JP7617885B2 - Refrigeration machine, control device, control method, and program - Google Patents

Description

This disclosure relates to a refrigerator, a control device, a control method, and a program.

Patent Document 1 discloses a method of changing the nozzle flow area by mechanically operating nozzle vanes at the inlet of the impeller of the expansion turbine with an external actuator. Patent Document 2 discloses a method of changing the operating temperature of the expansion turbine by opening and closing a bypass valve. Patent Document 3 discloses a refrigerator used to cool superconducting power equipment.

Japanese Patent Application Publication No. 6-137101 JP 2018-066511 A JP 2022-109068 A

Generally, the refrigeration capacity of a refrigerator is adjusted by changing the compressor speed or the pressure within the system. The expansion turbine is always operated at the rated speed. However, the expansion turbine is designed so that the adiabatic efficiency is maximized at the flow rate and pressure at the rated operating point, and the adiabatic efficiency decreases under flow rate and pressure conditions that deviate from the design point. The adiabatic efficiency affects the amount of refrigeration generated by the expansion turbine. Therefore, if the adiabatic efficiency deteriorates, the refrigeration capacity decreases and the COP also decreases, causing the efficiency of the entire refrigerator to deteriorate. "COP" is an abbreviation for coefficient of performance.

When the compressor speed changes due to fluctuations in heat load, it is possible to operate the chiller efficiently without reducing the adiabatic efficiency of the expansion turbine by changing the volumetric flow rate of the expansion turbine.

As a method for changing the volumetric flow rate of the expansion turbine, it is possible to change the flow passage area of the nozzle, as disclosed in Patent Document 1. However, with this method, the internal structure becomes complex due to the inclusion of components with moving parts, which may lead to an increased risk of failure and maintenance frequency. For this reason, it is not suitable for cooling superconducting power equipment used as part of infrastructure functions, for example.

As a method for changing the volumetric flow rate of the expansion turbine, it is possible to change the operating temperature of the expansion turbine, as disclosed in Patent Document 2. However, this method requires multiple low-temperature automatic valves to switch the flow paths, which may lead to a risk of failure and increased costs. Therefore, a simpler configuration is desired.

The purpose of this disclosure is to make it easier to avoid a decrease in the adiabatic efficiency of the expansion turbine with a simple equipment configuration.

Some aspects of this disclosure are described below.

[1]
A turbo compressor that compresses a refrigerant;
an expansion turbine for expanding the refrigerant;
a first refrigerant line connecting an outlet of the compressor and an inlet of the expansion turbine;
a second refrigerant line connecting an outlet of the expansion turbine and an inlet of the compressor;
a main heat exchanger that exchanges heat of the refrigerant between the first refrigerant line and the second refrigerant line;
a secondary heat exchanger that performs heat exchange between the refrigerant and an external fluid, the secondary heat exchanger being located downstream of the main heat exchanger in the first refrigerant line or upstream of the main heat exchanger in the second refrigerant line;
A group of sensors attached to at least the first refrigerant line and the second refrigerant line;
a control device that adjusts a rotation speed of the compressor in accordance with a target capacity for cooling the fluid, and adjusts a rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and sensor values obtained from the group of sensors.

[2]
The control device acquires at least measured values of pressure and temperature at the inlet of the expansion turbine and measured values of pressure and temperature at the outlet of the expansion turbine as the sensor values, and adjusts the rotation speed of the expansion turbine by calculating a set value of the rotation speed of the expansion turbine with reference to the acquired measured values and characteristic data that defines a volumetric flow rate when the pressure and temperature of the refrigerant are at a reference pressure and a reference temperature, respectively, for each combination of the rotation speed of the compressor and a pressure ratio at the inlet and outlet of the compressor.

[3]
The refrigeration machine according to [2], wherein the control device calculates a volumetric flow rate Q at the outlet of the expansion turbine by referring to the characteristic data and measured values of the pressure and temperature at the outlet of the expansion turbine, calculates a theoretical adiabatic head H of the expansion turbine by referring to the measured values of the pressure and temperature at the inlet of the expansion turbine and a measured value of the pressure or temperature at the outlet of the expansion turbine, and calculates r at which a specific speed N expressed by an equation N = (2πr√Q)/( ^H0.75 ) falls within a reference range as a setting value for a rotation speed of the expansion turbine.

[4]
The control device further acquires a measured pressure value at the inlet of the compressor and a measured pressure value at the outlet of the compressor as the sensor values, and calculates a volumetric flow rate Q at the outlet of the expansion turbine in accordance with an equation Q = (Q1P1T2)/(T1P2), where _Q1 is a volumetric flow rate defined in the characteristic data corresponding to a combination of a ratio of the measured pressure value at the inlet of the compressor to the measured pressure value at the outlet of the _compressor and a rotation speed of the compressor _{, P1} is the _{reference pressure , T1} is the reference temperature, and P2 and _T2 are the measured pressure and temperature values at _the outlet of the expansion turbine, respectively.

[5]
The refrigeration machine according to [3] or [4], wherein the control device estimates enthalpy h _{in_r} and entropy at the inlet of the expansion turbine from measured values of pressure and temperature at the inlet of the expansion turbine, calculates theoretical enthalpy h _{out_i} at the outlet of the expansion turbine from the estimated entropy and the measured value of pressure or temperature at the _outlet of the expansion turbine, and calculates a theoretical adiabatic head H of the expansion turbine in accordance with an equation H = h _{in_r} - h out_i.

