A Temperature Control Method for a Cooling System of a High-Temperature Superconducting Cable

Abstract

The present invention discloses a temperature control method for a cooling system of a high-temperature superconducting cable. For the existing temperature control methods, the regulation of the temperature of the coolant liquid nitrogen is relatively lagging, unable to respond promptly to the change of the system's heat load, and during the regulation process, the temperature change range is large, the stable period is short, and seriously, the temperature of the coolant liquid nitrogen will reach its vaporization temperature. The technical solution adopted by the present invention is that the circulating liquid nitrogen temperature of the cooling system adopts an adjustment method mainly based on the cable energization current value and supplemented by the liquid nitrogen temperature value at the cable outlet. This adjustment method is completed by a current temperature control unit, a temperature difference control unit, a cooling capacity adjustment unit, and a command output module. The present invention adopts a mixed adjustment method mainly based on the cable energization current value and supplemented by the liquid nitrogen temperature value at the cable outlet, which increases the timeliness of the temperature adjustment of the cooling system, reduces the fluctuation of the cooling system temperature with the change of the energization current, shortens the temperature adjustment time, and increases the stability of the system.

Description

Technical Field

[0001] The present invention belongs to the field of high-temperature superconducting cables, and particularly relates to a temperature control method for a cooling system of a high-temperature superconducting cable. Background Art

[0002] The conductive layer of high-temperature superconducting cables mainly uses tapes such as Bi2223, YBCO, and MgBZ. These materials can achieve superconducting properties within the range of liquid nitrogen, with the resistivity disappearing and almost lossless power transmission being achievable. At normal pressure, the vaporization temperature of liquid nitrogen is 77.36K, and the triple-point temperature is 63.15K. Therefore, the temperature of the cooling system in a high-temperature superconducting cable power transmission system is usually set at 70K - 71K at the inlet and 75K - 76K at the outlet to ensure that the cooling medium is in the liquid nitrogen state. If the temperature of the cooling system is too low, the power consumption of the refrigerator will increase; if the temperature is too high, a gas-liquid two-phase flow will form, affecting the cooling effect and, in severe cases, causing the superconducting material to lose superconductivity.

[0003] The cooling system of high-temperature superconducting cables often uses the temperature of the coolant liquid nitrogen at the outlet of the cable constant-temperature pipe as the control value. When the actual temperature deviates from the set value, the power of the refrigerator, the flow rate of the liquid nitrogen pump, and the output of the vacuum machine are adjusted through the deviation between the actual temperature and the target temperature (i.e., the set value), thereby adjusting the temperature of the coolant liquid nitrogen. This temperature control method has a relatively large lag in adjusting the temperature of the coolant liquid nitrogen, cannot respond in a timely manner to the change in the system's heat load, and during the adjustment process, the temperature changes significantly, with a short stable period. In severe cases, the temperature of the coolant liquid nitrogen will reach its vaporization temperature. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art, and provide a temperature control method for a cooling system of a high-temperature superconducting cable. According to the current passing through the cable, the required refrigerating capacity is obtained. The main adjustment methods are the power of the refrigerator, the flow rate of the liquid nitrogen pump, and the output of the vacuum machine, and the temperature of the coolant liquid nitrogen at the outlet of the cable is used as an auxiliary adjustment method to respond in a timely manner to the change in the system's heat load caused by the change in the power transmission current of the high-temperature superconducting cable, so as to reduce the large fluctuations in the liquid nitrogen temperature during the adjustment process, thereby increasing the stability of the cooling system.

[0005] Therefore, the technical solution adopted by the present invention is as follows: A temperature control method for a cooling system of a high-temperature superconducting cable. The temperature of the circulating liquid nitrogen in the cooling system is adjusted by taking the value of the current passing through the cable as the main factor and the temperature value of the liquid nitrogen at the outlet of the cable as the auxiliary factor. This adjustment method is completed by a current temperature control unit, a temperature difference control unit, a refrigerating capacity adjustment unit, and a command output module;

[0006] The said current temperature control unit: inputs the refrigerating capacity Q0 required to maintain the temperature of the circulating liquid nitrogen when not powered on, receives the real-time current data from the monitoring system, converts the real-time current data into the additional refrigerating capacity ΔQ required for the high-temperature superconducting cable cooling system under this current, and outputs it to the refrigerating capacity adjustment unit;

