Cryocooler and method for monitoring a cryocooler

Abstract

An ultra-low temperature refrigerator (10) is capable of performing a steady state operation and a cooling operation before the steady state operation. The ultra-low temperature refrigerator (10) is provided with: an expander motor (42) that causes an expander (14) of the ultra-low temperature refrigerator (10) to operate; an inverter (90) configured to control an operating frequency of the expander motor (42) and capable of operating in a manner that drives the expander motor (42) at an operating frequency lower than an operating frequency in the cooling operation; a current sensor (50) that measures a current supplied from the inverter (90) to the expander motor (42) and outputs a motor current signal indicative of the current; and a processing portion (100) that monitors the expander motor (42) based on at least the motor current signal in the steady state operation.

Description

Technical Field

[0001] This invention relates to an ultra-low temperature refrigerator and a monitoring method for the ultra-low temperature refrigerator. Background Technology

[0002] Previously, the following technology was known: In order to shorten the cooling descent time when starting a cryogenic refrigerator, the speed of the expander's drive motor is increased using a frequency converter. During this startup operation, if an abnormal change is detected in the motor current, the motor speed decreases, thereby protecting the drive motor.

[0003] Previous technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 3-152353 Summary of the Invention

[0006] The technical problem to be solved by the invention

[0007] During long-term operation of a cryogenic refrigerator, the load applied to the drive motor of the expander will gradually increase. Exceeding the motor's specifications may cause abnormal actions or malfunctions such as motor runaway, abnormal noise from the cryogenic refrigerator, or hinder the normal operation of the cryogenic refrigerator.

[0008] One exemplary objective of one embodiment of the present invention is to provide an ultra-low temperature refrigerator and its monitoring method that helps to predict or prevent abnormal operation or failure of the expander motor caused by long-term operation.

[0009] means for solving technical problems

[0010] According to one embodiment of the present invention, a cryogenic refrigerator is provided capable of performing steady-state operation and cooling operation prior to steady-state operation. The cryogenic refrigerator includes: an expander motor for operating the expander of the cryogenic refrigerator; a frequency converter configured to control the operating frequency of the expander motor, and capable of driving the expander motor at an operating frequency lower than the operating frequency of the cooling operation during steady-state operation; a current sensor for measuring the current supplied from the frequency converter to the expander motor and outputting a motor current signal representing the current; and a processing unit for monitoring the expander motor at least based on the motor current signal during steady-state operation.

[0011] According to one embodiment of the present invention, a monitoring method for a cryogenic refrigerator is provided. The cryogenic refrigerator is capable of performing steady-state operation and a cooling operation prior to steady-state operation, and includes: an expander motor for operating the expander of the cryogenic refrigerator; and a frequency converter configured to control the operating frequency of the expander motor, and capable of driving the expander motor at an operating frequency lower than the operating frequency of the cooling operation during steady-state operation. The method includes the steps of: measuring the current supplied from the frequency converter to the expander motor; and monitoring the expander motor at least based on the current of the expander motor during steady-state operation.

[0012] According to one embodiment of the present invention, an ultra-low temperature refrigerator is provided, comprising: an expander motor for operating the expander of the ultra-low temperature refrigerator; a frequency converter configured to control the operating frequency of the expander motor; and a processing unit for monitoring the expander motor based on a power consumption signal indicating the power consumption of the frequency converter or the expander motor.

[0013] According to one embodiment of the present invention, a monitoring method for a cryogenic refrigerator is provided. The cryogenic refrigerator includes: an expander motor for operating the expander of the cryogenic refrigerator; and a frequency converter configured to control the operating frequency of the expander motor. The method includes the following steps: acquiring the power consumption of the frequency converter or the expander motor; and monitoring the expander motor based on the acquired power consumption.

[0014] Furthermore, any combination of the above-mentioned constituent elements, or the substitution of the constituent elements or descriptions of the present invention among methods, apparatuses, systems, etc., are also valid embodiments of the present invention.

[0015] Invention Effects

[0016] According to the present invention, an ultra-low temperature refrigerator and its monitoring method are provided that help predict or prevent abnormal operation or failure of the expander motor caused by long-term operation. Attached Figure Description

[0017] Figure 1 This is a diagram that roughly illustrates the cryogenic refrigerator involved in the implementation method.

[0018] Figure 2 This is a diagram that roughly illustrates the cryogenic refrigerator involved in the implementation method.

[0019] Figure 3 It is a graph showing the relationship between the effective value of the current flowing through the expander motor and the load duty cycle for multiple operating frequencies.

[0020] Figure 4 This is an example illustrating the relationship between the operating frequency of the expander motor and the current threshold in the embodiment.

[0021] Figure 5 This is a block diagram of the motor monitoring device involved in the implementation method.

[0022] Figure 6 This is a flowchart illustrating the monitoring method for the cryogenic refrigerator involved in the implementation method.

[0023] Figure 7 This is a block diagram of the motor monitoring device involved in the implementation method.

[0024] Figure 8 It is a graph showing the relationship between the power consumption of a frequency converter and the load duty cycle at multiple operating frequency values.

[0025] Figure 9 This is a block diagram of a motor monitoring device according to another embodiment.

[0026] Figure 10 This is a flowchart illustrating a monitoring method for an ultra-low temperature refrigerator according to another embodiment. Detailed Implementation

[0027] 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.

[0028] Figure 1 and Figure 2 This is a diagram that schematically illustrates the cryogenic refrigerator 10 involved in the embodiment. Figure 1 The appearance of the cryogenic refrigerator 10 is shown in the figure. Figure 2 The internal structure of the cryogenic refrigerator 10 is shown. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator.

[0029] The cryogenic refrigerator 10 includes a compressor 12 and an expander 14. The cryogenic refrigerator 10 also includes a monitoring device for monitoring the expander motor 42 that drives the expander 14. This monitoring device includes a current sensor 50 and a processing unit 100 (details will be described later).

[0030] The compressor 12 is configured to recover the working gas from the expander 14 of the cryogenic refrigerator 10, and after pressurizing the recovered working gas, supply it back to the expander 14. The working gas is also known as the refrigerant gas, which is usually helium, but other suitable gases may also be used.

[0031] 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 are 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.

[0032] The compressor 12 has a compressor body 22 and a compressor frame 23 that houses the compressor body 22. The compressor 12 is also referred to as a compressor unit.

[0033] The compressor body 22 is configured to internally compress the working gas drawn in from its inlet and discharge it from its outlet. The compressor body 22 can be, for example, a scroll pump, a rotary pump, or other pump that pressurizes the working gas. The compressor body 22 can also be configured to discharge a constant flow rate of working gas. Alternatively, the compressor body 22 can be configured to allow a variable flow rate of the discharged working gas. The compressor body 22 is sometimes referred to as a compression chamber.

[0034] The compressor 12 may also have a compressor controller 24 for controlling the compressor 12. The compressor controller 24 can not only control the compressor 12, but also centrally control the cryogenic refrigerator 10, for example, it can also control the expander 14 (e.g., expander motor 42). The compressor controller 24 can be installed on the compressor 12, for example, it can be disposed on the outer surface of the compressor housing 23, or it can be housed in the compressor housing 23. Alternatively, the compressor controller 24 can also be configured in a separate position from the compressor 12, and connected to the compressor 12, for example, via a control signal line.

