Method and system for controlling liquid injection cooling of a screw compressor motor of a two-stage heat pump system

Abstract

A two-stage heat pump system screw compressor motor liquid injection cooling control method and system, the control method comprises whether the low-pressure stage motor liquid injection valve and the high-pressure stage motor liquid injection valve are opened based on the motor temperature and the motor temperature difference value of the low-pressure stage compressor and the high-pressure stage compressor of the two-stage heat pump system; the difference value of the oil injection temperature and the set oil injection temperature is used to adjust the electric regulating valve connected at the outlet of the oil cooler; after the low-pressure stage motor liquid injection valve and the high-pressure stage motor liquid injection valve are opened, the outlet oil temperature of the oil cooler is increased to maintain the exhaust temperature consistent with that before the low-pressure stage motor liquid injection valve and the high-pressure stage motor liquid injection valve are opened; at the same time, after the low-pressure stage motor liquid injection valve and the high-pressure stage motor liquid injection valve are opened, whether the low-pressure stage motor liquid injection valve and the high-pressure stage motor liquid injection valve are closed based on the motor temperature and the motor temperature difference value. The application can make the heating capacity of the two-stage heat pump system and the motor temperature more stable when the motor is liquid injected.

Description

Technical Field

[0001] This invention belongs to the field of heat pump technology, specifically relating to a method and system for controlling liquid injection cooling of a screw compressor motor in a two-stage heat pump system. Background Technology

[0002] Heat pumps offer significant performance advantages in heating applications. The core component of a heat pump system is the compressor, with semi-hermetic screw compressors commonly used. In a semi-hermetic screw compressor, the motor is housed within the compressor casing, and the motor's heat is dissipated by the refrigerant flowing through it. With technological advancements, industrial demands for condensing temperatures are increasing. Therefore, heat pumps designed for high condensing temperatures require additional motor cooling measures to ensure proper motor operation. Liquid refrigerant injection directly sprays liquid refrigerant onto the motor winding surface to lower the motor temperature. This method typically involves connecting the liquid refrigerant after the condenser to the injection port on the compressor casing via piping. The usual control logic for liquid refrigerant injection is to start injection when the motor temperature reaches the start point and stop when it drops to the stop point. This control can cause significant fluctuations in motor temperature. Furthermore, liquid refrigerant injection can lower the heat pump's heating capacity and the high-pressure stage compressor's exhaust temperature, affecting the stable operation of a two-stage heat pump system. Summary of the Invention

[0003] The purpose of this invention is to address the problems in the prior art by providing a method and system for controlling liquid injection cooling of a screw compressor motor in a two-stage heat pump system. This method and system make the heating capacity and motor temperature of the two-stage heat pump system more stable during liquid injection, thereby comprehensively improving the stability of the two-stage heat pump system.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for controlling liquid injection cooling of a screw compressor motor in a two-stage heat pump system, comprising:

[0006] The decision to open the liquid injection valves of the low-pressure stage compressor and the high-pressure stage compressor is based on a comprehensive assessment of the motor temperatures and temperature difference between the two-stage heat pump system.

[0007] The electric regulating valve connected to the oil cooler outlet is adjusted based on the difference between the injection temperature and the set injection temperature.

[0008] After opening the low-pressure stage motor injection valve and the high-pressure stage motor injection valve, the outlet oil temperature of the oil cooler is increased to maintain the exhaust temperature at the same level as before the opening of the low-pressure stage motor injection valve and the high-pressure stage motor injection valve. At the same time, after opening the low-pressure stage motor injection valve and the high-pressure stage motor injection valve, a comprehensive judgment is made based on the motor temperature and the motor temperature difference to determine whether to close the low-pressure stage motor injection valve and the high-pressure stage motor injection valve.

[0009] As a preferred approach, the motor temperatures of the low-pressure stage compressor and the high-pressure stage compressor are collected, and the motor temperature difference is calculated.

[0010] Determine if the motor injection valve opens under the following conditions; otherwise, continue collecting motor temperature data:

[0011] The temperature difference between the motors of the low-pressure stage compressor and the high-pressure stage compressor is less than the first threshold temperature difference for opening the motor injection valve and greater than the second threshold temperature difference for opening the motor injection valve. At this time, the motor temperature is greater than the first threshold temperature for opening the motor injection valve.

