Control system and method for an ultra-low temperature refrigerator

Abstract

The application discloses a control system and method of an ultralow-temperature refrigerator, which comprises a compressor, an electric control system and a refrigerator; the compressor is provided with a low-pressure sensor, a high-pressure sensor and a temperature sensor for collecting ambient temperature; the electric control system comprises a control system, a power supply, a frequency converter and an interlocking mechanism; one end of the control system is connected with the low-pressure sensor, the high-pressure sensor and the temperature sensor respectively, and the other end is connected with the power supply; one end of the interlocking mechanism is connected with the power supply and the frequency converter respectively, and the other end is connected with a cold head of the refrigerator, so that only one of the power supply and the frequency converter is connected with the cold head of the refrigerator; the control system is used for controlling the output of the frequency converter and the power supply after processing signals. The application adopts the mode that the frequency converter steplessly controls the rotating speed of the cold head motor in the starting stage and the motor fixed-frequency controls the rotating speed of the cold head motor in the ultralow-temperature stage, so that the starting time of the refrigerator is shortened, the electromagnetic interference of the frequency converter on the equipment in the ultralow-temperature condition is avoided, and the performance of the ultralow-temperature refrigerator is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a control system and method, in particular to a control system and method of a super-low temperature refrigerator. BACKGROUND

[0002] The super-low temperature refrigerator is widely used as a low-temperature cold source in the fields of superconducting magnet cooling, deep low-temperature physical property detection, etc. The working temperature of the super-low temperature refrigerator is generally below 70K, and mainly concentrates on 4K or below. The cooled equipment needs to be cooled from room temperature to extremely low temperature before use. The cooling process is the start-up stage of the equipment, and it is generally required that the process time be as short as possible.

[0003] In the cooling process of the conventional super-low temperature refrigeration system, the control system controls the motor of the refrigerator to operate at a constant frequency. During the cooling process, the exhaust capacity of the compressor is greater than the gas capacity required by the refrigerator, which causes the high pressure of the compressor to increase, the low pressure to decrease, and the pressure difference to increase. The high pressure of the compressor has a limit value during operation, and therefore a one-way valve with a set pressure difference is provided in the compressor. When the pressure difference is greater than the set pressure difference of the one-way valve, part of the exhaust gas of the compressor passes through the one-way valve instead of the refrigerator, which reduces the high pressure of the exhaust gas of the compressor and causes part of the exhaust capacity of the compressor to be lost during the cooling process, thereby reducing the efficiency of the refrigerator.

[0004] Another way is to detect the high-low pressure difference or the high pressure, and control the electromagnetic valve connected to the high-low pressure pipeline in the compressor. When the detected pressure difference or high pressure is greater than the target value, the electromagnetic valve is opened, part of the exhaust gas of the compressor passes through the electromagnetic valve instead of the refrigerator, which causes part of the exhaust capacity of the compressor to be lost during the cooling process, thereby reducing the efficiency of the refrigerator.

[0005] The prior art discloses a method for controlling the frequency of the compressor to adjust the exhaust capacity of the compressor and adjusting the control system of the refrigeration system, and also discloses a method for reducing the refrigeration system by comparing the high-low pressure difference with the set target value to control the operating frequency of the cold head motor. During the cooling process, the cold head operates at a constant frequency, and only the operating frequency of the compressor can be reduced to reduce the exhaust capacity of the compressor. This method can reduce the energy consumption of the system, but cannot shorten the cooling time of the system. The high pressure difference control cannot effectively control the upper limit of the high pressure of the compressor, and is prone to cause the compressor to operate at an overpressure, thereby reducing the reliability of the system.

[0006] The main factors limiting the operating pressure of the system during the cooling process of the super-low temperature refrigeration system are the operating high pressure limit of the compressor and the small gas capacity of the refrigerator in the high temperature zone, and therefore it is necessary to control the operating high pressure and increase the operating frequency of the cold head to increase the gas capacity of the cold head, thereby improving the refrigeration capacity. SUMMARY

[0007] The application aims to provide a control system of an ultra-low temperature refrigerator with increased refrigeration capacity in a cooling process.

[0008] The second object of the application is to provide a control method of the control system of the ultra-low temperature refrigerator without electromagnetic interference in a stable operation condition.