[6]
The refrigerator according to any one of [3] to [5], wherein the reference range is 0.6 or more and 0.7 or less.

[7]
The refrigeration machine according to any one of [2] to [6], wherein the control device calculates a set value of a rotation speed of the expansion turbine when the control device detects a fluctuation in a rotation speed of the compressor or when a certain time has elapsed since the fluctuation in the rotation speed of the compressor.

[8]
A control device for controlling a refrigerant cycle including a turbo compressor that compresses a refrigerant, an expansion turbine that expands the refrigerant, a first refrigerant line that connects an outlet of the compressor and an inlet of the expansion turbine, a second refrigerant line that connects an outlet of the expansion turbine and an inlet of the compressor, a main heat exchanger that performs heat exchange of the refrigerant between the first refrigerant line and the second refrigerant line, and a secondary heat exchanger that performs heat exchange between the refrigerant and an external fluid downstream of the main heat exchanger of the first refrigerant line or upstream of the main heat exchanger of the second refrigerant line,
A communication unit that communicates with at least a group of sensors attached to the first refrigerant line and the second refrigerant line;
a control unit that adjusts the rotation speed of the compressor in accordance with a target capacity for cooling the fluid, and adjusts the rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and sensor values obtained from the group of sensors via the communication unit.

[9]
A control method for controlling a refrigerant cycle including a turbo compressor that compresses a refrigerant, an expansion turbine that expands the refrigerant, a first refrigerant line that connects an outlet of the compressor and an inlet of the expansion turbine, a second refrigerant line that connects an outlet of the expansion turbine and an inlet of the compressor, a main heat exchanger that performs heat exchange of the refrigerant between the first refrigerant line and the second refrigerant line, and a secondary heat exchanger that is located downstream of the main heat exchanger of the first refrigerant line or upstream of the main heat exchanger of the second refrigerant line and performs heat exchange between the refrigerant and an external fluid,
Adjusting the rotation speed of the compressor according to a target capacity for cooling the fluid;
acquiring sensor values from a group of sensors attached to at least the first refrigerant line and the second refrigerant line;
A control method for adjusting the rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and the sensor values obtained from the group of sensors.

[10]
A program for controlling a refrigerant cycle including a turbo compressor that compresses a refrigerant, an expansion turbine that expands the refrigerant, a first refrigerant line that connects an outlet of the compressor and an inlet of the expansion turbine, a second refrigerant line that connects an outlet of the expansion turbine and an inlet of the compressor, a main heat exchanger that performs heat exchange of the refrigerant between the first refrigerant line and the second refrigerant line, and a secondary heat exchanger that performs heat exchange between the refrigerant and an external fluid downstream of the main heat exchanger of the first refrigerant line or upstream of the main heat exchanger of the second refrigerant line,
a computer that communicates with a group of sensors attached to at least the first refrigerant line and the second refrigerant line;
A program that executes a process of adjusting the rotation speed of the compressor in accordance with a target capacity for cooling the fluid, and a process of adjusting the rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and sensor values obtained from the group of sensors.

According to the present disclosure, it becomes easier to avoid a decrease in the adiabatic efficiency of the expansion turbine with a simple equipment configuration.

FIG. 1 is a diagram illustrating a configuration of a refrigerator according to an embodiment of the present disclosure. 4 is a graph showing an example of characteristic data related to a compressor according to an embodiment of the present disclosure. FIG. 2 is a block diagram showing a configuration of a control device according to an embodiment of the present disclosure. 5 is a flowchart illustrating an operation of a control device according to an embodiment of the present disclosure. FIG. 13 is a diagram illustrating a configuration of a refrigerator according to a modified example of the embodiment of the present disclosure.

Embodiments of the present disclosure are described below with reference to the figures.

In each figure, the same or corresponding parts are given the same reference numerals. In the description of this embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

The configuration of the refrigerator 10 according to this embodiment will be described with reference to FIG.

The refrigerator 10 includes a first refrigerant line 11 and a second refrigerant line 12, as well as a turbo compressor 20, an expansion turbine 30, a main heat exchanger 40, a secondary heat exchanger 50, a sensor group 60, a control device 70, and an adjustment mechanism 80.

The first refrigerant line 11 and the second refrigerant line 12 circulate the refrigerant 13. The first refrigerant line 11 connects the outlet 22 of the compressor 20 and the inlet 31 of the expansion turbine 30. The second refrigerant line 12 connects the outlet 32 of the expansion turbine 30 and the inlet 21 of the compressor 20. The compressor 20 compresses the refrigerant 13. The expansion turbine 30 expands the refrigerant 13 to generate cold. The main heat exchanger 40 recovers cold by exchanging heat of the refrigerant 13 between the first refrigerant line 11 and the second refrigerant line 12. The auxiliary heat exchanger 50 exchanges heat between the refrigerant 13 upstream of the main heat exchanger 40 of the second refrigerant line 12 and an external fluid 14. In this embodiment, the fluid 14 circulates in the fluid line 15.

The sensor group 60 is attached to at least the first refrigerant line 11 and the second refrigerant line 12. In this embodiment, the sensor group 60 includes a first pressure gauge 61, a second pressure gauge 62, a third pressure gauge 63, a fourth pressure gauge 64, a first thermometer 65, a second thermometer 66, and a third thermometer 67.