[0007] The temperature difference control unit is input with the control target value T0 and upper limit value T of the liquid nitrogen temperature at the outlet of the high-temperature superconducting cable. h Receive the real-time temperature T signal of liquid nitrogen at the cable outlet from the monitoring system. When the deviation between the real-time temperature T signal and the control target value T0 is greater than 2K, an alarm signal is output, and the deviation instruction S% is manually input according to the temperature difference (T-T0) and output to the cooling capacity adjustment unit for auxiliary adjustment. When the real-time temperature T is greater than the control temperature upper limit T h When an alarm occurs, the alarm signal is output and sent directly to the command output module;

[0008] The cooling capacity adjustment unit: input the rated power of the refrigerator P e , Liquid nitrogen pump rated flow L e , Vacuum machine rated output W e and the refrigerator power P0, liquid nitrogen pump flow L0, and vacuum machine output W0 when the circulating liquid nitrogen temperature is maintained when the high-temperature superconducting cable is not powered; receiving the comprehensive input ΔQ (1+S%) from the current temperature control unit and the temperature difference control unit, and converting this comprehensive input ΔQ (1+S%) into the refrigerator power ΔP, liquid nitrogen pump flow ΔL, and vacuum machine output ΔW that should be increased, and then outputting them to the instruction output module;

[0009] The command output module receives signals from the cooling capacity adjustment unit and the temperature difference control unit. When only the signal from the cooling capacity adjustment unit is received, the adjustment rate v0 is set and the command is sent to the refrigerator, the liquid nitrogen pump and the vacuum machine, and the refrigerator power is gradually adjusted to P0+ΔP, the liquid nitrogen pump flow is adjusted to L0+ΔL, and the vacuum machine output is adjusted to W0+ΔW; when the signal from the temperature difference control unit is received, the signal from the cooling capacity adjustment unit is bypassed, and a manual control interface is directly popped up to manually control the refrigerator power, liquid nitrogen pump flow, vacuum machine output and disconnection of the high-temperature superconducting circuit, and the command is sent to the refrigerator, the liquid nitrogen pump and the vacuum machine.

[0010] Furthermore, the cooling capacity adjustment unit includes a third setting module, a calculation module and a second judgment module; the rated power P of the refrigerator is input through the third setting module. e , Liquid nitrogen pump rated flow L e , Vacuum machine rated output W e and the refrigerator power P0, liquid nitrogen pump flow L0, and vacuum machine output W0 when the circulating liquid nitrogen temperature is maintained when the high-temperature superconducting cable is not powered; the residual cooling capacity adjustment margins Q1, Q2, and Q3 of the refrigerator, liquid nitrogen pump, and vacuum machine are calculated by the calculation module; the judgment module receives the comprehensive input ΔQ (1+S%) from the current temperature control unit and the temperature difference control unit and the output parameters Q1, Q2, and Q3 of the calculation module, and enters the hierarchical adjustment.

[0011] Furthermore, the cooling capacity adjustment margin Q1 of the refrigerator is calculated by (P e - P0) × COP, where COP is the energy efficiency ratio of the refrigerant; the cooling capacity adjustment margin Q2 of the liquid nitrogen pump is calculated by (L e - L0) × ΔT × C P , where ΔT is the temperature difference of liquid nitrogen at the inlet and outlet of the cable, and C P is the average specific heat of coolant liquid nitrogen; the remaining cooling capacity adjustment margin Q3 of the vacuum machine is calculated by G LN2 × r n2 × ρ, where ρ is the density of coolant liquid nitrogen, G LN2 is the consumed liquid nitrogen volume, r n2 is the latent heat of vaporization of liquid nitrogen, G LN2 and r n2 are related to the pumping speed of the vacuum machine, and the corresponding relationship can be obtained during the system debugging period.

[0012] Furthermore, the cooling capacity adjustment unit adopts a hierarchical adjustment method: when ΔQ(1 + S%) ≤ Q1, adjust the power of the refrigerator; when Q1 < ΔQ(1 + S%) ≤ Q1 + Q2, adjust the power of the refrigerator to the rated value and then adjust the flow rate of the liquid nitrogen pump; when Q1 + Q2 < ΔQ(1 + S%) ≤ Q1 + Q2 + Q3, adjust the power of the refrigerator and the flow rate of the nitrogen pump to the rated value, and then adjust the output of the vacuum machine for vacuum evaporation refrigeration; when ΔQ > Q1 + Q2 + Q3, adjust the power of the refrigerator, the flow rate of the liquid nitrogen pump, and the output of the vacuum machine to the rated value and output an alarm signal.