[0009] The control system of the ultra-low temperature refrigerator comprises a compressor, an electric control system and a refrigerator, wherein the compressor is provided with a low-pressure sensor, a high-pressure sensor and a temperature sensor for collecting ambient temperature; the electric control system comprises a control system, a power supply, a frequency converter and an interlocking mechanism; one end of the control system is connected with the low-pressure sensor, the high-pressure sensor and the temperature sensor respectively, and the other end is connected with the power supply; one end of the interlocking mechanism is connected with the power supply and the frequency converter respectively, and the other end is connected with a cold head of the refrigerator, so that only one of the power supply and the frequency converter is connected with the cold head of the refrigerator; the control system is used for processing signals and controlling the output of the frequency converter and the power supply.

[0010] The compressor comprises a compression package, a solenoid valve, a check valve, a safety valve, a low-pressure sensor, a high-pressure sensor, a compressor low-pressure pipe, a compressor high-pressure pipe, a compressor high-pressure joint and a compressor low-pressure joint; the high-pressure sensor and the low-pressure sensor are used for collecting the pressure of the outlet pipe and the inlet pipe of the compressor respectively; one end of the low-pressure connecting pipe is connected with one end of the compressor low-pressure joint, and the other end of the compressor low-pressure joint is connected with one end of the compressor low-pressure pipe; the other end of the compressor low-pressure pipe is sequentially connected with one end of the low-pressure sensor, one end of the check valve, one end of the solenoid valve and one end of the compression package; one end of the compressor high-pressure pipe is sequentially connected with the other end of the compression package, the other end of the solenoid valve, the other end of the check valve, the safety valve and one end of the high-pressure sensor; the other end of the compressor high-pressure pipe is connected with one end of the compressor high-pressure joint; and the other end of the compressor high-pressure joint is connected with one end of the high-pressure connecting pipe.

[0011] The refrigeration machine is provided with a cold head power supply interface, a cold head low-pressure connector, a cold head high-pressure connector, a cold head cover, a cold head motor, a rotary valve, a gas distribution valve, a piston driving connecting rod, a first-stage piston, a second-stage piston, a first-stage cylinder, a second-stage cylinder, a first flange and a second flange.

[0012] The application utilizes the control method of the control system of the ultra-low temperature refrigeration machine to control the motor rotating speed and the refrigeration capacity of the refrigeration machine by determining the pressure of the high-pressure sensor and the revised pressure.

[0013] The method comprises the following steps:

[0014] (A) revising the target pressure value of the compressor outlet according to the data collected by the high-pressure sensor and the temperature sensor;

[0015] (B) the control system receives the pressure value of the high-pressure sensor and the ambient temperature of the temperature sensor, and calculates the upper and lower limits of the current target pressure in real time; when the pressure of the high-pressure sensor is greater than the upper limit value of the target pressure, the system is in a cooling state, the refrigeration capacity of the refrigeration machine is lower than the outlet pressure of the compressor, the frequency converter is started to increase the rotating speed of the cold head motor, and the refrigeration capacity of the refrigeration machine is increased;

[0016] (C) when the pressure of the high-pressure sensor is lower than the lower limit value of the target pressure, the starting stage is ended, the working medium is in an ultra-low temperature state, the outlet pressure of the compressor is reduced, and the cold head motor can be switched to the power supply fixed-frequency regulation; the switching of the power supply and the frequency converter is realized by using an interlocking mechanism; the safety and reliability of the electric control system can be improved, and the equipment can be protected from improper use or operation errors.

[0017] In step (A), the ambient temperature collected by the temperature sensor is used to revise the target pressure, and the revision method is based on the ideal gas state equation PV=NRT; the relationship between the revised pressure and the actual pressure is as follows:

[0018]

[0019] In the formula, P 修正P is the critical value of the actual outlet pressure of the compressor, MPa; T is the temperature collected by the temperature sensor, ℃, the ambient temperature corresponding to the air-cooled compressor, and the water inlet temperature corresponding to the water-cooled compressor; P0 is the critical value of the theoretical outlet pressure of the compressor, MPa; and T0 is the temperature corresponding to the critical value of the theoretical outlet pressure, ℃.

[0020] In step (B), the frequency setting of the frequency converter adopts a stepless control strategy, the output PWM signal frequency is changed smoothly according to the relationship between the current pressure and the critical upper limit pressure, and the greater the pressure difference, the higher the motor speed of the cold head.

[0021] In step (B), the frequency setting of the frequency converter adopts a stepless control strategy, the output PWM signal frequency is changed smoothly according to the relationship between the current pressure and the critical upper limit pressure, and the greater the pressure difference, the higher the motor speed of the cold head.