[0035] The expander 14 includes a refrigeration cylinder 16 and a displacement assembly 18. The refrigeration cylinder 16 guides the linear reciprocating motion of the displacement assembly 18 and forms expansion chambers 32 and 34 for the working gas between itself 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The first displacement device 18a is housed in the first cylinder 16a, and the second displacement device 18b is housed in the second cylinder 16b. The first displacement device 18a is axially reciprocating along the first cylinder 16a, and the second displacement device 18b is axially reciprocating along the second cylinder 16b.

[0040] 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 in the first displacement device 18a.

[0041] 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 may also be formed in granular form. The upper and lower cover portions of the second displacement device 18b may 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 may 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.

[0042] 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.

[0043] The first cold 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 accumulator 28 is connected to the first cold accumulator 26 via a working gas flow path 36c formed from the lower cover of the first displacement device 18a to the upper cover of the second displacement device 18b. Furthermore, the second cold 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.

[0044] 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.

[0045] like Figure 1As 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.

[0046] 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., when one valve is open, the other valve is closed).

[0047] 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 manner 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.

[0048] 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.

[0049] The expander 14 includes an expander motor 42 and a motion conversion mechanism 43. 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 in the refrigerator housing 20.

[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 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 unit 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] In addition, the cryogenic refrigerator 10 is powered by a power source 46, such as a commercial power supply (three-phase AC power). The power source 46 is connected to the compressor 12 and the expander motor 42 via a power supply wiring 48. Since the expander motor 42 is connected to the power source 46 via the compressor 12, the compressor 12 can also be considered as the power source for the expander motor 42. Alternatively, the compressor 12 and the expander motor 42 can be connected to separate power sources.

[0052] The expander motor 42 is, for example, a permanent magnet motor driven by three-phase AC power. The operating frequency of the expander motor 42 is controlled by a frequency converter 90. The frequency converter 90 is located on the power supply line 48. The expander motor 42 is capable of operating at a speed corresponding to the operating frequency of the expander motor 42, which is equivalent to the output frequency of the inverter 90. As an example, the output frequency of the frequency converter 90 can vary in the range of 30Hz to 100Hz, or in the range of 40Hz to 70Hz.

[0053] A current sensor 50 is connected to the expander motor 42 to measure the current supplied from the inverter 90 to the expander motor 42 during at least steady-state operation of the cryogenic refrigerator 10. The current sensor 50 is located on the power supply wiring 48 between the inverter 90 and the expander motor 42.

[0054] Furthermore, the current sensor 50 is configured to output a motor current signal S1, representing the measured current, to the processing unit 100. The motor current signal S1 can be a signal representing the effective value of the current supplied to the expander motor 42. The current sensor 50 is communicatively connected to the processing unit 100 via a wired or wireless means. The current sensor 50 can also be a three-phase ammeter that simultaneously measures the three-phase current flowing through the expander motor 42, or it can be other types of current sensors that measure the current flowing through the expander motor 42. For example, the current sensor 50 can also be configured to simultaneously measure the three-phase current output from the inverter 90 to the expander motor 42, and output, for example, a voltage signal representing the magnitude of each of the measured three-phase currents, as the motor current signal S1 to the processing unit 100. The motor current signal S1 can be current waveform data representing the time variation of the current flowing through the expander motor 42 during the operation of the cryogenic refrigerator 10.

[0055] The inverter 90 is configured to output output frequency information S2, representing the output frequency of the inverter 90 (i.e., the operating frequency of the expander motor 42), to the processing unit 100. Alternatively, the processing unit 100 may calculate the output frequency information S2 based on the motor current signal S1 input from the current sensor 50, thereby receiving the output frequency information S2 from the inverter 90 instead of the processing unit 100. For example, the processing unit 100 may calculate the operating frequency of the expander motor 42 by counting the number of current peaks per unit time based on the waveform of the current flowing through the expander motor 42. Alternatively, the inverter 90 may also include the current sensor 50 (the inverter 90 may also have the function of measuring output current), and the processing unit 100 may obtain the motor current signal S1 from the inverter 90. As the motor current signal S1, the effective value of the current output by the inverter 90 for controlling the expander motor 42 is used.

[0056] The processing unit 100 is configured to receive the motor current signal S1 from the current sensor 50 (or the inverter 90) and monitor the expander motor 42 based on the motor current signal S1 during at least steady-state operation of the cryogenic refrigerator 10. Details of the processing unit 100 will be described later.

[0057] In the illustrated example, the current sensor 50, the frequency converter 90, and the processing unit 100 are integrated into the compressor controller 24 and mounted on the compressor 12, but this is not the only possibility. The current sensor 50, the frequency converter 90, and the processing unit 100 may also be mounted on the expander 14 (e.g., mounted on the expander motor 42), or on other parts of the power supply wiring 48.

[0058] 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.

[0059] 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 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.

[0060] 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).

[0061] The cryogenic refrigerator 10 is capable of performing steady-state operation and a cooling operation prior to steady-state operation. The cooling operation is an operating mode in which the cryogenic refrigerator 10 is rapidly cooled from room temperature to cryogenic temperature upon startup. The steady-state operation is an operating mode in which the cryogenic refrigerator 10 maintains its cryogenic state achieved through the cooling operation. The cryogenic refrigerator 10 is cooled to a standard cooling temperature through the cooling operation and maintained within the permissible temperature range of cryogenic temperature, 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 applications involving the cooling of 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, approximately 10 K to 20 K, or below 10 K.

[0062] The switching from cooling operation to steady-state operation can be controlled by a controller (e.g., compressor controller 24) that controls the cryogenic refrigerator 10. The cryogenic refrigerator 10 may also include a temperature sensor 52 that 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. The compressor controller 24 compares the measured temperature of the second cooling stage 35 with a standard cooling temperature (or the aforementioned permissible temperature range) based on the measured temperature signal from the temperature sensor 52. If the measured temperature is higher than the standard cooling temperature, cooling operation is performed; if the measured temperature is lower than the standard cooling temperature, the cooling operation is switched to steady-state operation.

[0063] The inverter 90 is capable of operating as follows: driving the expander motor 42 at a lower operating frequency than during cooling operation in steady-state operation. For example, under the control of a controller (e.g., compressor controller 24), the inverter 90 can drive the expander motor 42 at a preset first operating frequency during cooling operation and at a preset second operating frequency during steady-state operation. However, the second operating frequency is lower than the first operating frequency. The controller can control the expander motor 42 based on the measured temperature signal from the temperature sensor 52 and a preset operating frequency curve, which can be set such that a higher measured temperature results in a higher operating frequency.

