hz and will not increase it further from 100Hz. Similarly, if the current operating frequency value has already reached the lower limit when the controller wants to decrease the operating frequency, the controller 110 can maintain that lower limit value without decreasing the operating frequency.

[0168] Alternatively, the controller 110 can control the inverter 90 to adjust the operating frequency of the compressor motor 82 to minimize the deviation between the measured pressure PH and the high-pressure target value Pg (e.g., through feedback control such as PID control). Thus, the controller 110 controls the inverter 90 as follows: it compares the pressure of the high-pressure line 63 with the target pressure, and decreases the operating frequency of the compressor motor 82 when the pressure of the high-pressure line 63 is greater than the target pressure, and increases the operating frequency of the compressor motor 82 when the pressure of the high-pressure line 63 is lower than the target pressure.

[0169] According to the third embodiment, by adding a second compressor 80, the operating pressure differential of the cryogenic refrigerator 10 can be increased. In particular, the limitation caused by the set pressure of the safety valve 60 of the first compressor 12 can be overcome, thereby increasing the operating pressure differential of the cryogenic refrigerator 10. The increase in operating pressure differential will increase the cooling capacity of the cryogenic refrigerator 10, thereby shortening the initial cooling time. Furthermore, since the second compressor 80 is used in conjunction with the first compressor 12, the second compressor 80 can be small and easy to transport.

[0170] Similarly to the second embodiment, in the third embodiment, as... Figure 18 As shown, the buffer volume 70 can also be connected to the cryogenic refrigerator 10 along with the supply valve 72 and the recovery valve 74 for initial cooling. As a pretreatment for initial cooling, the buffer volume 70 is connected to the low-pressure line 64 via the supply valve 72 and to the high-pressure line 63 via the recovery valve 74. During initial cooling, similar to the first embodiment, the buffer volume 70 is used to maintain the pressure of the high-pressure line 63 within an appropriate pressure range. That is, during initial cooling, the supply valve 72 is controlled based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54 to maintain the pressure of the high-pressure line 63 within an appropriate pressure range. After initial cooling, the buffer volume 70 can be removed from the cryogenic refrigerator 10 along with the supply valve 72 and the recovery valve 74. Therefore, by utilizing the buffer volume 70 during initial cooling, similar to the embodiment described above, the time required for initial cooling can be shortened.

[0171] And, as Figure 19 As shown, to form a two-stage compressor structure, the second compressor 80 can also be connected to the suction side (inlet side) of the first compressor 12. That is, the second compressor 80 can be installed on the low-pressure line 64 and connected in series with the first compressor 12. In this case, the operating frequency of the compressor motor 82 driving the compressor body 57 of the first compressor 12 can be variable. The operating frequency of the compressor motor 82 can be controlled by the controller 110 and the frequency converter 90 according to the measured pressure of the high-pressure line 63, so that the pressure of the high-pressure line 63 is maintained within an appropriate pressure range. Simultaneously or alternatively, with... Figure 15 Similarly, in the embodiment shown, the operating frequency of the compressor motor 82 of the second compressor 80 can also be controlled by the controller 110 and the frequency converter 90.

[0172] The present invention has been described above with reference to embodiments. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various design changes and modifications are possible, and such modifications are also within the scope of the present invention. Various features described in one embodiment can also be applied to another embodiment. New embodiments resulting from combinations possess the effects of each of the combined embodiments.

[0173] For example, the control processes described in the first embodiment (e.g., the termination process of initial cooling based on buffer pressure, the switching process from high-pressure priority control to low-pressure priority control, and the switching process from low-pressure priority control to high-pressure priority control) can also be applied to the second and third embodiments.

[0174] In the above embodiment, the case where the expander motor 42 operates at a constant operating frequency (motor speed) (i.e., the expander motor 42 operates at the same operating frequency during initial cooling and steady-state operation) has been described as an example, but the present invention is not limited to this. The cryogenic refrigerator 10 may also include an expander motor 42 with a variable operating frequency, which can perform so-called accelerated cooling during the initial cooling period by operating the expander motor 42 at a frequency higher than that during steady-state operation. In this case, as described above... Figure 7 and Figure 8 As explained, the switching from initial cooling (accelerated cooling) to steady-state operation and the change in operating frequency can be based on the pressure of buffer volume 70 or the pressure difference between high-pressure line 63 and low-pressure line 64. By implementing accelerated cooling, the initial cooling time can be further shortened.