[0022] In step (B), the frequency setting of the frequency converter adopts a stepless control strategy, the output PWM signal frequency is changed smoothly according to the relationship between the current pressure and the critical upper limit pressure, and the greater the pressure difference, the higher the motor speed of the cold head.

[0023] Advantages: Compared with the prior art, the present application has the following remarkable effects:

[0024] (1) The present application is aimed at the problem of long equipment startup time and low efficiency of the refrigeration machine in the conventional equipment cooling process, and adopts the mode of stepless control of the motor speed of the cold head by the frequency converter in the startup stage and the mode of fixed-frequency control of the motor speed of the cold head in the ultra-low temperature stage, so as to shorten the cooling time of the cooled product, avoid the electromagnetic interference of the frequency converter on the equipment in the ultra-low temperature condition, and improve the performance of the ultra-low temperature refrigeration machine.

[0025] (2) The present application controls the refrigeration capacity change of the high-temperature zone of the refrigeration machine based on the high-pressure of the compressor, reduces the gas amount flowing into the bypass of the compressor, increases the gas amount flowing into the refrigeration machine, improves the efficiency of the refrigeration system in the cooling process, and shortens the refrigeration time.

[0026] (3) On the basis of the frequency converter control, the stepless control of the PWM frequency output by the control system further improves the refrigeration efficiency, the interlocking mechanism connects the power supply and the frequency converter, improves the safety and reliability of the electric control system, and protects the equipment from the influence of improper use or operation errors. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The control system structure schematic diagram of the ultra-low temperature refrigerator of the present application;

[0028] Figure 2 The control strategy flow schematic diagram of the present application;

[0029] Figure 3 The point line graph of the compressor outlet pressure and pressure fluctuation changing with refrigeration time in the prior art. DETAILED DESCRIPTION

[0030] The present application will be described in further detail below.

[0031] Referring to Figure 1 The present application provides a control system of an ultra-low temperature refrigerator, comprising a compressor 1, an electric control system 2 and a refrigerator 3.

[0032] The compressor 1 comprises a compression package 6, a solenoid valve 7, a check valve 8, a safety valve 9, a low pressure sensor 10, a high pressure sensor 11, a compressor low pressure pipe 12, a compressor high pressure pipe 13, a temperature sensor 34, a compressor high pressure joint 15 and a compressor low pressure joint 14. The compression package 6 is used for pressurizing helium. The check valve 8 is used for maintaining the pressure difference between the inlet and outlet of the compressor 1. The safety valve 9 is used for protecting the equipment safety. The solenoid valve 7 is used for adjusting the pressure difference between the inlet and outlet. The temperature sensor 34 is used for collecting the ambient temperature. The low pressure sensor 10 and the high pressure sensor 11 are respectively used for collecting the pressure of the inlet pipe and the outlet pipe of the compressor 1. The inlet pipe is connected with the low pressure connecting pipe 4, and the outlet pipe is connected with the high pressure connecting pipe 5.

[0033] One end of the low pressure connecting pipe 4 is connected with one end of the compressor low pressure joint 14, and the other end of the compressor low pressure joint 14 is connected with one end of the compressor low pressure pipe 12. The other end of the compressor low pressure pipe 12 is sequentially connected with one end of the low pressure sensor 10, one end of the check valve 8, one end of the solenoid valve 7 and one end of the compression package 6. One end of the compressor high pressure pipe 13 is sequentially connected with the other end of the compression package 6, the other end of the solenoid valve 7, the other end of the check valve 8, the safety valve 9 and one end of the high pressure sensor 11. The other end of the compressor high pressure pipe 13 is connected with one end of the compressor high pressure joint 15. The other end of the compressor high pressure joint 15 is connected with one end of the high pressure connecting pipe 5.

[0034] The electric control system 2 comprises a control system 16, a power supply 17, a frequency converter 33 and an interlocking mechanism 35; the control system 16 controls the output of the frequency converter 33 and the power supply 17 after processing signals; the interlocking mechanism 35 is used for protecting the safety of the electric control system; one end of the temperature sensor 34, one end of the high-pressure sensor 11 and one end of the low-pressure sensor 10 are connected with one end of the control system; one end of the control system 16 is connected with one end of the power supply 17; one end of the power supply 17 is connected with one end of the frequency converter 33; one end of the interlocking mechanism 35 is connected with the other end of the power supply 17 and the other end of the frequency converter 33; the other end of the interlocking mechanism 35 is connected with one end of the power supply 17.