The second pressure gauge 62, the third pressure gauge 63, and the first thermometer 65 are attached to the first refrigerant line 11. Specifically, the second pressure gauge 62 is provided between the outlet 22 of the compressor 20 and the main heat exchanger 40, and measures the pressure at the outlet 22 of the compressor 20. The third pressure gauge 63 is provided between the main heat exchanger 40 and the inlet 31 of the expansion turbine 30, and measures the pressure at the inlet 31 of the expansion turbine 30. The first thermometer 65 is also provided between the main heat exchanger 40 and the inlet 31 of the expansion turbine 30, and measures the temperature at the inlet 31 of the expansion turbine 30.

The first pressure gauge 61, the fourth pressure gauge 64, and the second thermometer 66 are attached to the second refrigerant line 12. Specifically, the first pressure gauge 61 is provided between the main heat exchanger 40 and the inlet 21 of the compressor 20, and measures the pressure at the inlet 21 of the compressor 20. The fourth pressure gauge 64 is provided between the outlet 32 of the expansion turbine 30 and the auxiliary heat exchanger 50, and measures the pressure at the outlet 32 of the expansion turbine 30. The second thermometer 66 is also provided between the outlet 32 of the expansion turbine 30 and the auxiliary heat exchanger 50, and measures the temperature at the outlet 32 of the expansion turbine 30.

The third thermometer 67 is attached to the fluid line 15. The third thermometer 67 measures the temperature of the fluid 14 downstream of the secondary heat exchanger 50 in the fluid line 15.

The control device 70 controls a refrigerant cycle including the first refrigerant line 11, the second refrigerant line 12, the compressor 20, the expansion turbine 30, the main heat exchanger 40, and the auxiliary heat exchanger 50. Specifically, the control device 70 adjusts the rotation speed of the compressor 20 according to a target capacity for cooling the fluid 14, and adjusts the rotation speed of the expansion turbine 30 according to the rotation speed of the compressor 20 and the sensor values obtained from the sensor group 60. Thus, according to this embodiment, it is easy to avoid a decrease in the adiabatic efficiency of the expansion turbine 30 with a simple equipment configuration.

The adjustment mechanism 80 includes a first inverter 81 and a second inverter 82. The compressor 20 and the expansion turbine 30 can adjust their operation and rotation speed by commands from the first inverter 81 and the second inverter 82, respectively. In this embodiment, the control device 70 supplies power to the first inverter 81 and performs control input/output. That is, the control device 70 adjusts the rotation speed of the compressor 20 via the first inverter 81. The control device 70 supplies power to the second inverter 82 and performs control input/output via the first inverter 81. That is, the control device 70 adjusts the rotation speed of the expansion turbine 30 via the first inverter 81 and the second inverter 82. The power supply and control input/output to the second inverter 82 may be performed directly from the control device 70 without going through the first inverter 81. Alternatively, the power supply and control input/output to the second inverter 82 may be performed from another independent control device.

The first inverter 81 and the second inverter 82 may be built into the control device 70. That is, the adjustment mechanism 80 may be integrated into the control device 70.

In this embodiment, the refrigerator 10 is used to cool superconducting power equipment such as a power transmission cable, a current limiter, or a transformer. The refrigerator 10 cools the superconducting power equipment by using a cryogenic refrigeration cycle that repeats adiabatic compression, isobaric cooling, adiabatic expansion, and isobaric heating. In cooling the superconducting power equipment, a fluid 14 is circulated through the superconducting power equipment. The fluid 14 is, for example, liquid nitrogen, liquid hydrogen, or liquid helium. The fluid 14 rises in temperature due to heat generation in the superconducting power equipment or heat entering the system, but is cooled to a desired temperature by the refrigerator 10. The refrigerator 10 is suitable for cases where a large capacity of refrigeration capacity is required. For example, neon gas or helium gas is used as the refrigerant 13 of the refrigerator 10.

The refrigeration capacity of the refrigerator 10 is adjusted by changing the rotation speed of the compressor 20. When the rotation speed of the compressor 20 changes, if the rotation speed of the expansion turbine 30 remains constant, the adiabatic efficiency of the expansion turbine 30 decreases. The adiabatic efficiency affects the amount of cold generated by the expansion turbine 30. Therefore, if the adiabatic efficiency deteriorates, the refrigeration capacity decreases and the COP also decreases, resulting in a deterioration in the efficiency of the entire refrigerator 10.

The specific speed N is one of the indexes that indicate the adiabatic efficiency of the expansion turbine 30. The specific speed N is expressed by the following formula 1.
N=(2πr√Q)/(H ^0.75 )...Formula 1
In Equation 1, r is the rotation speed [rps] of the expansion turbine 30, Q is the volumetric flow rate [m ³ /s] at the outlet 32 of the expansion turbine 30, and H is the theoretical adiabatic head [J/kg].

The volumetric flow rate Q at the outlet 32 of the expansion turbine 30 is expressed by the following equation 2 according to the ideal gas state equation.
Q=(Q ₁ P ₁ T ₂ )/(T ₁ P ₂ )=(101.35Q ₁ T ₂ )/(273.15P ₂ )...Formula 2
In formula 2, _Q1 is the volume flow rate in the standard state [ ^m3 /s (normal)], _P1 is the pressure in the standard state [kPa], _T1 is the temperature in the standard state [K], _P2 is the pressure at the outlet 32 of the expansion turbine 30 [kPa], and _T2 is the temperature at the outlet 32 of the expansion turbine 30 [K]. The standard state refers to a state of 101.35 kPa and 273.15 K. The volume flow rate _Q1 in the standard state can be obtained in advance as characteristic data as shown in Fig. 2 from the relationship between the rotation speed and pressure ratio of the turbo compressor 20. Here, calculation is performed for an ideal gas, but since there is only a few percent error from calculation for an actual gas, there is no practical problem.