[0013] Furthermore, the hierarchical adjustment method selects the priority according to the energy consumption levels of the refrigerator and the liquid nitrogen pump; the vacuum machine adjusts the pressure and temperature in the subcooler by adjusting the pumping volume, but the consumed liquid nitrogen volume is large and it needs to be supplemented with liquid nitrogen in a linked manner, and the adjustment priority is set to the lowest.

[0014] Furthermore, the adjustment method of the cooling capacity is determined by the high-temperature superconducting cable cooling system: the cooling capacity of the closed cooling system refrigerated by the refrigerator is adjusted by the refrigerator and the liquid nitrogen pump; the cooling capacity of the open cooling system refrigerated by vacuum evaporation is adjusted by the vacuum machine and the liquid nitrogen pump; the cooling capacity of the hybrid cooling system is adjusted by the refrigerator, the liquid nitrogen pump, and the vacuum machine.

[0015] Furthermore, in the current temperature control unit, the real-time current data is converted into the additional cooling capacity ΔQ required by the high-temperature superconducting cable cooling system at this current according to the relationship between the additional cooling capacity and the change of the cable energizing current.

[0016] Furthermore, the relationship between the additional cooling capacity ΔQ and the cable energizing current is obtained during the commissioning or test stage of the high-temperature superconducting cable cooling system and is represented by a fitting formula or curve.

[0017] Further, according to the requirements of control accuracy, the deviation determination value between the real-time temperature T and the control target value T0 of the temperature difference control unit can be set to 2K, 1.5K, 1K, etc.

[0018] Further, when the actual temperature T of the liquid nitrogen at the outlet of the high-temperature superconducting cable is greater than the set upper limit value T H Manual control should be carried out. For example, if the temperature continues to rise by 2°C, the power transmission line of the high-temperature superconducting cable should be cut off to prevent quench.

[0019] The beneficial effects of the present invention are as follows:

[0020] The present invention adopts a mixed adjustment method mainly based on the cable energization current value and supplemented by the liquid nitrogen temperature value at the cable outlet, which increases the timeliness of the temperature adjustment of the cooling system, reduces the fluctuation of the cooling system temperature with the change of the energization current, shortens the temperature adjustment time, and increases the stability of the system.

[0021] The present invention performs hierarchical adjustment according to the unit refrigeration power consumption of the adjustment equipment, achieving temperature control while minimizing the system energy consumption as much as possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 is a schematic diagram of the cooling system and monitoring system of the high-temperature superconducting cable of the present invention;

[0024] Figure 2 is a schematic diagram of the temperature control method of the cooling system of the high-temperature superconducting cable of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0026] This embodiment takes the cooling system of a three-phase AC high-temperature superconducting cable as an example. For example Figure 1As shown in the figure. The cooling system consists of a liquid storage tank 1, a liquid nitrogen pump box 2, a liquid nitrogen pump 3, a cryogenic system, a high-temperature superconducting cable 10, a buffer tank 11, and a transformer 12; the cryogenic system consists of a refrigerator refrigeration system 4, a decompression evaporation refrigeration system 6, a first bypass valve 8, and a second bypass valve 9. The liquid nitrogen pump 3 is placed in the liquid nitrogen pump box 2. The refrigerator refrigeration system 4 includes a refrigerator 5, and the decompression evaporation refrigeration system 6 includes a vacuum machine 7. The measuring points of the monitoring system are composed of cable outlet temperature measuring points 13, 14, 15, a flowmeter 16, and three-phase current measuring points 17. The circulating liquid nitrogen flows into the buffer tank 11 from the B-phase and C-phase cables of the high-temperature superconducting cable 10 respectively, and then flows out from the A-phase cable. The outflowing liquid nitrogen flows into the liquid nitrogen pump box 2, is pressurized by the liquid nitrogen pump 3, enters the refrigerator refrigeration system 4 or the decompression evaporation refrigeration system 6 for heat exchange and cooling. After the liquid nitrogen is supercooled, it flows into the high-temperature superconducting cable through the cable liquid inlet pipe to cool the superconducting cable, and finally flows back to the liquid nitrogen pump box to start a new round of circulation.