[0035] The refrigerator 3 is provided with a cold head power supply interface 18, a cold head low-pressure connector 19, a cold head high-pressure connector 20, a cold head cover 23, a cold head motor 21, a rotary valve 22, a gas distribution valve 24, a piston driving connecting rod 25, a first-stage piston 26, a second-stage piston 29, a first-stage cylinder 27, a second-stage cylinder 30, a first flange 28 and a second flange 31; the cold head power supply interface 18 is connected with the other end of the power supply wire 32; the cold head low-pressure connector 19 is connected with the other end of the low-pressure connecting pipe 4; the cold head high-pressure connector 20 is connected with the other end of the high-pressure connecting pipe 5; the cold head cover 23 serves as the shell of the refrigerator; the cold head motor 21 is used for changing the rotating speed of the rotary valve 22; the rotary valve 22 is used for driving the gas distribution valve 24 and the piston driving connecting rod 25 to rotate; the gas distribution valve 24 and the piston driving connecting rod 25 are coupled and used for changing the refrigerating capacity of the refrigerator 3; the first-stage cylinder 27 contains the first-stage piston 26; one end of the first flange 28 is connected with one end of the first-stage piston 26; one end of the first flange 28 is connected with one end of the second-stage cylinder 30; the second-stage cylinder 30 contains the second-stage piston 29; the other end of the second flange 31 is used for transmitting the refrigerating capacity.

[0036] As shown in Figure 2 , the application discloses a control method of an ultra-low temperature refrigerator; the rotating speed of the motor 21 is controlled by judging the pressure of the high-pressure sensor 11 and the revised pressure, and then the refrigerating capacity of the refrigerator 3 is controlled; the method specifically comprises the following steps:

[0037] Step 1: arranging the high-pressure sensor 11, the low-pressure sensor 10 and the temperature sensor 34 in the compressor 1; according to the data collected by the high-pressure sensor 11 and the temperature sensor 34, the target pressure value of the outlet of the compressor 1 is revised; as shown in Figure 3 , the figure is the test figure of the bare machine of the refrigerator; as can be known from Figure 3 , the outlet pressure of the compressor is the largest in the starting state; with the decrease of the temperature of the refrigerator 3 and the increase of the density, the pressure of the system cycle is reduced, and the outlet pressure of the compressor is gradually reduced to stable, Figure 3The error bar represents the fluctuation of the compressor 1 outlet temperature, and the upper and lower limits of the target pressure are set according to the fluctuation characteristics of the compressor 1 outlet pressure and experimental data.

[0038] In step 2, the control system 16 receives the pressure value of the high-pressure sensor 11 and the ambient temperature of the temperature sensor 34, and calculates the upper and lower limits of the current target pressure in real time. When the pressure of the high-pressure sensor 11 is greater than the upper limit of the target pressure, the system is in a cooling state, and the refrigeration capacity of the refrigerator 3 is lower than the outlet pressure of the compressor 1. The frequency converter 33 is enabled to increase the speed of the cold head motor 21 and improve the refrigeration capacity of the refrigerator 3. The frequency setting of the frequency converter 33 adopts a stepless control strategy, which changes the output PWM signal frequency according to the relationship between the current pressure and the critical upper limit pressure. The greater the pressure difference, the higher the speed of the cold head motor 21.

[0039] In step 3, when the pressure of the high-pressure sensor 11 is lower than the lower limit of the target pressure, the starting stage ends, and the working medium is in a super-low temperature state. The outlet pressure of the compressor 1 is reduced, and the cold head motor 21 can be switched to a fixed frequency regulation power supply 17. An interlocking mechanism 35 is used to switch the power supply 17 and the frequency converter 33. One end of the interlocking mechanism 35 is connected to the power supply 17 and the frequency converter 33, respectively, and the other end is connected to the cold head motor 21 through the power supply wiring 32. This improves the safety and reliability of the electric control system 2 and protects the equipment from improper use or operation errors.

[0040] The temperature sensor 34 revises the target pressure based on the collected ambient temperature according to the ideal gas state equation PV = NRT. The relationship between the revised pressure and the actual pressure is as follows:

[0041]

[0042] In the formula, P 修正 is the critical value of the actual outlet pressure of the compressor 1, MPa; T is the ambient temperature collected by the temperature sensor 34, ℃; P0 is the critical value of the theoretical outlet pressure of the compressor 1, MPa; and T0 is the ambient temperature corresponding to the critical value of the theoretical outlet pressure, ℃.