The theoretical adiabatic head H is expressed by the following equation 3 using state quantities of the inlet 31 of the expansion turbine 30 and the state quantities of the outlet 32 of the expansion turbine 30.
H=h _{in_r} - h _{out_i} ...Formula 3
In Equation 3, h _{in_r} is the enthalpy [kJ/kg] at the inlet 31 of the expansion turbine 30, and h _{out_i} is the theoretical enthalpy [kJ/kg] at the outlet 32 of the expansion turbine 30. The enthalpy h _{in_r} at the inlet 31 of the expansion turbine 30 is estimated from the pressure and temperature at the inlet 31 of the expansion turbine 30. The theoretical enthalpy h _{out_i} at the outlet 32 of the expansion turbine 30 is estimated from the inlet entropy previously estimated from the pressure and temperature at the inlet 31 of the expansion turbine 30, and the pressure or temperature at the outlet 32 of the expansion turbine 30.

The adiabatic efficiency is highest when the specific speed N is in the range of 0.6 to 0.7. When the adiabatic efficiency is high, the amount of cold generated by the expansion turbine 30 increases, improving the refrigeration capacity and COP.

For example, at the rated operating point, if the rotation speed r of the expansion turbine 30 is 1000 rps, the volumetric flow rate Q at the outlet 32 of the expansion turbine 30 is 0.0197 ^{m 3} /s, and the theoretical adiabatic head H is 15.0 kJ/kg, then from equation 1 the specific speed N is 0.65.

If it is desired to increase the refrigeration capacity from this state, the rotation speed of the compressor 20 is increased. As a result, the theoretical adiabatic head H increases due to an increase in the flow rate and the pressure ratio. If the volumetric flow rate Q at the outlet 32 of the expansion turbine 30 is increased to 0.021 m ³ /s and the theoretical adiabatic head H is increased to 19.0 kJ/kg, the specific speed N becomes 0.56, which is outside the ideal range and reduces the adiabatic efficiency. However, by increasing the rotation speed r of the expansion turbine 30 to 1150 rps, the specific speed N can be improved to 0.65.

Conversely, when it is desired to reduce the refrigeration capacity from the steady state, the rotation speed of the compressor 20 is slowed down. As a result, the theoretical adiabatic head H is reduced due to a decrease in the flow rate and the pressure ratio. If the volumetric flow rate Q at the outlet 32 of the expansion turbine 30 is reduced to 0.018 m ³ /s and the theoretical adiabatic head H is reduced to 12.0 kJ/kg, the specific speed N becomes 0.74, which falls outside the ideal range and reduces the adiabatic efficiency. However, by slowing down the rotation speed r of the expansion turbine 30 to 900 rps, the specific speed N can be improved to 0.66.

As described above, the specific speed N of the expansion turbine 30 changes depending on the operating state of the compressor 20, so if the rotation speed r of the expansion turbine 30 is constant, this leads to a decrease in adiabatic efficiency. In this embodiment, the rotation speed r of the expansion turbine 30 is varied according to the operating state of the compressor 20, so that the specific speed N can be kept within an ideal range.

The internal components of the expansion turbine 30, such as the nozzle and diffuser, are designed to provide a rated flow rate at the design temperature. A characteristic of the expansion turbine 30 is that when the refrigerant temperature is higher than the design temperature, the volumetric flow rate decreases and the specific speed N also decreases.

According to this embodiment, when the rotation speed of the turbo compressor 20 changes due to a change in the thermal load during steady-state operation of the refrigerator 10, the rotation speed r of the expansion turbine 30 is changed, making it possible to operate the refrigerator 10 efficiently without reducing the adiabatic efficiency of the expansion turbine 30. In other words, while adopting a simple equipment configuration that does not include a variable nozzle or a low-temperature automatic valve, it is possible to set the adiabatic efficiency of the expansion turbine 30 to optimal conditions simply by changing the rotation speed r of the expansion turbine 30.

The configuration of the control device 70 according to this embodiment will be described with reference to FIG. 3.

The control device 70 includes a control unit 71, a memory unit 72, and a communication unit 73.

The control unit 71 includes at least one processor, at least one programmable circuit, at least one dedicated circuit, or any combination of these. The processor is a general-purpose processor such as a CPU or GPU, or a dedicated processor specialized for a specific process. "CPU" is an abbreviation for central processing unit. "GPU" is an abbreviation for graphics processing unit. The programmable circuit is, for example, an FPGA. "FPGA" is an abbreviation for field-programmable gate array. The dedicated circuit is, for example, an ASIC. "ASIC" is an abbreviation for application specific integrated circuit. The control unit 71 executes processes related to the operation of the control unit 70 while controlling each part of the control unit 70.

The memory unit 72 includes at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or any combination thereof. The semiconductor memory is, for example, a RAM, a ROM, or a flash memory. "RAM" is an abbreviation for random access memory. "ROM" is an abbreviation for read only memory. The RAM is, for example, an SRAM or a DRAM. "SRAM" is an abbreviation for static random access memory. "DRAM" is an abbreviation for dynamic random access memory. The ROM is, for example, an EEPROM. "EEPROM" is an abbreviation for electrically erasable programmable read only memory. The flash memory is, for example, an SSD. "SSD" is an abbreviation for solid-state drive. The magnetic memory is, for example, an HDD. "HDD" is an abbreviation for hard disk drive. The memory unit 72 functions, for example, as a main memory device, an auxiliary memory device, or a cache memory. The memory unit 72 stores data used in the operation of the control device 70 and data obtained by the operation of the control device 70.