[0064] Alternatively, the controller (e.g., compressor controller 24) can control the output frequency of the inverter 90 based on the measured temperature signal from the temperature sensor 52 to minimize the deviation between the measured temperature and the standard cooling temperature (e.g., based on feedback control such as PID control). Therefore, when the measured temperature of the temperature sensor 52 is higher than the standard cooling temperature, the operating frequency of the expander motor 42 increases; when the measured temperature of the temperature sensor 52 is lower than the standard cooling temperature, the operating frequency of the expander motor 42 decreases. Thus, during cooling operation, the initial measured temperature is room temperature, at which point the operating frequency of the expander motor 42 is high, thereby achieving rapid cooling. The operating frequency decreases as the temperature drops towards the standard cooling temperature. In steady-state operation, for example, when external disturbances such as heat intrusion from the surroundings cause the measured temperature to become higher than the standard cooling temperature, the operating frequency of the expander motor 42 increases, thereby cooling back to the standard cooling temperature. Conversely, for example, when the measured temperature becomes lower than the standard cooling temperature due to a decrease in heat load, the operating frequency of the expander motor 42 decreases, thereby returning to the standard cooling temperature. Thus, overcooling can be avoided, thereby maintaining the standard cooling temperature.

[0065] Furthermore, during the long-term operation of the cryogenic refrigerator 10, the load applied to the expander motor 42 tends to gradually increase. One possible reason for this is that various particles from the lubricating oil or cold storage material within the compressor 12 accumulate within the expander 14, leading to increased pressure loss within the expander 14. Consequently, the load applied to the expander motor 42 gradually increases with the outflow / inflow of working gas relative to the expansion chamber. Another possible reason is that moisture is absorbed by the displacement device within the expander 14, causing it to expand slightly and reducing the gap between it and the cylinder block. This results in increased sliding resistance of the displacement device.

[0066] Therefore, if the drive load on the expander motor 42 becomes high, the risk of applying a load torque exceeding the motor's specifications (e.g., instantaneous maximum torque or other rated torque) to the expander motor 42 increases. A load exceeding the specifications of the expander motor 42 may cause abnormal operation or malfunction such as runaway of the expander motor 42, abnormal noise from the expander 14, or hinder the normal operation of the expander 14.

[0067] By monitoring the current flowing through the expander motor 42 and detecting abnormal fluctuations in the current accompanying abnormalities in the expander motor 42, it is possible to identify the occurrence of abnormalities in the expander motor 42. However, when the operating frequency (speed) of the expander motor 42 is controlled by the frequency converter 90, the motor current will fluctuate not only when the expander motor 42 malfunctions, but also when the operating frequency changes during normal operation. Furthermore, when the expander 14 is placed in a strong magnetic field environment, if an external magnetic field acts on the expander motor 42, the motor current will also fluctuate according to the magnitude of the magnetic field. The motor current will also fluctuate when the input voltage of the frequency converter 90 changes. Since the motor current can fluctuate according to various operating conditions of the expander motor 42, it is not easy to distinguish between abnormal fluctuations in the current accompanying abnormalities in the expander motor 42 and current fluctuations caused by changes in operating conditions during normal operation of the expander motor 42.

[0068] Figure 3 This is a graph showing the relationship between the effective value of the current flowing through the expander motor 42 and the load duty cycle, measured for multiple operating frequencies. The vertical axis represents the effective value of the current supplied from the inverter 90 to the expander motor 42 and measured by the current sensor 50. The horizontal axis, representing the load duty cycle, indicates the ratio (%) of the actual load torque acting on the expander motor 42 to the maximum allowable load torque (e.g., instantaneous maximum torque) of the expander motor 42. Therefore, when the load duty cycle exceeds 100%, abnormal operation such as runaway occurs in the expander motor 42, or the probability of abnormal operation is high.

[0069] Depend on Figure 3 It can be seen that, given a certain load duty cycle (which can be any value, such as 90%), the inverter controls the motor current in a way that keeps the motor current value almost the same at both 40Hz and 50Hz operating frequencies. Thus, at lower operating frequencies, the dependence of the motor current value on the operating frequency is almost invisible. On the other hand, in Figure 3 In the example, within the operating frequency range of 50Hz to 70Hz, the motor current decreases as the operating frequency increases. Thus, at relatively high operating frequencies, the motor current exhibits frequency dependence, and the motor current value may vary depending on the operating frequency.

[0070] Next, for a given operating frequency, the change in motor current value as the load duty cycle changes was observed. It can be seen that, regardless of the operating frequency, although the motor current value is different, the motor current value tends to increase as the load duty cycle increases.

[0071] Therefore, at a certain operating frequency (e.g., 60Hz), the motor current value when the load duty cycle is less than 100% and sufficiently large (e.g., 90%–98%) can be used as the current threshold. When a current exceeding this current threshold flows through the expander motor 42 (i.e., when measured by the current sensor 50), a large load corresponding to that load duty cycle is applied to the expander motor 42. This can be considered as a prediction of abnormal operation of the expander motor 42, thereby enabling the implementation of countermeasures to prevent abnormal operation in advance, such as issuing warnings, reducing the operating frequency, or stopping the operation of the cryogenic refrigerator 10.

[0072] However, when the expander motor 42 is driven at a higher operating frequency (e.g., 70Hz), the motor current value becomes considerably smaller than that at 60Hz, failing to reach the current threshold set for 60Hz. Therefore, comparing the motor current value of the expander motor 42 operating at 70Hz with the threshold for 60Hz does not yield effective results for predicting anomalies in the expander motor 42. Conversely, when the expander motor 42 is driven at a lower operating frequency (e.g., 50Hz), the motor current value becomes considerably larger than that at 60Hz, causing even a relatively small load duty cycle to exceed the current threshold set for 60Hz. Comparing the motor current value of the expander motor 42 operating at 50Hz with the threshold for 60Hz again does not yield effective results for predicting anomalies in the expander motor 42.

[0073] Therefore, when the operating frequency of the expander motor 42 is controlled by the frequency converter 90, if only one current threshold is set, it is difficult to predict or prevent abnormal operation or malfunction of the expander motor 42 by monitoring the current flowing through the expander motor 42. Therefore, in this embodiment, current thresholds are set for multiple values ​​of the operating frequency of the expander motor 42. Figure 4 The example illustrates these multiple current thresholds.

[0074] Figure 4 This illustrates an example of the relationship between the operating frequency and current threshold of the expander motor 42 involved in the embodiment. Figure 4 The figure shows the results at specific load duty cycle values ​​(specifically, load duty cycles of 90% and 95%). Figure 3 The diagram shows the relationship between the motor current value corresponding to the operating frequency and the load duty cycle. Therefore, as mentioned above, when the operating frequency is relatively low ( Figure 4 Within the operating frequency range of 40Hz to 50Hz, the motor current value remains roughly constant. At higher operating frequencies ( Figure 4 Within the operating frequency range of 50Hz to 70Hz, the motor current decreases as the operating frequency increases. Figure 4 It can be seen that if the load duty cycle increases, the motor current will increase.

[0075] Figure 4 The relationship between the operating frequency and current threshold of the expander motor 42 shown can also be used as an example of the operating frequency / current threshold table 62 described later. When the combination of the operating frequency value and the measured motor current value is located in the upper region of the graph (i.e., when the expander motor 42 is driven at that operating frequency and the current value measured by the current sensor 50 exceeds the current threshold corresponding to that operating frequency), abnormal operation of the expander motor 42 can be considered a prediction. When the combination of the operating frequency value and the measured motor current value is located in the lower region of the graph, since the measured current value does not exceed the current threshold, it can be considered that no abnormality will occur.