[0012] When the temperature difference between the motors of the low-pressure stage compressor and the high-pressure stage compressor is greater than the first threshold temperature difference for opening the motor injection valve, the motor temperature is greater than the second threshold temperature for opening the motor injection valve.

[0013] As a preferred option, the outlet oil temperature of the oil cooler and the exhaust temperature of the high-pressure stage compressor are collected;

[0014] Collect the opening status of the injection valve of the low-pressure stage motor and the injection valve of the high-pressure stage motor;

[0015] If the low-pressure stage motor injection valve and the high-pressure stage motor injection valve are closed, the electric regulating valve is controlled by PID. The target value of the PID is the oil outlet temperature of the oil cooler, which is the set oil temperature. After resetting the target adjustment value, the oil outlet temperature of the oil cooler and the exhaust temperature of the high-pressure stage compressor are collected.

[0016] If both the low-pressure stage motor injection valve and the high-pressure stage motor injection valve are open, the PID target value of the electric regulating valve is the oil outlet oil temperature of the oil cooler plus the target adjustment value.

[0017] As a preferred option, the outlet oil temperature of the oil cooler and the exhaust temperature of the high-pressure stage compressor are collected;

[0018] Collect the opening status of the injection valve of the low-pressure stage motor and the injection valve of the high-pressure stage motor;

[0019] If the low-pressure stage motor injection valve and the high-pressure stage motor injection valve are open, the electric regulating valve is controlled by PID. The PID target value is the oil cooler outlet oil temperature plus the target adjustment value. The oil cooler outlet oil temperature and the high-pressure stage compressor discharge temperature are collected and delayed for a set time. If the difference between the high-pressure stage compressor discharge temperature and the discharge temperature before the low-pressure stage motor injection valve and the high-pressure stage motor injection valve are opened is less than the set value, the target adjustment value is increased. At the same time, the PID target value of the electric regulating valve is adjusted to the oil cooler outlet oil temperature plus the target adjustment value, and the subsequent operation is repeated.

[0020] As a preferred approach, after opening the liquid injection valves of the low-pressure stage motor and the high-pressure stage motor, the motor temperatures of the low-pressure stage compressor and the high-pressure stage compressor are collected, and the motor temperature difference is calculated.

[0021] Determine if the motor injection valve closes under the following conditions; otherwise, continue collecting motor temperature data:

[0022] The temperature difference between the motors of the low-pressure stage compressor and the high-pressure stage compressor is less than the temperature difference of the motor injection valve closing threshold. At this time, the motor temperature is less than the first threshold temperature for closing the motor injection valve.

[0023] When the temperature difference between the motors of the low-pressure stage compressor and the high-pressure stage compressor is greater than the temperature difference at which the motor injection valve closes, the motor temperature is less than the second threshold temperature at which the motor injection valve closes.

[0024] As a preferred approach, before collecting the motor temperature of the low-pressure stage compressor and the motor temperature of the high-pressure stage compressor, it is first determined whether the system is in a stable operating state. The condition for determining that the system is in a stable operating state is met: the fluctuation value of the suction pressure of the low-pressure stage compressor and the discharge pressure of the high-pressure stage compressor is less than 50 kPa / min.

[0025] As a preferred embodiment, the two-stage heat pump system includes a low-pressure stage compressor and a high-pressure stage compressor. The outlet of the low-pressure stage compressor is connected to the inlet of the high-pressure stage compressor, the outlet of the high-pressure stage compressor is connected to the inlet of an oil-gas separator, the gas outlet of the oil-gas separator is connected to the inlet of a pressure maintaining valve, the outlet of the pressure maintaining valve is connected to the inlet of the condenser, the outlet of the condenser is connected to the main inlet of the intercooler, the main outlet of the intercooler is connected to the inlet of the main expansion valve, the outlet of the main expansion valve is connected to the inlet of the evaporator, and the outlet of the evaporator is connected to the inlet of the low-pressure stage compressor. The main outlet of the intercooler is also connected to the inlets of the low-pressure stage motor injection valve and the high-pressure stage motor injection valve, respectively. The outlet of the low-pressure stage motor injection valve is connected to the motor injection port of the low-pressure stage compressor, and the outlet of the high-pressure stage motor injection valve is connected to the motor injection port of the high-pressure stage compressor. The condenser and evaporator are also connected to the inlet of an ejector, and the outlet of the ejector is connected to the inlet of the low-pressure stage compressor.