[0027] The temperature control method of the high-temperature superconducting cable cooling system adopted in this embodiment first obtains the required refrigeration capacity through the magnitude of the cable current, then adjusts the refrigerator 5, the liquid nitrogen pump 3, and the vacuum machine 7 in stages according to the high and low energy consumption of the refrigeration equipment, and finally uses the liquid nitrogen temperature at the cable outlet temperature measuring point 13 as an auxiliary adjustment. The present invention can respond in a timely manner to the change of the system heat load caused by the change of the transmission current of the high-temperature superconducting cable, can reduce the large fluctuation of the temperature of the circulating liquid nitrogen, increase the stability of the cooling system, and the control method is as Figure 2 shown.

[0028] The circulating liquid nitrogen temperature of the cooling system adopts an adjustment method mainly based on the cable energization current value and supplemented by the liquid nitrogen temperature value at the cable outlet. This adjustment method is completed by the current temperature control unit, the temperature difference control unit, the cooling capacity adjustment unit, and the command output module.

[0029] The current temperature control unit 21 described above includes a first setting module 24, and the refrigeration capacity Q0 required to maintain the circulating liquid nitrogen temperature when not energized is input through the first setting module 24. The current temperature control unit 21 receives the real-time current data from the monitoring system, and uses the relationship between the increased refrigeration capacity and the change of the cable energization current to convert the real-time current data into the increased refrigeration capacity ΔQ required by the high-temperature superconducting cable cooling system under this current, and outputs it to the cooling capacity adjustment unit 23.

[0030] The temperature difference control unit 22 described above includes a second setting module 25, a first judgment module 28, and a deviation setting module 29. The control target value T0 and the upper limit value T of the liquid nitrogen temperature at the outlet of the high-temperature superconducting cable are input through the second setting module 25 h; Receive the real-time temperature T signal of the liquid nitrogen at the cable outlet from the monitoring system. When the deviation between the real-time temperature T signal and the control target value T0 is greater than 2K, output an alarm signal to the alarm module 40, manually input the deviation instruction S% according to the temperature difference (T - T0) and output it to the cooling capacity adjustment unit for auxiliary adjustment; when the real-time temperature T is greater than the control temperature upper limit value T h , output an alarm signal to the alarm module 40, and at the same time send the signal to the instruction output module 31; if the temperature continues to rise by 2°C, the power transmission line of the high-temperature superconducting cable should be cut off to prevent quench.

[0031] The described cooling capacity adjustment unit: Receive the comprehensive input quantity ΔQ(1 + S%) from the current temperature control unit and the temperature difference control unit, and convert this comprehensive input quantity ΔQ(1 + S%) into the refrigeration machine power ΔP, liquid nitrogen pump flow rate ΔL, and vacuum pump output ΔW that should be increased, and then output them to the instruction output module.

[0032] The described cooling capacity adjustment unit includes a third setting module 26, a calculation module 27, and a second judgment module 30; input the rated power P of the refrigeration machine through the third setting module 26 e , the rated flow rate L of the liquid nitrogen pump e , the rated output W of the vacuum pump e , and the refrigeration machine power P0, liquid nitrogen pump flow rate L0, and vacuum pump output W0 when maintaining the circulating liquid nitrogen temperature when the high-temperature superconducting cable is not powered on; calculate the remaining cooling capacity adjustment margins Q1, Q2, and Q3 of the refrigeration machine, liquid nitrogen pump, and vacuum pump through the calculation module 27; the described second judgment module 30 receives the comprehensive input quantity ΔQ(1 + S%) from the current temperature control unit and the temperature difference control unit and the output parameters Q1, Q2, Q3 of the calculation module, and enters hierarchical adjustment.

[0033] The hierarchical adjustment method adopted by the described cooling capacity adjustment unit: Taking the refrigeration machine, liquid nitrogen pump, and vacuum pump as the priority adjustment order, when ΔQ(1 + S%) ≤ Q1, adjust the refrigeration machine power; when Q1 < ΔQ(1 + S%) ≤ Q1 + Q2, adjust the refrigeration machine power to the rated value and then adjust the liquid nitrogen pump flow rate; when Q1 + Q2 < ΔQ(1 + S%) ≤ Q1 + Q2 + Q3, adjust the refrigeration machine power and the liquid nitrogen pump flow rate to the rated value, and then adjust the vacuum pump output for vacuum evaporation refrigeration; when ΔQ > Q1 + Q2 + Q3, adjust the refrigeration machine power, liquid nitrogen pump flow rate, and vacuum pump output to the rated value, and output an alarm signal to the alarm module 40.