The communication unit 73 includes at least one communication interface. The communication interface is, for example, an interface corresponding to a wired LAN communication standard such as Ethernet (registered trademark), a wireless LAN communication standard such as IEEE 802.11, an interface corresponding to a mobile communication standard such as LTE, 4G standard, or 5G standard, or an interface corresponding to short-range wireless communication such as Bluetooth (registered trademark). "LAN" is an abbreviation for local area network. "IEEE" is an abbreviation for Institute of Electrical and Electronics Engineers. "LTE" is an abbreviation for Long Term Evolution. "4G" is an abbreviation for 4th generation. "5G" is an abbreviation for 5th generation. The communication unit 73 communicates with the sensor group 60 and the adjustment mechanism 80. The communication unit 73 receives data used in the operation of the control device 70 and transmits data obtained by the operation of the control device 70.

At least some of the functions of the control device 70 are realized by executing a program according to this embodiment in a processor serving as the control unit 71. That is, at least some of the functions of the control device 70 are realized by software. The program causes a computer to execute the operations of the control device 70, thereby causing the computer to function as the control device 70. That is, the computer functions as the control device 70 by executing the operations of the control device 70 in accordance with the program.

The program may be stored in a non-transitory computer-readable medium. Examples of the non-transitory computer-readable medium include flash memory, a magnetic recording device, an optical disk, a magneto-optical recording medium, or a ROM. The program may be distributed, for example, by selling, transferring, or lending portable media such as SD cards, DVDs, or CD-ROMs on which the program is stored. "SD" is an abbreviation for Secure Digital. "DVD" is an abbreviation for digital versatile disc. "CD-ROM" is an abbreviation for compact disc read only memory. The program may be distributed by storing the program in the storage of a server and transferring the program from the server to another computer. The program may be provided as a program product.

For example, a computer temporarily stores a program stored in a portable medium or a program transferred from a server in a main storage device. The computer then reads the program stored in the main storage device with a processor and executes processing according to the read program with the processor. The computer may read the program directly from the portable medium and execute processing according to the program. The computer may execute processing according to the received program each time a program is transferred from the server to the computer. Processing may be executed by a so-called ASP-type service that does not transfer a program from the server to the computer and achieves functions only by issuing execution instructions and obtaining results. "ASP" is an abbreviation for application service provider. Programs include information used for processing by a computer and equivalent to a program. For example, data that is not a direct command to a computer but has properties that define computer processing falls under " equivalent to a program".

Some or all of the functions of the control device 70 may be realized by a programmable circuit or a dedicated circuit as the control unit 71. In other words, some or all of the functions of the control device 70 may be realized by hardware.

The operation of the control device 70 according to this embodiment will be described with reference to FIG. 4. This operation corresponds to the control method according to this embodiment.

The control unit 71 of the control device 70 adjusts the rotation speed of the compressor 20 according to the target capacity for cooling the fluid 14, and adjusts the rotation speed of the expansion turbine 30 according to the rotation speed of the compressor 20 and the sensor value obtained from the sensor group 60 via the communication unit 73.

The procedure for adjusting the rotation speed of the compressor 20 may be the same as that of the conventional method. For example, the control unit 71 of the control device 70 compares the measured temperature value input from the third thermometer 67 via the communication unit 73 with the set temperature value pre-stored in the memory unit 72 or input via the communication unit 73 to determine whether the target for the ability to cool the fluid 14 has been achieved. The control unit 71 increases or decreases the rotation speed of the compressor 20 via the first inverter 81 according to the obtained determination result, that is, so that the difference between the measured temperature value and the set temperature value is eliminated. For example, when the measured temperature value is higher than the set temperature value, the control unit 71 increases the refrigeration capacity by increasing the rotation speed of the compressor 20 via the first inverter 81, since it is necessary to promote cooling.

The following describes the process for adjusting the rotation speed of the expansion turbine 30.

In steps S1 to S5, the control unit 71 of the control device 70 acquires at least the measured values of the pressure and temperature at the inlet 31 of the expansion turbine 30 and the measured values of the pressure and temperature at the outlet 32 of the expansion turbine 30 as sensor values. The control unit 71 adjusts the rotation speed of the expansion turbine 30 by calculating the set value of the rotation speed of the expansion turbine 30 with reference to the acquired measured values and the characteristic data. The characteristic data is data that defines the volumetric flow rate in the standard state for each combination of the rotation speed of the compressor 20 and the pressure ratio of the inlet 21 and the outlet 22 of the compressor 20. The volumetric flow rate in the standard state refers to the volumetric flow rate when the pressure and temperature of the refrigerant 13 are at the reference pressure and the reference temperature, respectively. In general, for turbo compressors, the relationship between the rotation speed, pressure ratio, and volumetric flow rate is specified in an evaluation test or simulation before being installed in a refrigerator, and is recorded as characteristic data. This characteristic data is also necessary to avoid troubles such as surges at start-up. FIG. 2 is a graph that shows the relationship between the volumetric flow rate in the standard state of the compressor 20 and the pressure ratio and the rotation speed. In this embodiment, data defining the relationship represented by this graph is pre-stored as characteristic data in the memory unit 72 of the control device 70.