[0026] As a preferred embodiment, the outlet of the condenser is also connected to the inlet of the gas supply branch expansion valve, the outlet of the gas supply branch expansion valve is connected to the branch inlet of the intercooler, the branch outlet of the intercooler is connected to the inlet of the check valve, and the outlet of the check valve is connected to the inlet of the high-pressure stage compressor; the oil outlet of the oil-gas separator is connected to the inlet of the oil cooler, and the outlet of the oil cooler is connected to the oil inlet of the high-pressure stage compressor.

[0027] As a preferred embodiment, the outlet of the condenser is also connected to the inlet of the oil cooler, the outlet of the oil cooler is connected to the inlet of the electric regulating valve, and the outlet of the electric regulating valve is connected to the inlet of the evaporator.

[0028] This invention also proposes a liquid-jet cooling control system for a screw compressor motor in a two-stage heat pump system, comprising:

[0029] The motor injection valve opening determination module is used to comprehensively determine whether to open the low-pressure stage motor injection valve and the high-pressure stage motor injection valve based on the motor temperature and motor temperature difference of the low-pressure stage compressor and the high-pressure stage compressor in a two-stage heat pump system.

[0030] The adjustment module is used to adjust the electric regulating valve connected to the oil cooler outlet based on the difference between the injection temperature and the set injection temperature; and, when the low-pressure stage motor injection valve and the high-pressure stage motor injection valve are opened, the exhaust temperature is maintained at the same level as before the low-pressure stage motor injection valve and the high-pressure stage motor injection valve are opened by increasing the oil temperature at the outlet of the oil cooler.

[0031] The motor injection valve closure determination module is used to determine whether to close the low-pressure motor injection valve and the high-pressure motor injection valve based on the motor temperature and the temperature difference after the low-pressure motor injection valve and the high-pressure motor injection valve are opened.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] The system uses a comprehensive assessment of the motor temperatures of the low-pressure and high-pressure compressors in a two-stage heat pump system, along with their temperature differences, to determine whether to open and close the low-pressure and high-pressure stage motor injection valves. This shortens the opening time of the motor injection valves and reduces fluctuations in the two-stage heat pump system. Simultaneously, when the motor injection valves are open, the electric regulating valve is adjusted in conjunction with the system to address the impact of motor injection on the heat pump's heating capacity. By increasing the injection temperature, the exhaust temperature at the compressor outlet is stabilized, thereby stabilizing the heating capacity of the two-stage heat pump system and effectively improving its stability when the motor injection valves are open.

[0034] Furthermore, before collecting the motor temperature of the low-pressure stage compressor and the motor temperature of the high-pressure stage compressor, the present invention first determines whether the system is in a stable operating state, so as to avoid control failure caused by unstable system parameters. Attached Figure Description

[0035] Figure 1 A schematic diagram of the structure of a two-stage heat pump system according to an embodiment of the present invention;

[0036] Figure 2 Flowchart of the liquid injection valve opening control method for the screw compressor motor of the two-stage heat pump system in this embodiment of the invention;

[0037] Figure 3 Flowchart of the control method for the electric regulating valve of the screw compressor in a two-stage heat pump system according to an embodiment of the present invention;

[0038] Figure 4 Flowchart of the cooling control method for closing the liquid injection valve of the screw compressor motor in a two-stage heat pump system in this embodiment of the invention;

[0039] Figure 5 A block diagram of the liquid-injection cooling control system for the screw compressor motor of a two-stage heat pump system according to an embodiment of the present invention;

[0040] In the attached diagram: 1-Low-pressure stage compressor; 2-High-pressure stage compressor; 3-Oil-gas separator; 4-Pressure maintaining valve; 5-Condenser; 6-Intercooler; 7-Evaporator; 8-Low-pressure stage motor injection valve; 9-High-pressure stage motor injection valve; 10-Electric regulating valve; 11-Branch expansion valve; 12-Oil cooler; 13-Main expansion valve; 14-Check valve; 15-Ejector. Detailed Implementation