[0175] Pressure sensors such as the first pressure sensor 54 and the second pressure sensor 55 do not necessarily have to be installed on the compressor 12. They can also be installed at any location capable of measuring pressure, such as the gas line 62 or the expander 14. For example, the first pressure sensor 54 can be installed at any location on the high-pressure line 63, and the second pressure sensor 55 can be installed at any location on the low-pressure line 64.

[0176] In the above embodiment, the supply valve 72 and the recovery valve 74 are each provided as separate valves and are respectively connected to the buffer volume 70, but the present invention is not limited thereto. For example, the supply valve 72 and the recovery valve 74 can be integrated, for example, they can be a three-way valve connected to the buffer volume 70. The supply state of connecting the buffer volume 70 to the low-pressure line 64 and the recovery state of connecting the buffer volume 70 to the high-pressure line 63 can be switched by switching the three-way valve.

[0177] In the above embodiment, the buffer volume 70 is a single buffer tank, but in one embodiment, the buffer volume 70 may also be multiple buffer tanks. One buffer tank can be connected to the low-pressure line 64 via the supply valve 72, and the other buffer tanks can be connected to the high-pressure line 63 via the recovery valve 74. Furthermore, in the above embodiment, the buffer volume 70 is disposed outside the compressor 12 and the expander 14, but it is not limited to this. For example, the buffer volume 70 may also be disposed inside the compressor 12.

[0178] In the above embodiments, the case of a two-stage GM refrigerator 10 as the cryogenic refrigerator 10 was described as an example, but it is not limited to this. The cryogenic refrigerator 10 can also be a single-stage or multi-stage GM refrigerator, and it can also be other types of cryogenic refrigerators such as pulse tube refrigerators.

[0179] The embodiments of the present invention can also be described as follows.

[0180] 1. An ultra-low temperature refrigerator, characterized in that it comprises:

[0181] An expander capable of performing initial cooling from an initial temperature to an ultra-low temperature and then maintaining steady-state operation at the ultra-low temperature following the initial cooling;

[0182] A high-pressure pipeline is connected to the expander and through which the working gas drawn in by the expander flows;

[0183] A low-pressure pipeline is connected to the expander and through which the working gas discharged from the expander flows;

[0184] The first pressure sensor measures the pressure in the high-pressure pipeline;

[0185] Buffer volume for storing working gas;

[0186] A supply valve connects the buffer volume to the low-pressure pipeline; and

[0187] The controller controls the supply valve based on the pressure of the high-pressure line measured by the first pressure sensor during the initial cooling period, so as to keep the pressure of the high-pressure line within a preset appropriate pressure range.

[0188] 2. The cryogenic refrigerator according to item 1, characterized in that,

[0189] The controller is configured to compare the measured pressure of the high-pressure line with the lower limit of the appropriate pressure range during the initial cooling period, and to actuate the supply valve to repeatedly open and close it to prevent the pressure of the high-pressure line from falling below the lower limit.

[0190] 3. The cryogenic refrigerator according to item 1 or 2, characterized in that,

[0191] If the buffer volume is denoted as VB, the volume of the high-pressure pipeline as VH, the volume of the low-pressure pipeline as VL, the working gas sealing pressure at a certain temperature as PI, the pressure of the high-pressure pipeline in steady-state operation at that temperature as PH, and the pressure of the low-pressure pipeline in steady-state operation at that temperature as PL, then at any temperature within the temperature range from the initial temperature to the ultra-low temperature, the buffer volume satisfies VB≥VH(PH-PI) / (PI-PL)-VL.

[0192] 4. The cryogenic refrigerator according to any one of items 1 to 3, characterized in that,

[0193] It also includes a recovery valve, which connects the buffer volume to the high-pressure pipeline.

[0194] The controller controls the recovery valve to maintain the pressure in the high-pressure pipeline within the appropriate pressure range.

[0195] 5. The cryogenic refrigerator according to item 4, characterized in that,

[0196] If the buffer volume is denoted as VB, the volume of the high-pressure pipeline as VH, the volume of the low-pressure pipeline as VL, the working gas sealing pressure at a certain temperature as PI, the pressure of the high-pressure pipeline in steady-state operation at that temperature as PH, and the pressure of the low-pressure pipeline in steady-state operation at that temperature as PL, then at any temperature within the temperature range from the initial temperature to the ultra-low temperature, the buffer volume satisfies VB≥-VH+VL(PI-PL) / (PH-PI).