[0076] Therefore, by establishing corresponding relationships between multiple current threshold values ​​and multiple values ​​of the operating frequency of the expander motor 42, even when the operating frequency of the expander motor 42 is controlled by the frequency converter 90, it is possible to accurately determine the actual occurrence or high probability of abnormal actions such as runaway. Thus, countermeasures can be taken to prevent such abnormal actions of the expander motor 42 in advance.

[0077] Depending on the application of the cryogenic refrigerator 10 (e.g., for cooling superconducting electromagnets), the expander 14 is sometimes used in a strong magnetic field environment. In this case, the external magnetic field acting on the expander motor 42 will affect the operation of the expander motor 42, potentially causing fluctuations in the current flowing through it. According to the inventors' research, at a given operating frequency and a given load duty cycle, the motor current value tends to increase with the increase of the external magnetic field. This trend is particularly evident when the expander motor 42 is a permanent magnet motor. As an exemplary operating condition, when the operating frequency is 50 Hz or 60 Hz and the load duty cycle is 90% or more, the motor current value increases by approximately 5% to 10% when the external magnetic field is 500 Gauss, compared to when the external magnetic field is 0 Gauss.

[0078] Furthermore, typically, in the specifications of the cryogenic refrigerator 10, the input voltage flowing from the power supply 46 to the inverter 90 is allowed to vary to some extent (e.g., ±10%). When the input voltage flowing to the inverter 90 varies, the current flowing through the expander motor 42 also varies. According to the inventors' research, at a given operating frequency and a given load duty cycle, as the input voltage increases from a voltage value below a specified voltage value (e.g., 200V) of the power supply 46 to that specified voltage value, the motor current tends to increase.

[0079] Therefore, in addition to the operating frequency of the expander motor 42, multiple current thresholds are also associated with multiple values ​​of the operating conditions of the expander motor 42, such as external magnetic fields or input voltage. This allows for a good assessment of situations where the expander motor 42 may malfunction, and enables the implementation of countermeasures to prevent such malfunctions in advance.

[0080] Figure 5 This is a block diagram of a motor monitoring device according to an embodiment. The monitoring device includes a processing unit 100, which includes a current threshold setting unit 60 and a comparison unit 70. The current threshold setting unit 60 includes an operating frequency / current threshold table 62, an external magnetic field / current threshold table 64, and an input voltage / current threshold table 66. The monitoring device may also include a notification mechanism 80 that visually displays information indicating monitoring results; the notification mechanism 80 may include, for example, a display 82. The notification mechanism 80 may also announce diagnostic results audibly (e.g., through a speaker). The notification mechanism 80 may also send diagnostic results to a remote machine via a network such as the Internet.

[0081] The processing unit 100 is configured to monitor the expander motor 42 at least based on the motor current signal S1 during steady-state operation. Therefore, the processing unit 100 can obtain information indicating the current operating mode of the cryogenic refrigerator 10 from a controller (e.g., compressor controller 24) or determine the current operating mode based on the measured temperature signal S3 from the temperature sensor 52, and monitor the expander motor 42 based on the motor current signal S1 when the current operating mode is steady-state operation. Alternatively, the processing unit 100 can also monitor the expander motor 42 based on the motor current signal S1 when the current operating mode is cooling operation.

[0082] The processing unit 100 is configured to acquire a current threshold Th based on the operating conditions of the expander motor 42, and to monitor the expander motor 42 by comparing the current (e.g., the effective value of the current) of the expander motor 42 with the current threshold Th based on the motor current signal S1. Therefore, the current threshold setting unit 60 uses at least one of the following current threshold tables: operating frequency / current threshold table 62, external magnetic field / current threshold table 64, and input voltage / current threshold table 66, and acquires the current threshold Th based on the operating conditions of the expander motor 42 (e.g., motor current signal S1, output frequency information S2, the magnitude of the external magnetic field, and the input voltage flowing to the inverter 90, etc.).

[0083] Operating frequency / current threshold table 62 is a table that establishes a correspondence between multiple current thresholds and multiple values ​​of the operating frequency of the expander motor 42. External magnetic field / current threshold table 64 is a table that establishes a correspondence between multiple current thresholds and multiple values ​​of the external magnetic field applied to the expander motor 42. Input voltage / current threshold table 66 is a table that establishes a correspondence between multiple current thresholds and multiple values ​​of the input voltage flowing to the inverter 90. The operating frequency / current threshold table 62, external magnetic field / current threshold table 64, and input voltage / current threshold table 66 are preset and stored in the processing unit 100. These current threshold tables can be appropriately set based on the designer's experience or the designer's experiments or simulations.

[0084] For example, the current threshold setting unit 60 is configured to obtain a current threshold Th corresponding to the operating frequency based on the value of the operating frequency / current threshold table 62 and the operating frequency of the expander motor 42.

[0085] For example, such as Figure 4 As shown, the operating frequency / current threshold table 62 can establish a correspondence between multiple current thresholds and multiple values ​​of the operating frequency of the expander motor 42, respectively, in a manner that the current threshold decreases as the operating frequency increases in at least a portion of the range of operating frequencies of the expander motor 42 that can be controlled by the inverter 90 (e.g., the region on the high-frequency side of the range).

[0086] Furthermore, the operating frequency / current threshold table 62 can also establish a corresponding relationship between the current value of the expander motor 42 at that operating frequency value and the operating frequency value for each of the multiple values ​​of the operating frequency of the expander motor 42, when a load torque less than the maximum allowable load torque of the expander motor 42 is applied to the expander motor 42 by a specified amount (i.e., at a specified load duty cycle). The specified load duty cycle can be selected, for example, from a range of 80% or more and less than 100%, or from 90% or more and less than 98%.

[0087] Multiple operating frequency / current threshold tables 62 can be preset, and these multiple operating frequency / current threshold tables 62 can also be associated with multiple different load duty cycle values. The current threshold setting unit 60 can also obtain the current threshold Th corresponding to the operating frequency value based on the value of the operating frequency / current threshold table 62 selected from the multiple operating frequency / current threshold tables 62 and the operating frequency of the expander motor 42.

[0088] The current threshold setting unit 60 can be configured to obtain a current threshold Th corresponding to the value of the external magnetic field based on the external magnetic field / current threshold table 64 and the value of the external magnetic field applied to the expander motor 42. The value of the external magnetic field can be measured by a magnetic field sensor 54 mounted on the cryogenic refrigerator 10 (e.g., expander 14) or located nearby, and the measured value of the external magnetic field can be input to the processing unit 100 for use by the current threshold setting unit 60.