[0034] The command output module 31 receives signals from the cooling capacity adjustment unit 23 and the temperature difference control unit 22. When only the signal from the cooling capacity adjustment unit 23 is received, the adjustment rate v0 is set and the command is sent to the refrigerator 5, the liquid nitrogen pump 3 and the vacuum machine 7, and the refrigerator power is gradually adjusted to P0+ΔP, the liquid nitrogen pump flow is adjusted to L0+ΔL, and the vacuum machine output is W0+ΔW; when the signal from the temperature difference control unit 22 is received, the signal from the cooling capacity adjustment unit 23 is bypassed, and the manual control interface 32 is directly popped up to manually control the refrigerator power, liquid nitrogen pump flow, vacuum machine output and the disconnection of the high-temperature superconducting circuit, and send the command to the device end 33 (refrigerator, liquid nitrogen pump and vacuum machine).

[0035] The hierarchical adjustment method selects the priority according to the energy consumption of the refrigerator and liquid nitrogen pump; the vacuum machine adjusts the pressure and temperature in the subcooler by adjusting the suction volume, but the amount of liquid nitrogen consumed is large, and liquid nitrogen needs to be replenished in a linked manner, so the adjustment priority is set to the lowest.

[0036] The relationship between the increase in cooling capacity and the change in cable current is generally proportional. During the debugging or testing phase of the high-temperature superconducting cable cooling system, the relationship between the increase in cooling capacity ΔQ and the change in cable current is obtained and expressed by a fitting formula or curve.

[0037] The temperature difference control unit can set the deviation judgment value between the real-time temperature T and the control target value T0 to 2K, 1.5K, 1K, etc. according to the control accuracy requirements.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A temperature control method for a high-temperature superconducting cable cooling system, characterized in that: The circulating liquid nitrogen temperature of the cooling system is regulated mainly by the cable current value and supplemented by the liquid nitrogen temperature value at the cable outlet. This regulation method is completed by the current temperature control unit, temperature difference control unit, cooling capacity adjustment unit and instruction output module. The current temperature control unit: inputs the cooling capacity Q0 required to maintain the temperature of the circulating liquid nitrogen when no power is supplied, receives real-time current data from the monitoring system, converts the real-time current data into the increased cooling capacity ΔQ required by the high-temperature superconducting cable cooling system under the current, and outputs the increased cooling capacity ΔQ to the cooling capacity adjustment unit; The temperature difference control unit is input with the control target value T0 and upper limit value T of the liquid nitrogen temperature at the outlet of the high-temperature superconducting cable. h Receive the real-time temperature T signal of liquid nitrogen at the cable outlet from the monitoring system. When the deviation between the real-time temperature T signal and the control target value T0 is greater than 2K, an alarm signal is output. The deviation instruction S% is manually input according to the temperature difference (T-T0) and output to the cooling capacity adjustment unit for auxiliary adjustment. When the real-time temperature T is greater than the control temperature upper limit T h When an alarm occurs, the alarm signal is output and sent directly to the command output module; The cooling capacity adjustment unit: input the rated power of the refrigerator P e , Liquid nitrogen pump rated flow L e , Vacuum machine rated output W e and the refrigerator power P0, liquid nitrogen pump flow L0, and vacuum machine output W0 when the circulating liquid nitrogen temperature is maintained when the high-temperature superconducting cable is not powered; receiving the comprehensive input ΔQ (1+S%) from the current temperature control unit and the temperature difference control unit, and converting this comprehensive input ΔQ (1+S%) into the refrigerator power ΔP, liquid nitrogen pump flow ΔL, and vacuum machine output ΔW that should be increased, and then outputting them to the command output module; The command output module receives signals from the cooling capacity adjustment unit and the temperature difference control unit. When only the signal from the cooling capacity adjustment unit is received, the adjustment rate v0 is set and the command is sent to the refrigerator, liquid nitrogen pump and vacuum machine, and the refrigerator power is gradually adjusted to P0+ΔP, the liquid nitrogen pump flow is adjusted to L0+ΔL, and the vacuum machine output is W0+ΔW; when the signal from the temperature difference control unit is received, the signal from the cooling capacity adjustment unit is bypassed, and a manual control interface is directly popped up to manually control the refrigerator power, liquid nitrogen pump flow, vacuum machine output and disconnection of the high-temperature superconducting circuit, and the command is sent to the refrigerator, liquid nitrogen pump and vacuum machine; The cooling capacity adjustment unit includes a third setting module, a calculation module and a second judgment module; the rated power P of the refrigerator is input through the third setting module. e , Liquid nitrogen pump rated flow L e , Vacuum machine rated output W e and the refrigerator power P0, liquid nitrogen pump flow L0, and vacuum machine output W0 when the circulating liquid nitrogen temperature is maintained when the high-temperature superconducting cable is not powered; the residual cooling capacity adjustment margins Q1, Q2, and Q3 of the refrigerator, liquid nitrogen pump, and vacuum machine are calculated by the calculation module; the judgment module receives the comprehensive input ΔQ (1+S%) from the current temperature control unit and the temperature difference control unit and the output parameters Q1, Q2, and Q3 of the calculation module, and enters a hierarchical adjustment; the hierarchical adjustment is as follows: the priority is selected according to the energy consumption of the refrigerator and the liquid nitrogen pump; the vacuum machine adjusts the pressure and temperature in the subcooler by adjusting the suction volume, and liquid nitrogen needs to be replenished in a linked manner, and the adjustment priority is set to the lowest; The cooling capacity adjustment margin Q1 of the refrigerator is determined by (P e -P0) × COP, where COP is the energy efficiency ratio of the refrigerant; the liquid nitrogen pump cooling capacity adjustment margin Q2 is calculated by (L e -L0)×ΔT×C P Calculated, where ΔT is the temperature difference between the liquid nitrogen inlet and outlet of the cable, C P is the average specific heat of cooling liquid nitrogen; the remaining adjustment margin of vacuum machine cooling capacity Q3 is determined by G LN2 ×r n2 ×ρ is calculated, where ρ is the density of cooling liquid nitrogen, G LN2 is the amount of liquid nitrogen consumed, r n2 is the latent heat of vaporization of liquid nitrogen, G LN2 and r n2 It is related to the vacuum machine's pumping speed, and the corresponding relationship is obtained during system commissioning.