The processes of steps S1 to S5 are executed when the rotation speed of the compressor 20 fluctuates. That is, when the control unit 71 of the control device 70 detects a fluctuation in the rotation speed of the compressor 20, it calculates the set value of the rotation speed of the expansion turbine 30. Alternatively, the processes of steps S1 to S5 may be executed when a certain time has elapsed since the fluctuation in the rotation speed of the compressor 20. That is, the control unit 71 of the control device 70 may calculate the set value of the rotation speed of the expansion turbine 30 when a certain time has elapsed since the fluctuation in the rotation speed of the compressor 20.

The following describes the details of steps S1 to S5.

In step S1, the control unit 71 of the control device 70 acquires the measured pressure value at the inlet 21 of the compressor 20 and the measured pressure value at the outlet 22 of the compressor 20 as sensor values. The control unit 71 identifies the volumetric flow rate under standard conditions defined in the characteristic data in correspondence with the combination of the ratio of the measured pressure value at the inlet 21 of the compressor 20 to the measured pressure value at the outlet 22 of the compressor 20 and the rotation speed of the compressor 20.

Specifically, the control unit 71 of the control device 70 acquires the measured value of the pressure at the inlet 21 of the compressor 20 from the first pressure gauge 61 via the communication unit 73. The control unit 71 acquires the measured value of the pressure at the outlet 22 of the compressor 20 from the second pressure gauge 62 via the communication unit 73. For the rotation speed of the compressor 20, the control unit 71 acquires the set value calculated when adjusting the rotation speed of the compressor 20. Alternatively, the control unit 71 may acquire the measured value via the communication unit 73 from a sensor additionally provided to measure the rotation speed of the compressor 20. The control unit 71 calculates the ratio of the measured value of the pressure at the inlet 21 of the compressor 20 to the measured value of the pressure at the outlet 22 of the compressor 20 as the pressure ratio of the compressor 20. The control unit 71 refers to the characteristic data previously stored in the memory unit 72 and calculates the volumetric flow rate in the standard state corresponding to the combination of the calculated value of the pressure ratio of the compressor 20 and the set value or measured value of the rotation speed of the compressor 20. That is, the control unit 71 estimates the volumetric flow rate under standard conditions from the relationship between the pressure ratio and rotation speed of the compressor 20.

In step S2, the control unit 71 of the control device 70 acquires, as sensor values, the measured values of the pressure and temperature at the outlet 32 of the expansion turbine 30. The control unit 71 calculates the volumetric flow rate Q at the outlet 32 of the expansion turbine 30 in accordance with the formula Q=( _{Q1P1T2) /} ( _{T1P2 )} , where Q1 is the volumetric flow rate in the standard state identified in step _S1 , _P1 is the reference pressure, _T1 is the reference temperature, and _{P2 and T2} are the measured values of the pressure and temperature at the outlet 32 of the expansion turbine 30, respectively.

Specifically, the control unit 71 of the control device 70 acquires the measured values of the pressure and temperature at the outlet 32 of the expansion turbine 30 from the fourth pressure gauge 64 and the second thermometer 66 via the communication unit 73. The control unit 71 calculates the volumetric flow rate Q at the outlet 32 of the expansion turbine 30 using Equation 2 from the estimated value of the volumetric flow rate under standard conditions obtained in step S1 and the measured values of the pressure and temperature at the outlet 32 of the expansion turbine 30.

In step S3, the control unit 71 of the control device 70 acquires, as sensor values, the measured values of the pressure and temperature at the inlet 31 of the expansion turbine 30. The control unit 71 estimates the enthalpy h _{in_r} and entropy at the inlet 31 of the expansion turbine 30 from the measured values of the pressure and temperature at the inlet 31 of the expansion turbine 30. The control unit 71 calculates the theoretical enthalpy h _{out_i} at the outlet 32 of the expansion turbine 30 from the estimated entropy and the measured values of the pressure or temperature at the outlet 32 of the expansion turbine 30 acquired in step S2. The control unit 71 calculates the theoretical adiabatic head H of the expansion turbine 30 according to the formula H=h _{in_r} -h _{out_i} .

Specifically, the control unit 71 of the control device 70 acquires the measured values of pressure and temperature at the inlet 31 of the expansion turbine 30 from the third pressure gauge 63 and the first thermometer 65 via the communication unit 73. The control unit 71 estimates the inlet enthalpy and inlet entropy from the measured values of pressure and temperature at the inlet 31 of the expansion turbine 30. The control unit 71 estimates the ideal outlet enthalpy from the estimated value of the inlet entropy and the measured value of the pressure or temperature at the outlet 32 of the expansion turbine 30 acquired in step S2. The control unit 71 calculates the theoretical adiabatic head H of the expansion turbine 30 from the estimated value of the ideal outlet enthalpy and the estimated value of the inlet enthalpy using Equation 3. That is, the control unit 71 estimates the theoretical adiabatic head H by calculating the difference between the estimated value of the ideal outlet enthalpy and the estimated value of the inlet enthalpy.