[0089] Alternatively, the processing unit 100 may be configured to obtain an estimate of the external magnetic field applied to the expander motor 42 based on the motor current signal S1, and to obtain a current threshold Th corresponding to the estimated external magnetic field based on the external magnetic field / current threshold table 64 and the estimated external magnetic field applied to the expander motor 42. According to the inventors' research, as long as the external magnetic field is inactive or sufficiently small, the three-phase current waveform flowing through the expander motor 42 exhibits symmetry; conversely, as the external magnetic field increases, the asymmetry of the three-phase current waveform tends to increase. For example, the deviation in the peak values ​​of the current waveforms between the three phases (U phase, V phase, W phase) can be cited as an example of this asymmetry. In particular, when the coil wiring of the expander motor 42 is star-connected, unbalanced currents are generated, thus the tendency to increase the asymmetry of the current waveform corresponding to the external magnetic field becomes significant. For example, based on the external magnetic field cause parameters (the maximum or minimum value of the peaks of the current waveforms of the U phase, V phase, and W phase, or the difference between the maximum and minimum values, etc.) that can be calculated from the motor current signal S1, an estimated value of the external magnetic field of the expander motor 42 can be obtained from the motor current signal S1.

[0090] The current threshold setting unit 60 can be configured to obtain a current threshold Th corresponding to the input voltage value based on the input voltage / current threshold table 66 and the value of the input voltage flowing to the inverter 90. Information indicating the value of the input voltage flowing to the inverter 90 can be input from the inverter 90 to the processing unit 100 for use by the current threshold setting unit 60.

[0091] Multiple external magnetic field / current threshold meters 64 can be preset, and these multiple external magnetic field / current threshold meters 64 can also be associated with values ​​of multiple different operating frequencies. That is, for example, a first and a second external magnetic field / current threshold meter 64 can be preset, and the first external magnetic field / current threshold meter 64 can be used when driving the expander motor 42 at a first operating frequency value (e.g., 70Hz), and the second external magnetic field / current threshold meter 64 can be used when driving the expander motor 42 at a second operating frequency value (e.g., 60Hz), which is different from the first operating frequency value. Similarly, multiple input voltage / current threshold meters 66 can also be preset, and these multiple input voltage / current threshold meters 66 can also be associated with values ​​of multiple different operating frequencies.

[0092] The comparison unit 70 compares the current (e.g., the effective value of the current) of the expander motor 42 with the acquired current threshold Th based on the motor current signal S1, and generates monitoring result data D1 based on the comparison result. The monitoring result data D1 is sent to the notification mechanism 80, and the monitoring result is displayed on the display 82, for example, to notify the user. In the event of a predicted abnormal operation of the expander motor 42, the notification mechanism 80 may also notify the user via an alarm sound. Alternatively, the monitoring result data D1 may be stored in the processing unit 100 so that it can be prompted to the user as needed.

[0093] The internal structure of the processing unit 100 is implemented in terms of hardware through components or circuits, such as a computer's CPU or memory, and in terms of software through computer programs, etc. However, the figures appropriately depict functional blocks that are implemented through their cooperation. Those skilled in the art should understand that these functional blocks can be implemented in various forms through a combination of hardware and software.

[0094] For example, the processing unit 100 can be implemented using a combination of a processor (hardware) such as a CPU (Central Processing Unit) or a microcomputer, and a software program executed by the processor (hardware). Such a hardware processor can be, for example, a programmable logic device such as an FPGA (Field Programmable Gate Array), or a control circuit like a programmable logic controller (PLC). The software program can also be a computer program used to monitor the cryogenic refrigerator 10 by causing the processing unit 100 to perform these functions.

[0095] Figure 6 This is a flowchart illustrating the monitoring method of the cryogenic refrigerator 10 according to the embodiment. First, as... Figure 6As shown, during the operation of the cryogenic refrigerator 10 (e.g., during steady-state operation), the current supplied from the inverter 90 to the expander motor 42 is measured using the current sensor 50 (S10). Then, the expander motor 42 is monitored at least based on the current of the expander motor 42 during steady-state operation (S20).

[0096] In S20, a current threshold Th is obtained based on the operating conditions of the expander motor 42 (e.g., motor current signal S1, output frequency information S2, magnitude of the external magnetic field, and input voltage flowing to the inverter 90, etc.) (S21). The measured current value of the expander motor 42 is compared with the obtained current threshold Th (S22). If the measured current value exceeds the current threshold Th (Yes in S22), the comparison unit 70 determines that an abnormal operation of the expander motor 42 has been predicted (S23) and outputs monitoring result data D1 indicating this condition. If the measured current value is below the current threshold Th (No in S22), the comparison unit 70 determines that an abnormal operation of the expander motor 42 has not been predicted (S24) and outputs monitoring result data D1 indicating this condition. Thus, this monitoring method ends.

[0097] In addition, if abnormal operation of the expander motor 42 is predicted, the controller of the cryogenic refrigerator 10 (e.g., the compressor controller 24) can take countermeasures to prevent the occurrence of abnormal operation in advance, such as issuing a warning, reducing the operating frequency of the expander motor 42, or stopping the operation of the cryogenic refrigerator 10.

[0098] The processing unit 100 periodically and repeatedly performs the above monitoring. Since the increase in the drive load of the expander motor 42 is a long-term phenomenon that progresses gradually over a long period, it is practically sufficient to perform this monitoring method only occasionally during the operation of the cryogenic refrigerator 10 (e.g., during steady-state operation). Alternatively, the monitoring method can be performed continuously throughout the operation of the cryogenic refrigerator 10.

[0099] When the cryogenic refrigerator 10 operates continuously for a long period of time, most of the operating time is in steady state. By monitoring during steady-state operation, it is possible to understand the gradual increase in the load torque of the expander motor 42 caused by the deterioration of the components of the cryogenic refrigerator 10 over time.

[0100] As described above, according to the embodiment, the current supplied from the inverter 90 to the expander motor 42 is measured, and the expander motor 42 is monitored at least based on the current of the expander motor 42 in steady-state operation (e.g., the effective value of the current), thereby enabling the prediction or early prevention of abnormal operation or failure of the expander motor 42 caused by long-term operation.

[0101] If the load on the expander motor 42 is allowed to increase unchecked, it will eventually lead to a malfunction of the cryogenic refrigerator 10. In the event of a malfunction, the operation of any cryogenic system utilizing the cryogenic refrigerator 10 (e.g., a superconducting machine or an MRI system) must be stopped until maintenance such as repair or replacement of the cryogenic refrigerator is completed. In the event of a sudden malfunction, the repair time is often relatively long.

[0102] However, according to the implementation method, the expander motor 42 can be monitored, and the monitoring results can be notified to the user of the cryogenic refrigerator 10 or the technician who maintains the cryogenic refrigerator 10. Based on the monitoring results, the impact on the operation of the cryogenic system can be minimized.

[0103] Furthermore, in one embodiment, there are sometimes situations where the output voltage from the inverter 90 (i.e., the input voltage flowing to the expander motor 42) differs from the input voltage flowing to the inverter 90. For example, the inverter 90 may have the function of limiting the output voltage to a specified voltage value (e.g., 200V) when the input voltage exceeds that specified voltage value. However, the inverter 90 may also not have a boost function. In this case, if the input voltage is less than the specified voltage value, the input voltage and output voltage are equal; however, if the input voltage exceeds the specified voltage value, the input voltage and output voltage are different (the output voltage becomes lower than the input voltage). And, as another example, depending on how the inverter 90 controls the motor operating frequency, the input voltage and output voltage may differ. For example, in typical Vf control, even if the input voltage is the specified voltage value, the output voltage may sometimes be lower than that specified voltage value depending on the operating frequency.