[0043] By correcting the pressure, a more accurate critical pressure value can be obtained.

[0044] The electric control system 2 adopts two kinds of motor speed control strategies of frequency converter 33 and power supply 17. When the outlet pressure of compressor 1 is higher than the upper limit critical value of target pressure, the cold head motor 21 is driven by the frequency converter 33 to increase the speed of the cold head motor 21, so as to increase the speed of the rotary valve 22 and the crank mechanism of the piston 25, increase the refrigeration capacity of the refrigerator, and thus match the outlet pressure of the compressor 1. When the outlet pressure of the compressor 1 is lower than the lower limit critical value of the target pressure, the refrigerator 3 is in the super-low temperature state, and the signal generated by the frequency converter 33 will produce certain electromagnetic interference, so the power supply 17 can be switched to drive the cold head motor 21 at a constant frequency.

[0045] The frequency converter 33 of the electric control system 2 adopts a stepless control strategy. Since the outlet pressure of the compressor 1 is a fluctuating value, Pmax and Pmin are respectively taken as the upper limit and lower limit of the actual outlet pressure critical value. When the pressure is higher than Pmax, the frequency converter 33 is used to increase the speed of the compressor 1. When the pressure is lower than Pmin, the power supply 17 is used to drive the cold head motor 21 at a constant frequency. In this process, the motor speed is steplessly controlled according to the current pressure within the range of Pmax and Pmin.

[0046] The electric control system 2 uses an interlocking mechanism 35. One end of the interlocking mechanism 35 is respectively connected with the power supply 17 and the frequency converter 33, which can ensure that before any one of the two contactors is turned on, the other contactor must be in a power-off release state, thereby ensuring the safety of the electric control system 2.