[0197] 6. The cryogenic refrigerator according to any one of items 1 to 5, characterized in that,

[0198] It also includes a buffer pressure sensor that measures the pressure in the buffer volume.

[0199] The controller terminates the initial cooling based on the pressure of the buffer volume measured by the buffer pressure sensor.

[0200] 7. The cryogenic refrigerator according to any one of items 1 to 6, characterized in that,

[0201] It also includes a second pressure sensor, which measures the pressure in the low-pressure pipeline.

[0202] The controller is configured as follows:

[0203] When the pressure in the low-pressure pipeline, as measured by the second pressure sensor, is lower than a preset low-pressure threshold, the control of the supply valve based on the pressure in the high-pressure pipeline is interrupted.

[0204] The supply valve is controlled based on the pressure of the low-pressure pipeline measured by the second pressure sensor, so that the pressure of the low-pressure pipeline is restored to the low-pressure threshold.

[0205] 8. The cryogenic refrigerator according to item 7, characterized in that,

[0206] The controller is configured as follows:

[0207] When the pressure in the high-pressure line, as measured by the first pressure sensor, is lower than the first appropriate pressure range, the control of the compressor motor's operating frequency based on the pressure in the low-pressure line is interrupted.

[0208] The operating frequency of the compressor motor is controlled based on the pressure of the high-pressure pipeline measured by the first pressure sensor, so that the pressure of the high-pressure pipeline is restored to the first appropriate pressure range.

[0209] 9. The cryogenic refrigerator according to any one of claims 1 to 8, characterized in that it further comprises:

[0210] The first compressor is connected to the expander via the high-pressure pipeline and the low-pressure pipeline; and

[0211] The second compressor is installed on the high-pressure pipeline or the low-pressure pipeline and connected in series with the first compressor.

[0212] 10. The cryogenic refrigerator according to item 9, characterized in that,

[0213] The first compressor or the second compressor has a compressor motor with a variable operating frequency and is driven by the compressor motor.

[0214] The controller is configured to control the operating frequency of the compressor motor based on the pressure of the high-pressure line measured by the first pressure sensor during the initial cooling period, so as to keep the pressure of the high-pressure line within the appropriate pressure range.

[0215] 11. A method for operating an ultra-low temperature refrigerator, the ultra-low temperature refrigerator comprising a first compressor, an expander, a high-pressure pipeline and a low-pressure pipeline connecting the first compressor and the expander, characterized in that,

[0216] The operating method includes the following steps:

[0217] The second compressor is installed on the high-pressure pipeline or the low-pressure pipeline and connected in series with the first compressor;

[0218] The buffer volume is connected to the low-pressure pipeline via a supply valve;

[0219] With the second compressor and the buffer volume connected to the cryogenic refrigerator, initial cooling is performed to cool the expander from its initial temperature to the cryogenic temperature; and

[0220] After the initial cooling, the expander is maintained in a steady-state operation at the ultra-low temperature.

[0221] Performing the initial cooling includes the following steps:

[0222] The first compressor and the second compressor are used to supply working gas to the expander; and

[0223] The supply valve is controlled based on the measured pressure of the high-pressure pipeline to maintain the pressure of the high-pressure pipeline within a preset appropriate pressure range.

[0224] 12. The method according to item 11, characterized in that it further comprises the following steps:

[0225] The second compressor is disassembled after the initial cooling.

[0226] 13. The method according to item 11 or 12, characterized in that it further comprises the following steps:

[0227] The buffer volume is disassembled after the initial cooling.

[0228] 14. The method according to any one of items 11 to 13, characterized in that,

[0229] Performing the initial cooling includes the following steps:

[0230] When the measured pressure in the low-pressure pipeline is lower than a preset low-pressure threshold, the control of the supply valve based on the pressure in the high-pressure pipeline is interrupted; and

[0231] The supply valve is controlled based on the measured pressure of the low-pressure line so that the pressure of the low-pressure line is restored to the low-pressure threshold.