[0104] Therefore, as an example of a parameter to be referenced for setting the current threshold, in addition to the motor operating conditions mentioned above, such as the operating frequency (or any of these operating conditions), the output voltage can also be used.

[0105] Figure 7 This is a block diagram of the motor monitoring device according to the embodiment. The monitoring device includes a processing unit 100 configured to monitor the expander motor 42 based on a motor current signal S1 from a current sensor 50. The processing unit 100 can monitor the expander motor 42 during at least steady-state operation of the cryogenic refrigerator 10. The monitoring device may also include a notification mechanism 80 that notifies the monitoring results; the notification mechanism 80 may, for example, include a display 82.

[0106] The processing unit 100 is configured to acquire a current threshold Th based on the operating conditions of the expander motor 42, and compare the current (e.g., the effective value of the current) of the expander motor 42 with the current threshold Th based on the motor current signal S1, thereby monitoring the expander motor 42.

[0107] The processing unit 100 includes a current threshold setting unit 60 and a comparison unit 70. The current threshold setting unit 60 includes an operating frequency / current threshold table 62 and an output voltage / current threshold table 68. The operating frequency / current threshold table 62 establishes a correspondence between multiple current thresholds and multiple values ​​of the operating frequency of the expander motor 42, and the output voltage / current threshold table 68 establishes a correspondence between multiple current thresholds and multiple values ​​of the output voltage from the inverter 90. These current threshold tables are preset and stored in the processing unit 100. These current threshold tables can be appropriately set based on the designer's experience, experiments, or simulations.

[0108] For example, the current threshold setting unit 60 is configured to obtain a current threshold Th corresponding to the operating frequency value based on the value of the operating frequency / current threshold table 62 and the operating frequency of the expander motor 42. The inverter 90 is configured to output output frequency information S2, which represents the value of the output frequency of the inverter 90 (i.e., the operating frequency of the expander motor 42), to the processing unit 100.

[0109] The current threshold setting unit 60 can be configured to obtain a current threshold Th corresponding to the output voltage value based on the output voltage / current threshold table 68 and the value of the output voltage from the inverter 90. Information indicating the value of the output voltage from the inverter 90 can be input from the inverter 90 to the processing unit 100 for use by the current threshold setting unit 60. For example, the inverter 90 can be configured to output an output voltage signal S4 indicating the value of the inverter 90's output voltage (i.e., the input voltage flowing to the expander motor 42) to the processing unit 100, in addition to outputting output frequency information S2.

[0110] Multiple output voltage / current threshold tables 68 can be preset, and these multiple output voltage / current threshold tables 68 can also be associated with values ​​of multiple different operating frequencies. For example, first and second output voltage / current threshold tables 68 can be preset, and the first output voltage / current threshold table 68 can be used when the expander motor 42 is driven at a first operating frequency value (e.g., 70Hz), and the second output voltage / current threshold table 68 can be used when the expander motor 42 is driven at a second operating frequency value (e.g., 60Hz), which is different from the first operating frequency value.

[0111] The comparison unit 70 compares the current (e.g., the effective value of the current) of the expander motor 42 with the acquired current threshold Th based on the motor current signal S1, and generates monitoring result data D1 based on the comparison result. (Compared with reference...) Figure 5Similarly, in the implementation described, the monitoring result data D1 is transmitted to the notification unit 80, and the monitoring result is displayed on the display 82, for example, to notify the user.

[0112] Therefore, by monitoring the expander motor 42 based on the current (e.g., the effective value of the current) of the expander motor 42, it is also possible to predict or prevent abnormal operation or failure of the expander motor 42 caused by long-term operation.

[0113] In the above embodiments, an example of monitoring based on motor current was described, but monitoring can also be performed based on the power consumption of the inverter 90 or the expander motor 42. Such embodiments will be described below.

[0114] Figure 8 This is a graph showing the relationship between the power consumption of inverter 90 and the load duty cycle at multiple operating frequencies. This graph is based on the inventors' measurements. The vertical axis represents the power consumption of inverter 90. Figure 3 Similarly, the horizontal axis represents the load duty cycle of the expander motor 42.

[0115] Depend on Figure 8 It is known that as the load duty cycle increases, the power consumption tends to increase. Therefore, for a certain operating frequency (e.g., 60Hz), the power consumption value when the load duty cycle is less than 100% and sufficiently large (e.g., 90%–98%) can be used as the power consumption threshold. When the power consumption of the inverter 90 (or expander motor 42) exceeds this power consumption threshold, a large load corresponding to that load duty cycle is applied to the expander motor 42. This can be considered as a prediction of abnormal operation of the expander motor 42, thereby enabling the implementation of countermeasures to prevent abnormal operation in advance, such as issuing warnings, reducing the operating frequency, and stopping the operation of the cryogenic refrigerator 10.

[0116] The power consumption depends on the operating frequency of the expander motor 42. For example... Figure 8 As shown, the power consumption values ​​for the same load duty cycle are different when the operating frequency is 50Hz and 60Hz. Therefore, in this embodiment, power consumption thresholds are set for multiple values ​​of the operating frequency of the expander motor 42.

[0117] Compared to the aforementioned monitoring based on motor current, monitoring based on the power consumption of the expander motor 42 has the following advantages: it can reduce the possibility of mispredictions caused by the influence of external magnetic fields. As mentioned above, external magnetic fields sometimes cause increases or decreases in the current flowing through the expander motor 42. External magnetic fields sometimes also cause similar increases or decreases in power consumption. However, according to the inventors' measurements and research, the change in power consumption when the load duty cycle changes by a certain unit amount (e.g., 1%) tends to be greater than the change in motor current when the load duty cycle changes by a certain unit amount. In other words, Figure 8 The slope of the chart is greater than Figure 3 The trend of the slope of the graph. Therefore, the change in apparent load duty cycle corresponding to the change in power consumption caused by an external magnetic field of a certain magnitude tends to be smaller than the change in apparent load duty cycle corresponding to the change in motor current caused by the same external magnetic field. Therefore, in the monitoring of the expander motor 42 based on power consumption, the influence of the external magnetic field can be relatively reduced.

[0118] And, with Figure 3 Compared to the relationship between the motor current value and the load duty cycle shown, as... Figure 8 As shown, the relationship between power consumption and load duty cycle is closer to a straight line. Therefore, it also has the advantage of making it easier to monitor the operation in areas with lower load duty cycles.

[0119] Figure 9 This is a block diagram of a motor monitoring device according to another embodiment. The monitoring device includes a processing unit 100 that monitors the expander motor 42 based on a power consumption signal S5 indicating the power consumption of the inverter 90. The inverter 90 may be configured to output not only output frequency information S2 and output voltage signal S4 to the processing unit 100, but also a power consumption signal S5 indicating the power consumption of the inverter 90 to the processing unit 100. The processing unit 100 monitors the expander motor 42 based on the power consumption signal S5 output from the inverter 90. The monitoring device may also include a notification mechanism 80 that notifies information indicating the monitoring results. The notification mechanism 80 may, for example, include a display 82.