In step S4, the control unit 71 of the control device 70 calculates, as a set value of the rotation speed of the expansion turbine 30, r at which the specific speed N expressed by the formula N=(2πr√Q)/(H 0.75 ) falls within a reference range, from the volumetric flow rate Q of the outlet 32 of the expansion turbine 30 calculated in steps S1 and S2 with reference to the measured values of the pressure and temperature of the outlet 32 of the expansion turbine 30 and the characteristic data, and the theoretical adiabatic head H of the expansion turbine 30 calculated in step S3 with reference to the measured values of ^the pressure and temperature of the inlet 31 of the expansion turbine 30 and the measured value of the pressure or temperature of the outlet 32 of the expansion turbine 30. That is, the control unit 71 calculates, by back-calculation using formula 1, the optimal rotation speed of the expansion turbine 30 from the calculated value of the volumetric flow rate Q of the outlet 32 of the expansion turbine 30 obtained in step S2, the calculated value of the theoretical adiabatic head H of the expansion turbine 30 obtained in step S3, and the reference range of the specific speed N. In this embodiment, the reference range is set in advance to 0.6 to 0.7, but may be changed as appropriate. The reference range may be set as a single reference value.

In step S5, the control unit 71 of the control device 70 adjusts the rotation speed of the expansion turbine 30 via the first inverter 81 and the second inverter 82 by outputting the set value of the rotation speed of the expansion turbine 30 calculated in step S4 to the first inverter 81 via the communication unit 73. Alternatively, the control unit 71 may adjust the rotation speed of the expansion turbine 30 via the second inverter 82 by directly outputting the set value of the rotation speed of the expansion turbine 30 calculated in step S4 to the second inverter 82 via the communication unit 73.

In this embodiment, the control device 70 executes the processes from step S1 to step S4 to calculate the ideal rotation speed of the expansion turbine 30 for the reference specific speed in a certain operating state. For example, if the reference value of the specific speed N is 0.65, the control device 70 can calculate the rotation speed at which the specific speed N becomes 0.65 by back-calculating using Equation 1. In step S5, the control device 70 outputs a rotation speed command to the second inverter 82, thereby automatically adjusting the rotation speed of the expansion turbine 30 to a rotation speed at which high efficiency can be obtained in accordance with the operating state of the compressor 20.

The configuration of a refrigerator 10a according to a modified example of this embodiment will be described with reference to FIG. 5.

The configuration of the refrigerator 10a is similar to that of the refrigerator 10 shown in FIG. 1, except that the expansion turbine 30 is disposed between the outlet of the auxiliary heat exchanger 50 and the inlet of the main heat exchanger 40. In this modification, the auxiliary heat exchanger 50 exchanges heat between the refrigerant 13 downstream of the main heat exchanger 40 in the first refrigerant line 11 and the external fluid 14.

In the refrigerator 10 shown in FIG. 1, a third pressure gauge 63 and a first thermometer 65 are provided between the main heat exchanger 40 and the expansion turbine 30, whereas in the refrigerator 10a shown in FIG. 5, a third pressure gauge 63 and a first thermometer 65 are provided between the auxiliary heat exchanger 50 and the expansion turbine 30. In the refrigerator 10 shown in FIG. 1, a fourth pressure gauge 64 and a second thermometer 66 are provided between the expansion turbine 30 and the auxiliary heat exchanger 50, whereas in the refrigerator 10a shown in FIG. 5, a fourth pressure gauge 64 and a second thermometer 66 are provided between the expansion turbine 30 and the main heat exchanger 40.

The functions and operations of the turbo compressor 20, expansion turbine 30, main heat exchanger 40, secondary heat exchanger 50, sensor group 60, control device 70, and adjustment mechanism 80 are the same as those of the refrigerator 10 shown in FIG. 1, so a description thereof will be omitted.

The present disclosure is not limited to the above-described embodiments. For example, multiple blocks shown in the block diagram may be integrated, or one block may be divided. Instead of executing multiple steps shown in the flowchart in chronological order as described, each step may be executed in parallel or in a different order depending on the processing capacity of the device executing each step, or as needed. Other modifications are possible without departing from the spirit of the present disclosure.

REFRIGERATION SYSTEM AND METHOD FOR CARRYING OUT THE DISCLOSURE 10, 10a Refrigerating machine 11 First refrigerant line 12 Second refrigerant line 13 Refrigerant 14 Fluid 15 Fluid line 20 Compressor 21 Inlet 22 Outlet 30 Expansion turbine 31 Inlet 32 Outlet 40 Main heat exchanger 50 Auxiliary heat exchanger 60 Sensor 61 First pressure gauge 62 Second pressure gauge 63 Third pressure gauge 64 Fourth pressure gauge 65 First thermometer 66 Second thermometer 67 Third thermometer 70 Control device 71 Control unit 72 Memory unit 73 Communication unit 80 Adjustment mechanism 81 First inverter 82 Second inverter

Claims (10)