[0041] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be used interchangeably where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0043] Please see Figure 1This invention proposes a method for controlling liquid injection cooling of a screw compressor motor in a two-stage heat pump system. The two-stage heat pump system includes a low-pressure stage compressor 1 and a high-pressure stage compressor 2. The outlet of the low-pressure stage compressor 1 is connected to the inlet of the high-pressure stage compressor 2. The outlet of the high-pressure stage compressor 2 is connected to the inlet of an oil-gas separator 3. The gas outlet of the oil-gas separator 3 is connected to the inlet of a pressure maintaining valve 4. The outlet of the pressure maintaining valve 4 is connected to the inlet of a condenser 5. The outlet of the condenser 5 is connected to the main inlet of an intercooler 6. The main outlet of the intercooler 6 is connected to the inlet of a main expansion valve 13. The outlet of the main expansion valve 13 is connected to the inlet of an evaporator 7. The outlet of the evaporator 7 is connected to the inlet of the low-pressure stage compressor 1. The main outlet of the intercooler 6 is also connected to the inlets of a low-pressure stage motor liquid injection valve 8 and a high-pressure stage motor liquid injection valve 9. The outlet of the low-pressure stage motor liquid injection valve 8 is connected to the motor liquid injection port of the low-pressure stage compressor 1, and the outlet of the high-pressure stage motor liquid injection valve 9 is connected to the motor liquid injection port of the high-pressure stage compressor 2. The outlet of condenser 5 is also connected to the inlet of the gas supply branch expansion valve 11, the outlet of which is connected to the branch inlet of intercooler 6, the branch outlet of which is connected to the inlet of check valve 14, and the outlet of check valve 14 is connected to the inlet of high-pressure stage compressor 2. The oil outlet of oil-gas separator 3 is connected to the inlet of oil cooler 12, and the outlet of oil cooler 12 is connected to the oil inlet of high-pressure stage compressor 2. The outlet of condenser 5 is also connected to the inlet of oil cooler 12, the outlet of which is connected to the inlet of electric regulating valve 10, and the outlet of electric regulating valve 10 is connected to the inlet of evaporator 7. The top of condenser 5 and the bottom of evaporator 7 are connected to the inlet of ejector 15, and the outlet of ejector 15 is connected to the inlet of low-pressure stage compressor 1.

[0044] When the above-mentioned two-stage heat pump system is running, the medium-pressure gaseous refrigerant output from the outlet of the low-pressure stage compressor 1 mixes with the make-up gas from the one-way valve 14, and then flows through the high-pressure stage compressor 2 to output high-pressure gaseous refrigerant. After oil-gas separation in the oil-gas separator 3, the high-pressure liquid refrigerant releases heat and condenses in the condenser 5. The main path flows through the intercooler 6 and is subcooled by the medium-temperature, medium-pressure two-phase refrigerant in the make-up gas branch. It then flows through the main path expansion valve 13 to be throttled to low-pressure two-phase refrigerant, and then enters the evaporator 7 to absorb heat from the heat source before returning to the low-pressure stage compressor 1. The evaporator 5 releases heat and condenses into high-pressure liquid refrigerant. The make-up gas branch flows through the make-up gas branch expansion valve 11 to be throttled to medium-pressure two-phase refrigerant, and then flows through the intercooler 6 and... After heat exchange, the high-pressure liquid refrigerant in the main circuit mixes with the gaseous refrigerant at the outlet of the low-pressure stage compressor 1 through the one-way valve 14 and enters the high-pressure stage compressor 2. The high-pressure liquid refrigerant that releases heat and condenses in the condenser 5 flows through the oil cooler 12 to cool the oil and then enters the evaporator 7. The high-pressure liquid refrigerant that releases heat and becomes subcooled in the intercooler 6 flows through the low-pressure stage motor injection valve 8 and enters the motor injection port of the low-pressure stage compressor. The high-pressure liquid refrigerant that releases heat and becomes subcooled in the intercooler 6 flows through the low-pressure stage motor injection valve 9 and enters the motor injection port of the high-pressure stage compressor. The high-pressure gaseous refrigerant at the top of the condenser 5 carries the accumulated oil at the bottom of the evaporator 7 into the low-pressure stage compressor 1 through the ejector 15.

[0045] The liquid injection cooling control method for the screw compressor motor of a two-stage heat pump system proposed in this embodiment of the invention includes:

[0046] The decision to open the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 is based on the combined motor temperatures of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 of the two-stage heat pump system and the temperature difference between the motors.

[0047] The electric regulating valve 10 connected to the outlet of the oil cooler 12 is adjusted based on the difference between the injection temperature and the set injection temperature.

[0048] When the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are opened, the outlet oil temperature of the oil cooler 12 is increased to maintain the exhaust temperature at the same level as before the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 were opened. At the same time, after the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are opened, a comprehensive judgment is made based on the motor temperature and the motor temperature difference to determine whether to close the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9.