[0120] The processing unit 100 obtains the power consumption threshold Th2 based on the operating conditions of the expander motor 42, and compares the power consumption value of the inverter 90 with the power consumption threshold Th2 based on the power consumption signal S5, thereby monitoring the expander motor 42.

[0121] The processing unit 100 includes a power consumption threshold setting unit 61 and a comparison unit 70. The power consumption threshold setting unit 61 includes an operating frequency / power consumption threshold table 63 and an output voltage / power consumption threshold table 69. The operating frequency / power consumption threshold table 63 establishes a correspondence between multiple power consumption thresholds and multiple values ​​of the operating frequency of the expander motor 42, while the output voltage / power consumption threshold table 69 establishes a correspondence between multiple power consumption thresholds and multiple values ​​of the output voltage from the inverter 90. These power consumption threshold tables are preset and stored in the processing unit 100. These power consumption threshold tables can be appropriately set based on the designer's experience, experiments, or simulations.

[0122] For example, the power consumption threshold setting unit 61 is configured to obtain a power consumption threshold Th2 corresponding to the operating frequency value based on the value of the operating frequency / power consumption threshold table 63 and the operating frequency of the expander motor 42. The inverter 90 is configured to output output frequency information S2, which represents the value of the output frequency of the inverter 90 (i.e., the operating frequency of the expander motor 42), to the processing unit 100.

[0123] The operating frequency / power consumption threshold table 63 can also establish a corresponding power consumption threshold for each of the multiple values ​​of the operating frequency of the expander motor 42. This threshold is defined as the power consumption value of the inverter 90 (or expander motor 42) at that operating frequency when a load torque less than the maximum allowable load torque of the expander motor 42 is applied to the expander motor 42 (i.e., at a specified load duty cycle). The specified load duty cycle can, for example, be selected from a range of 80% or more and less than 100%, or a range of 90% or more and less than 98%.

[0124] Multiple operating frequency / power consumption threshold tables 63 can be preset, and these multiple operating frequency / power consumption threshold tables 63 can also be associated with multiple different load duty cycle values. The power consumption threshold setting unit 61 can also obtain the power consumption threshold Th2 corresponding to the operating frequency value based on the operating frequency / power consumption threshold tables 63 selected from the multiple operating frequency / power consumption threshold tables 63 and the operating frequency value of the expander motor 42.

[0125] The power consumption threshold setting unit 61 can be configured to obtain a power consumption threshold Th2 corresponding to the output voltage value based on the output voltage / power consumption threshold table 69 and the value of the output voltage from the inverter 90. The inverter 90 can be configured to output an output voltage signal S4, representing the value of the inverter 90's output voltage (i.e., the input voltage flowing to the expander motor 42), to the processing unit 100, in addition to outputting the output frequency information S2.

[0126] Multiple output voltage / power consumption threshold tables 69 can be preset, and these multiple output voltage / power consumption threshold tables 69 can also be associated with values ​​of multiple different operating frequencies. For example, first and second output voltage / power consumption threshold tables 69 can be preset, and the first output voltage / power consumption threshold table 69 can be used when the expander motor 42 is driven at a first operating frequency value (e.g., 70Hz), and the second output voltage / power consumption threshold table 69 can be used when the expander motor 42 is driven at a second operating frequency value (e.g., 60Hz), which is different from the first operating frequency value.

[0127] The comparison unit 70 compares the power consumption value of the inverter 90 with the acquired power consumption threshold Th2 based on the power consumption signal S5, and generates monitoring result data D1 based on the comparison result. (Compared with reference...) Figure 5 Similarly, in the implementation described, the monitoring result data D1 is transmitted to the notification unit 80, and the monitoring result is displayed on the display 82, for example, to notify the user.

[0128] Furthermore, the processing unit 100 can perform monitoring of the power-consuming expander motor 42 during at least steady-state operation of the cryogenic refrigerator 10. Figure 5 Similarly, in the illustrated embodiment, the processing unit 100 can obtain information indicating the current operating mode of the cryogenic refrigerator 10 from a controller (e.g., compressor controller 24) or determine the current operating mode based on the measured temperature signal S3 from the temperature sensor 52. The processing unit 100 can monitor the expander motor 42 based on the power consumption signal S5 when the current operating mode is steady-state operation. Alternatively, the processing unit 100 can also monitor the expander motor 42 based on the power consumption signal S5 when the current operating mode is cooling operation.

[0129] The processing unit 100 can also monitor the expander motor 42 based on the power consumption signal S5, which indicates the power consumption of the expander motor 42, thereby replacing the power consumption of the inverter 90. In this case, the processing unit 100 can acquire the current and voltage supplied to the expander motor 42 and calculate the power consumption of the expander motor 42 based on these currents and voltages. The processing unit 100 can also acquire the current of the expander motor 42 based on the motor current signal S1 input from the current sensor 50. The processing unit 100 can also acquire the voltage of the expander motor 42 based on the output voltage signal S4 input from the inverter 90. Alternatively, a voltage sensor can be provided to measure the voltage supplied to the expander motor 42, and the processing unit 100 can acquire the voltage of the expander motor 42 based on the motor voltage signal input from the voltage sensor. The processing unit 100 can compare the power consumption of the expander motor 42 with the acquired power consumption threshold Th2 based on the power consumption signal S5, and generate monitoring result data D1 based on the comparison result.

[0130] Figure 10 This is a flowchart illustrating a monitoring method for an ultra-low temperature refrigerator 10 according to another embodiment. First, as... Figure 10 As shown, during the operation of the cryogenic refrigerator 10 (e.g., during steady-state operation), the power consumption of the inverter 90 (or expander motor 42) is acquired (S30). Furthermore, the expander motor 42 is monitored based on the acquired power consumption (S40).

[0131] In step S40, the power consumption threshold Th2 is obtained based on the operating conditions of the expander motor 42 (e.g., output frequency information S2, output voltage signal S4, etc.) (S41). The obtained power consumption value of the inverter 90 is compared with the power consumption threshold Th2 (S42). If the power consumption value exceeds the power consumption threshold Th2 (Yes in S42), the comparison unit 70 determines that an abnormal operation of the expander motor 42 has been predicted (S43) and outputs monitoring result data D1 indicating this. If the power consumption value is below the power consumption threshold Th2 (No in S42), the comparison unit 70 determines that an abnormal operation of the expander motor 42 has not been predicted (S44) and outputs monitoring result data D1 indicating this. Thus, this monitoring method ends.

[0132] In addition, if abnormal operation of the expander motor 42 is predicted, the controller of the cryogenic refrigerator 10 (e.g., the compressor controller 24) can take countermeasures to prevent abnormal operation in advance, such as issuing a warning, reducing the operating frequency of the expander motor 42, or stopping the operation of the cryogenic refrigerator 10.

[0133] Thus, according to the implementation method, the expander motor 42 is monitored based on the power consumption of the frequency converter 90 (or expander motor 42), thereby enabling the prediction or early prevention of abnormal operation or failure of the expander motor 42 caused by long-term operation.