A turbo compressor that compresses a refrigerant;
an expansion turbine for expanding the refrigerant;
a first refrigerant line connecting an outlet of the compressor and an inlet of the expansion turbine;
a second refrigerant line connecting an outlet of the expansion turbine and an inlet of the compressor;
a main heat exchanger that exchanges heat of the refrigerant between the first refrigerant line and the second refrigerant line;
a secondary heat exchanger that performs heat exchange between the refrigerant and an external fluid, the secondary heat exchanger being located downstream of the main heat exchanger in the first refrigerant line or upstream of the main heat exchanger in the second refrigerant line;
A group of sensors attached to at least the first refrigerant line and the second refrigerant line;
a control device that adjusts a rotation speed of the compressor in accordance with a target capacity for cooling the fluid, and adjusts a rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and sensor values obtained from the group of sensors. The refrigeration machine according to claim 1, wherein the control device acquires at least the measured values of the pressure and temperature at the inlet of the expansion turbine and the measured values of the pressure and temperature at the outlet of the expansion turbine as the sensor values, and calculates a set value of the rotation speed of the expansion turbine by referring to the acquired measured values and characteristic data that defines the volumetric flow rate when the pressure and temperature of the refrigerant are at a reference pressure and reference temperature, respectively, for each combination of the rotation speed of the compressor and the pressure ratio at the inlet and outlet of the compressor, thereby adjusting the rotation speed of the expansion turbine. 3. The refrigeration machine according to claim 2, wherein the control device calculates a volumetric flow rate Q at the outlet of the expansion turbine by referring to the characteristic data and measured values of the pressure and temperature at the outlet of the expansion turbine, calculates a theoretical adiabatic head H of the expansion turbine by referring to the measured values of the pressure and temperature at the inlet of the expansion turbine and the measured value of the pressure or temperature at the outlet of the expansion turbine, and calculates r at which a specific speed N expressed by an equation N = (2πr√Q)/( ^H0.75 ) falls within a reference range as a setting value for the rotation speed of the expansion turbine. 4. The refrigeration machine according to claim 3, wherein the control device further acquires a measured pressure value at the inlet of the compressor and a measured pressure value at the outlet of the compressor as the sensor values, and calculates a volumetric flow rate Q at the outlet of the expansion turbine in accordance with an equation Q = (Q1P1T2)/( _{T1P2 ),} where _Q1 is a volumetric flow rate defined in the characteristic data corresponding to a combination of a ratio of the measured pressure value at the inlet of the compressor to the measured pressure value at the outlet of the compressor and a rotation speed of the compressor _{, P1} is the reference pressure _{, T1} is the reference temperature _, and _P2 and _T2 are the measured pressure and temperature values at the outlet of the expansion turbine, respectively. The refrigeration machine according to claim 3, wherein the control device estimates enthalpy h _{in_r} and entropy at the inlet of the expansion turbine from measured values of pressure and temperature at the inlet of the expansion turbine, calculates theoretical enthalpy h _{out_i} at the outlet of the expansion turbine from the estimated entropy and the measured value of pressure or temperature at the outlet of the expansion turbine, and calculates theoretical adiabatic head H of the expansion turbine in accordance with an equation H = h _{in_r} - h _{out_i} . The refrigerator according to claim 3, wherein the reference range is 0.6 or more and 0.7 or less. The refrigerator according to any one of claims 2 to 6, wherein the control device detects a change in the rotation speed of the compressor or calculates a set value for the rotation speed of the expansion turbine when a certain time has elapsed since the change in the rotation speed of the compressor. A control device for controlling a refrigerant cycle including a turbo compressor that compresses a refrigerant, an expansion turbine that expands the refrigerant, a first refrigerant line that connects an outlet of the compressor and an inlet of the expansion turbine, a second refrigerant line that connects an outlet of the expansion turbine and an inlet of the compressor, a main heat exchanger that performs heat exchange of the refrigerant between the first refrigerant line and the second refrigerant line, and a secondary heat exchanger that performs heat exchange between the refrigerant and an external fluid downstream of the main heat exchanger of the first refrigerant line or upstream of the main heat exchanger of the second refrigerant line,
A communication unit that communicates with at least a group of sensors attached to the first refrigerant line and the second refrigerant line;
a control unit that adjusts the rotation speed of the compressor in accordance with a target capacity for cooling the fluid, and adjusts the rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and sensor values obtained from the group of sensors via the communication unit. A control method for controlling a refrigerant cycle including a turbo compressor that compresses a refrigerant, an expansion turbine that expands the refrigerant, a first refrigerant line that connects an outlet of the compressor and an inlet of the expansion turbine, a second refrigerant line that connects an outlet of the expansion turbine and an inlet of the compressor, a main heat exchanger that performs heat exchange of the refrigerant between the first refrigerant line and the second refrigerant line, and a secondary heat exchanger that is located downstream of the main heat exchanger of the first refrigerant line or upstream of the main heat exchanger of the second refrigerant line and performs heat exchange between the refrigerant and an external fluid,
Adjusting the rotation speed of the compressor according to a target capacity for cooling the fluid;
acquiring sensor values from a group of sensors attached to at least the first refrigerant line and the second refrigerant line;
A control method for adjusting the rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and the sensor values obtained from the group of sensors. A program for controlling a refrigerant cycle including a turbo compressor that compresses a refrigerant, an expansion turbine that expands the refrigerant, a first refrigerant line that connects an outlet of the compressor and an inlet of the expansion turbine, a second refrigerant line that connects an outlet of the expansion turbine and an inlet of the compressor, a main heat exchanger that performs heat exchange of the refrigerant between the first refrigerant line and the second refrigerant line, and a secondary heat exchanger that performs heat exchange between the refrigerant and an external fluid downstream of the main heat exchanger of the first refrigerant line or upstream of the main heat exchanger of the second refrigerant line,
a computer that communicates with a group of sensors attached to at least the first refrigerant line and the second refrigerant line;
A program that executes a process of adjusting the rotation speed of the compressor in accordance with a target capacity for cooling the fluid, and a process of adjusting the rotation speed of the expansion turbine in accordance with the rotation speed of the compressor and sensor values obtained from the group of sensors.

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