[0232] 15. The method according to item 14, characterized in that,

[0233] Performing the initial cooling includes the following steps:

[0234] When the measured pressure in the high-pressure pipeline is lower than the high-pressure threshold, the control of the supply valve based on the pressure in the low-pressure pipeline is interrupted; and

[0235] The supply valve is controlled based on the measured pressure of the high-pressure pipeline to restore the pressure of the high-pressure pipeline to the high-pressure threshold.

[0236] 16. The method according to any one of items 11 to 15, characterized in that,

[0237] The first compressor or the second compressor has a compressor motor with a variable operating frequency and is driven by the compressor motor.

[0238] The initial cooling process includes the following steps: controlling the operating frequency of the compressor motor based on the measured pressure of the high-pressure pipeline, so that the pressure of the high-pressure pipeline is maintained within a pre-set appropriate pressure range.

[0239] 17. The method according to any one of items 11 to 16, characterized in that,

[0240] Performing the initial cooling includes the following steps:

[0241] The pressure of the buffer volume was measured during the initial cooling period; and

[0242] The initial cooling is terminated based on the measured pressure of the buffer volume.

[0243] 18. A method for operating an ultra-low temperature refrigerator, the ultra-low temperature refrigerator comprising a first compressor, an expander, a high-pressure pipeline connecting the first compressor to the expander, and a low-pressure pipeline, characterized in that,

[0244] The operating method includes the following steps:

[0245] The second compressor is installed on the high-pressure pipeline or the low-pressure pipeline and connected in series with the first compressor;

[0246] With the second compressor connected to the cryogenic refrigerator, initial cooling is performed to cool the expander from its initial temperature to the cryogenic temperature; and

[0247] After the initial cooling, the expander is maintained in a steady-state operation at the ultra-low temperature.

[0248] The first compressor or the second compressor has a compressor motor with a variable operating frequency and is driven by the compressor motor.

[0249] Performing the initial cooling includes the following steps:

[0250] The first compressor and the second compressor are used to supply working gas to the expander; and

[0251] The operating frequency of the compressor motor is controlled based on the measured pressure of the high-pressure pipeline, so that the pressure of the high-pressure pipeline is maintained within a preset appropriate pressure range.

[0252] 19. The method according to item 18, characterized in that it further comprises the following steps:

[0253] The second compressor is disassembled after the initial cooling.

[0254] 20. The method according to item 18 or 19, characterized in that it further comprises the following steps:

[0255] The buffer volume is connected to the low-pressure pipeline via a supply valve.

[0256] Performing the initial cooling includes the following steps:

[0257] The supply valve is controlled based on the measured pressure of the high-pressure pipeline to maintain the pressure of the high-pressure pipeline within a preset appropriate pressure range.

[0258] 21. The method according to item 20, characterized in that it further comprises the following steps:

[0259] The buffer volume is disassembled after the initial cooling.

[0260] 22. The method according to item 20 or 21, characterized in that,

[0261] Performing the initial cooling includes the following steps:

[0262] The pressure of the buffer volume was measured during the initial cooling period; and

[0263] The initial cooling is terminated based on the measured pressure of the buffer volume.

[0264] The present invention has been described above with reference to the embodiments. Those skilled in the art should understand that the present invention is not limited to the above-described embodiments, and various design changes and modifications are possible, and such modifications are also within the scope of the present invention.

Claims

1. A method for operating an ultra-low temperature refrigerator, the ultra-low temperature refrigerator comprising a first compressor, an expander, a high-pressure pipeline connecting the first compressor to the expander, and a low-pressure pipeline, the method being characterized in that the method includes the following steps: The second compressor is installed on the high-pressure pipeline or the low-pressure pipeline and connected in series with the first compressor; The buffer volume is connected to the low-pressure pipeline via a supply valve; With the second compressor and the buffer volume connected to the cryogenic refrigerator, initial cooling is performed to cool the expander from its initial temperature to the cryogenic temperature; and Following the initial cooling, the expander is then kept in a steady-state operation at the ultra-low temperature. in, Performing the initial cooling includes the following steps: The first compressor and the second compressor are used to supply working gas to the expander; and The supply valve is controlled based on the measured pressure of the high-pressure pipeline to maintain the pressure of the high-pressure pipeline within a preset appropriate pressure range.

2. The method according to claim 1, characterized in that, It also includes the following processes: The second compressor is disassembled after the initial cooling.