[0134] 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.

[0135] In the above embodiment, in order to obtain the current threshold based on the operating conditions of the expander motor 42, the processing unit 100 includes three current threshold tables: an operating frequency / current threshold table 62, an external magnetic field / current threshold table 64, and an input voltage / current threshold table 66. However, these three tables are not mandatory. For example, the processing unit 100 may only include the operating frequency / current threshold table 62.

[0136] Alternatively, the processing unit 100 may not include the operating frequency / current threshold table 62. In this case, the processing unit 100 may include an external magnetic field / current threshold table 64 and / or an input voltage / current threshold table 66, wherein the external magnetic field / current threshold table 64 (or the input voltage / current threshold table 66) can be preset to a specific operating frequency for monitoring. In this case, the processing unit 100 can determine whether the expander motor 42 is operating at the specific operating frequency for monitoring based on the output frequency information S2, and compare the current of the expander motor 42 with the current threshold based on the motor current signal S1 obtained during operation at that specific operating frequency, thereby monitoring the expander motor 42.

[0137] Furthermore, the processing unit 100 can be configured to operate the inverter 90 at a monitoring operating frequency to drive the expander motor 42, and to monitor the expander motor 42 by comparing the current of the expander motor 42 with a current threshold based on the motor current signal S1 when the expander motor 42 is driven at the monitoring operating frequency. Therefore, in the comparison of the current of the expander motor 42 with the current threshold, a fixed current threshold corresponding to the monitoring operating frequency can be used. Additionally, in this case, the current threshold can be adjusted according to motor operating conditions such as external magnetic fields.

[0138] In one embodiment, the cryogenic refrigerator 10 can be a single-stage GM refrigerator, or it can be another type of cryogenic refrigerator equipped with an expander motor 42 for actuating the expander 14.

[0139] In one embodiment, the processing unit 100 may not be part of the cryogenic refrigerator 10, but may be part of a cryogenic system (e.g., a superconducting machine or an MRI system) equipped with the cryogenic refrigerator 10.

[0140] The present invention has been described above with reference to specific embodiments and specific statements. However, the embodiments only represent one aspect of the principle and application of the present invention. Without departing from the spirit of the present invention as defined by the technical solution, there may be many variations or configuration changes in the embodiments.

[0141] Industrial availability

[0142] This invention can be applied to the field of cryogenic refrigerators and monitoring methods for cryogenic refrigerators.

[0143] Symbol Explanation

[0144] 10-Cryogenic refrigerator, 14-Expander, 42-Expander motor, 50-Current sensor, 62-Operating frequency / current threshold meter, 64-External magnetic field / current threshold meter, 90-Inverter, 100-Processing unit.

Claims

1. A cryogenic refrigerator capable of performing steady-state operation and cooling operation prior to steady-state operation, characterized in that, have: An expander motor causes the expander of the cryogenic refrigerator to operate; The frequency converter is configured to control the operating frequency of the expander motor, and is capable of driving the expander motor at an operating frequency lower than the operating frequency of the cooling operation during the steady-state operation. A current sensor measures the current supplied from the frequency converter to the expander motor and outputs a motor current signal representing the current. and The processing unit monitors the expander motor based at least on the motor current signal during steady-state operation. The processing unit includes an external magnetic field / current threshold table that establishes a corresponding association between multiple current thresholds and multiple values ​​of the external magnetic field applied to the expander motor. It obtains a current threshold corresponding to the value of the external magnetic field based on the external magnetic field / current threshold table and the value of the external magnetic field applied to the expander motor, and compares the current of the expander motor with the corresponding current threshold based on the motor current signal, thereby monitoring the expander motor.

2. The cryogenic refrigerator according to claim 1, characterized in that, The processing unit obtains a current threshold based on the operating conditions of the expander motor, and compares the current of the expander motor with the current threshold based on the motor current signal, thereby monitoring the expander motor.

3. The cryogenic refrigerator according to claim 1 or 2, characterized in that, The processing unit includes an operating frequency / current threshold table that establishes a corresponding association between multiple current thresholds and multiple values ​​of the operating frequency of the expander motor. It obtains a current threshold corresponding to the value of the operating frequency based on the operating frequency / current threshold table and the value of the operating frequency of the expander motor, and compares the current of the expander motor with the corresponding current threshold based on the motor current signal, thereby monitoring the expander motor.

4. The cryogenic refrigerator according to claim 3, characterized in that, In the operating frequency / current threshold table, the plurality of current thresholds are respectively associated with the plurality of values ​​of the operating frequency of the expander motor in such a way that the current threshold decreases as the operating frequency increases in at least a portion of the range of operating frequencies of the expander motor that can be controlled by the frequency converter.

5. The cryogenic refrigerator according to claim 3 or 4, characterized in that, In the operating frequency / current threshold table, for each of the plurality of values ​​of the operating frequency of the expander motor, the current value of the expander motor at that operating frequency value is established as a current threshold when a load torque less than a specified amount than the maximum allowable load torque in the expander motor is applied to the expander motor.

6. The cryogenic refrigerator according to any one of claims 1 to 5, characterized in that, The processing unit obtains an estimated value of the external magnetic field applied to the expander motor based on the motor current signal, and obtains a current threshold corresponding to the estimated value of the external magnetic field based on the external magnetic field / current threshold table and the estimated value of the external magnetic field applied to the expander motor.

7. The cryogenic refrigerator according to any one of claims 1 to 6, characterized in that, The processing unit includes an input voltage / current threshold table that establishes corresponding associations between multiple current thresholds and multiple values ​​of the input voltage flowing to the frequency converter. It obtains a current threshold corresponding to the value of the input voltage based on the input voltage / current threshold table and the value of the input voltage flowing to the frequency converter, and compares the current of the expander motor with the corresponding current threshold based on the motor current signal, thereby monitoring the expander motor.

8. The cryogenic refrigerator according to any one of claims 1 to 6, characterized in that, The processing unit includes an output voltage / current threshold table that establishes corresponding associations between multiple current thresholds and multiple values ​​of the output voltage from the inverter. It obtains a current threshold corresponding to the value of the output voltage based on the output voltage / current threshold table and the value of the output voltage from the inverter, and compares the current of the expander motor with the corresponding current threshold based on the motor current signal, thereby monitoring the expander motor.

9. A monitoring method for an ultra-low temperature refrigerator, characterized in that, The cryogenic refrigerator is capable of performing steady-state operation and cooling operation prior to steady-state operation, and includes: an expander motor for operating the expander of the cryogenic refrigerator; and a frequency converter configured to control the operating frequency of the expander motor, and capable of driving the expander motor at an operating frequency lower than the operating frequency of the cooling operation during the steady-state operation. The monitoring method includes the following steps: Measure the current supplied from the frequency converter to the expander motor; Based on an external magnetic field / current threshold table that establishes a correspondence between multiple current thresholds and multiple values ​​of the external magnetic field applied to the expander motor, and the values ​​of the external magnetic field applied to the expander motor, a current threshold corresponding to the value of the external magnetic field is obtained. The expander motor is monitored at least based on its current during steady-state operation by comparing the current of the expander motor with the corresponding current threshold.

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