Claims

1. A control method of a control system of a super-low-temperature refrigerator, characterized by, The high pressure sensor (11) is used to control the speed of the cold head motor (21) and the refrigeration capacity of the refrigerator (3) by determining the pressure and the revised pressure; including the following steps: A. According to the data collected by the high pressure sensor (11) and the temperature sensor (34), the target pressure value of the compressor (1) outlet is corrected; In step A, the target pressure is revised by the ambient temperature collected by the temperature sensor (34); the relationship between the revised pressure and the actual pressure is as follows: ； In the formula, P 修正 Pcrit is the critical value of the actual outlet pressure of the compressor (1), MPa; T T is the ambient temperature collected by the temperature sensor (34) for the air cooling system, or the cooling water temperature collected by the temperature sensor (34) for the water cooling system, ℃; P Pcrit0 is the critical value of the theoretical outlet pressure of the compressor (1), MPa; T T0 is the temperature corresponding to the critical value of the theoretical outlet pressure, ℃. B. The control system (16) receives the pressure value of the high pressure sensor (11) and the ambient temperature of the temperature sensor (34), and calculates the upper and lower limits of the current target pressure in real time. When the pressure of the high pressure sensor (11) is greater than the upper limit value of the target pressure, the system is in the cooling state, the refrigeration capacity of the refrigerator (3) is lower than the outlet pressure of the compressor (1), and the frequency converter (33) is started to increase the speed of the cold head motor (21) and improve the refrigeration capacity of the refrigerator (3); C. When the pressure of the high pressure sensor (11) is lower than the lower limit value of the target pressure, the starting stage is ended, the working medium is in the super low temperature state, the outlet pressure of the compressor (1) is reduced, and the power supply (17) is switched to the frequency conversion regulation of the cold head motor (21); the interlocking mechanism (35) is used to switch the power supply (17) and the frequency converter (33); The control system of the super low temperature refrigerator, comprising a compressor (1), an electric control system (2) and a refrigerator (3); the compressor (1) is provided with a low pressure sensor (10), a high pressure sensor (11) and a temperature sensor (34) for collecting ambient temperature; the electric control system (2) includes a control system (16), a power supply (17), a frequency converter (33) and an interlocking mechanism (35); one end of the control system is connected with the low pressure sensor (10), the high pressure sensor (11) and the temperature sensor, respectively, and the other end is connected with the power supply (17); one end of the interlocking mechanism (35) is connected with the power supply (17) and the frequency converter (33), respectively, and the other end is connected with the cold head of the refrigerator (3), so that only one of the power supply and the frequency converter is connected with the cold head of the refrigerator (3); the control system (16) is used to process the signal and control the output of the frequency converter (33) and the power supply (17); The compressor (1) includes a compression package (6), a solenoid valve (7), a check valve (8), a safety valve (9), a low pressure sensor (10), a high pressure sensor (11), a compressor low pressure pipe (12), a compressor high pressure pipe (13), a compressor high pressure joint (15), and a compressor low pressure joint (14); the high pressure sensor (11) is used to collect the pressure of the outlet pipeline of the compressor (1), and the low pressure sensor (10) is used to collect the pressure of the inlet pipeline of the compressor (1); one end of the low pressure connecting pipe (4) is connected with one end of the compressor low pressure joint (14), and the other end of the compressor low pressure joint (14) is connected with one end of the compressor low pressure pipe (12); the other end of the compressor low pressure pipe (12) is sequentially connected with one end of the low pressure sensor (10), one end of the check valve (8), one end of the solenoid valve (7), and one end of the compression package (6); one end of the compressor high pressure pipe (13) is sequentially connected with the other end of the compression package (6), the other end of the solenoid valve (7), the other end of the check valve (8), the safety valve (9), and one end of the high pressure sensor (11); the other end of the compressor high pressure pipe (13) is connected with one end of the compressor high pressure joint (15); and the other end of the compressor high pressure joint (15) is connected with one end of the high pressure connecting pipe (5); The refrigeration machine (3) is provided with a cold head power supply interface (18), a cold head low pressure joint (19), a cold head high pressure joint (20), a cold head cover (23), a cold head motor (21), a rotary valve (22), a gas distribution valve (24), a piston driving connecting rod (25), a first stage piston (26), a second stage piston (29), a first stage cylinder (27), a second stage cylinder (30), a first flange (28), and a second flange (31); the cold head power supply interface (18) is connected with the other end of the power supply (17); the cold head low pressure joint (19) is connected with the other end of the low pressure connecting pipe (4); the cold head high pressure joint (20) is connected with the other end of the high pressure connecting pipe (5); the cold head motor (21) is used to change the rotating speed of the rotary valve (22); the rotary valve (22) is used to drive the gas distribution valve (24) and the piston driving connecting rod (25) to rotate; the gas distribution valve (24) and the piston driving connecting rod (25) are coupled to change the refrigeration capacity of the refrigeration machine (3); the first stage cylinder (27) contains the first stage piston (26), one end of the first flange (28) is connected with one end of the first stage piston (26); one end of the first flange (28) is connected with one end of the second stage cylinder (30); the second stage cylinder (30) contains the second stage piston (29), and the other end of the second flange (31) is used to transmit the refrigeration capacity.

2. The control method according to claim 1, characterized by, In step B, the frequency of the frequency converter (33) adopts a stepless control strategy, and the output PWM signal frequency is changed smoothly according to the relationship between the current pressure and the critical upper limit pressure difference; the greater the pressure difference, the higher the rotating speed of the cold head motor (21).

3. The control method according to claim 2, characterized by, In step B, the stepless control strategy process is: taking Pmax and Pmin as the upper and lower limits of the actual outlet pressure critical value of the compressor (1) respectively, when the pressure is higher than Pmax, the frequency converter (33) is used to increase the rotating speed of the compressor (1), when the pressure is lower than Pmin, the power supply (17) is used to drive the motor (21) of the cold head at a constant frequency.

4. The control method according to claim 1, characterized by, In step B, the electric control system (2) adopts two kinds of motor rotating speed control strategies of the frequency converter (33) and the power supply (17): when the outlet pressure of the compressor (1) is higher than the upper limit critical value of the target pressure, the cold head motor (21) is driven by the frequency converter (33), the rotating speed of the cold head motor (21) is increased, the rotating speed of the rotary valve (22) and the piston driving connecting rod (25) crank mechanism is increased, the refrigeration capacity of the supercooling refrigerator is increased, so as to match the outlet pressure of the compressor (1); when the outlet pressure of the compressor (1) is lower than the lower limit critical value of the target pressure, at this time, the supercooling refrigerator (3) is in a superlow temperature state, the signal generated by the frequency converter (33) will produce certain electromagnetic interference, so the power supply (17) is switched to drive the cold head motor (21) at a constant frequency.

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