3. The method according to claim 1 or 2, characterized in that, It also includes the following processes: The buffer volume is disassembled after the initial cooling.

4. The method according to claim 1 or 2, characterized in that, Performing the initial cooling includes the following steps: When the measured pressure in the low-pressure pipeline is lower than a preset low-pressure threshold, the control of the supply valve based on the pressure in the high-pressure pipeline is interrupted; and The supply valve is controlled based on the measured pressure of the low-pressure line so that the pressure of the low-pressure line is restored to the low-pressure threshold.

5. The method according to claim 4, characterized in that, Performing the initial cooling includes the following steps: When the measured pressure in the high-pressure pipeline is lower than the high-pressure threshold, the control of the supply valve based on the pressure in the low-pressure pipeline is interrupted; and The supply valve is controlled based on the measured pressure of the high-pressure pipeline to restore the pressure of the high-pressure pipeline to the high-pressure threshold.

6. A method for operating an ultra-low temperature refrigerator, the ultra-low temperature refrigerator comprising a first compressor, an expander, a high-pressure pipeline connecting the first compressor to the expander, and a low-pressure pipeline, the method being characterized in that... The method includes the following steps: The second compressor is installed on the high-pressure pipeline or the low-pressure pipeline and connected in series with the first compressor; With the second compressor connected to the cryogenic refrigerator, initial cooling is performed to cool the expander from its initial temperature to the cryogenic temperature; and Following the initial cooling, the expander is then kept in a steady-state operation at the ultra-low temperature. The first compressor or the second compressor has a compressor motor with a variable operating frequency and is driven by the compressor motor. Performing the initial cooling includes the following steps: The first compressor and the second compressor are used to supply working gas to the expander; and The operating frequency of the compressor motor is controlled based on the measured pressure of the high-pressure pipeline, so that the pressure of the high-pressure pipeline is maintained within a preset appropriate pressure range.

7. The method according to claim 6, characterized in that, It also includes the following processes: The second compressor is disassembled after the initial cooling.

8. The method according to claim 6 or 7, characterized in that, It also includes the following processes: The buffer volume is connected to the low-pressure pipeline via a supply valve. Performing the initial cooling includes the following steps: The supply valve is controlled based on the measured pressure of the high-pressure pipeline to maintain the pressure of the high-pressure pipeline within a preset appropriate pressure range.

9. The method according to claim 8, characterized in that, It also includes the following processes: The buffer volume is disassembled after the initial cooling.

10. An ultra-low temperature refrigerator, characterized in that, have: An expander capable of performing initial cooling from an initial temperature to an ultra-low temperature and then maintaining steady-state operation at the ultra-low temperature following the initial cooling; High-pressure pipelines and low-pressure pipelines are connected to the expander; The first pressure sensor measures the pressure in the high-pressure pipeline; The second pressure sensor measures the pressure in the low-pressure pipeline; Buffer volume for storing working gas; A supply valve connects the buffer volume to the low-pressure pipeline; and The controller is configured to control the supply valve based on the pressure of the high-pressure line measured by the first pressure sensor during the initial cooling period, so as to maintain the pressure of the high-pressure line within a preset appropriate pressure range. The controller is further configured as follows: When the pressure in the low-pressure pipeline, as measured by the second pressure sensor, is lower than a preset low-pressure threshold, the control of the supply valve based on the pressure in the high-pressure pipeline is interrupted. The supply valve is controlled based on the pressure of the low-pressure pipeline measured by the second pressure sensor, so that the pressure of the low-pressure pipeline is restored to the low-pressure threshold.

11. The cryogenic refrigerator according to claim 10, characterized in that, The controller is configured as follows: When the pressure in the high-pressure line, as measured by the first pressure sensor, is lower than the high-pressure threshold, the control of the supply valve based on the pressure in the low-pressure line is interrupted. The supply valve is controlled based on the pressure of the high-pressure pipeline measured by the first pressure sensor, so that the pressure of the high-pressure pipeline is restored to the high-pressure threshold.

12. The cryogenic refrigerator according to claim 10 or 11, characterized in that, It also has: The first compressor is connected to the expander via the high-pressure pipeline and the low-pressure pipeline; and The second compressor is installed on the high-pressure pipeline or the low-pressure pipeline and connected in series with the first compressor.

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