2. The temperature control method of a high-temperature superconducting cable cooling system according to claim 1, characterized in that: The cooling capacity adjustment unit adopts a graded adjustment method: when ΔQ (1 + S%) ≤ Q1, the refrigerator power is adjusted; when Q1 < ΔQ (1 + S%) ≤ Q1 + Q2, the refrigerator power is adjusted to the rated value and then the liquid nitrogen pump flow is adjusted; when Q1 + Q2 < ΔQ (1 + S%) ≤ Q1 + Q2 + Q3, the refrigerator power and the nitrogen pump flow are adjusted to the rated value and then the vacuum machine output is adjusted to perform decompression evaporation refrigeration; when ΔQ > Q1 + Q2 + Q3, the refrigerator power, the liquid nitrogen pump flow and the vacuum machine output are adjusted to the rated value and then an alarm signal is output.

3. The temperature control method of a high-temperature superconducting cable cooling system according to claim 1, characterized in that: The cooling capacity regulation method is determined by the high-temperature superconducting cable cooling system: the cooling capacity of the closed cooling system cooled by the refrigerator is regulated by the refrigerator and the liquid nitrogen pump; the cooling capacity of the open cooling system cooled by reduced pressure is regulated by the vacuum machine and the liquid nitrogen pump; the cooling capacity of the mixed cooling system is regulated by the refrigerator, the liquid nitrogen pump and the vacuum machine.

4. The temperature control method of a high-temperature superconducting cable cooling system according to claim 1, characterized in that: The current temperature control unit converts real-time current data into the increased cooling capacity ΔQ required by the high-temperature superconducting cable cooling system under the current by utilizing the changing relationship between the increased cooling capacity and the current flowing through the cable.

5. The temperature control method of a high-temperature superconducting cable cooling system according to claim 4, characterized in that: During the debugging or testing phase of the high-temperature superconducting cable cooling system, the relationship between the increased cooling capacity ΔQ and the cable current is obtained and expressed using a fitting formula or curve.

6. The temperature control method of a high-temperature superconducting cable cooling system according to claim 1, characterized in that: The temperature difference control unit sets the deviation judgment value between the real-time temperature T and the control target value T0 to 2K, 1.5K and 1K according to the control accuracy requirement.

7. The temperature control method of a high-temperature superconducting cable cooling system according to claim 1, characterized in that: When the actual temperature T of the liquid nitrogen at the outlet of the high-temperature superconducting cable is greater than the set upper limit value T H , it should be manually controlled. If the temperature continues to rise by 2°C, the high-temperature superconducting cable transmission line should be cut off to prevent quenching.

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