[0049] Please see Figure 2 The method for controlling the opening of the liquid injection valve of the screw compressor motor in a two-stage heat pump system, as described in this embodiment of the invention, includes:

[0050] Collect the motor temperature of low-pressure stage compressor 1 and the motor temperature of high-pressure stage compressor 2, and calculate the motor temperature difference;

[0051] Determine if the motor injection valve opens under the following conditions; otherwise, continue collecting motor temperature data:

[0052] The temperature difference between the motors of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 is less than 3℃ (exemplary value) and greater than 1℃ (exemplary value) of the first threshold temperature difference for opening the motor injection valve. At this time, the motor temperature is greater than 115℃ (exemplary value) of the first threshold temperature for opening the motor injection valve.

[0053] The temperature difference between the motors of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 is greater than the first threshold temperature difference of 3℃ (this is an example value) when the motor injection valve opens. At this time, the motor temperature is greater than the second threshold temperature of 110℃ (this is an example value) when the motor injection valve opens.

[0054] In the diagram, T1 represents the first threshold temperature difference for the motor's injection valve to open, and T2 represents the first threshold temperature difference for the motor's injection valve to open. motorup1 The first threshold temperature for opening the motor injection valve is T. motorup2 Set the second threshold temperature for the motor injection valve.

[0055] Please see Figure 3 In this embodiment of the invention, the control of the electric regulating valve of the screw compressor in a two-stage heat pump system includes:

[0056] Collect the outlet oil temperature of oil cooler 12 and the exhaust temperature of high-pressure stage compressor 2;

[0057] The opening status of the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 is collected;

[0058] If the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are closed, then the electric regulating valve 10 is subjected to PID control. The PID target value is the oil outlet temperature of the oil cooler 12, which is the set oil temperature of 60°C (this is an example value). The target adjustment value N is reset to 0.1, and the oil outlet temperature of the oil cooler 12 and the exhaust temperature of the high-pressure stage compressor 2 are collected.

[0059] If the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are open, the PID target value of the electric regulating valve 10 is the temperature of the oil outlet oil temperature of the oil cooler 12 plus the target regulation value N, which is 60.1℃ (this is an example value).

[0060] The outlet oil temperature T of oil cooler 12 oil To set the appropriate oil temperature, adjust according to the type of oil;

[0061] After opening the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9, the specific target of the electric regulating valve is: the oil cooler outlet oil temperature is T. oil+Target adjustment value N; If the exhaust temperature is still lower than the exhaust temperature before the valve is opened, the target adjustment value N will be increased appropriately; The target adjustment value N has an upper limit. When the target adjustment value N is increased to a certain value, if the exhaust temperature still cannot be increased to the same level as before the motor injection valve is opened, the target adjustment value N will be kept stable.

[0062] Continue to collect the outlet oil temperature of oil cooler 12 and the exhaust temperature of high-pressure stage compressor 2, and delay for a set time of 5 seconds (this is an example value) to ensure the adjustment effect. If the difference between the exhaust temperature of high-pressure stage compressor 2 and the exhaust temperature before opening low-pressure stage motor injection valve 8 and high-pressure stage motor injection valve 9 is less than the set value of 0.5℃ (this is an example value), then increase the target adjustment value N by 0.1 without exceeding 10. At the same time, continue to adjust the PID target value of electric regulating valve 10 to the temperature after adding the target adjustment value N to the outlet oil temperature of oil cooler 12, and repeat the subsequent operation.

[0063] If the difference between the exhaust temperature of the high-pressure stage compressor 2 and the exhaust temperature before opening the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 is greater than or equal to 0.5℃ (this is an example value), then continue to collect the opening status of the motor injection valves.

[0064] When the motor injection valve opens, the liquid refrigerant after the intercooler 6 directly enters the interstage chamber. Therefore, the suction and discharge temperatures of the high-pressure stage compressor 2 decrease, and the heating capacity of the heat pump system also decreases. At this time, appropriately increasing the oil outlet temperature of the oil cooler can compensate for the discharge temperature of the high-pressure stage compressor 2, improving the operational stability of the heat pump system.

[0065] Please see Figure 4 The method for controlling the shut-off of the liquid injection valve of the screw compressor motor in a two-stage heat pump system, as described in this embodiment of the invention, includes:

[0066] When the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are opened, the motor temperatures of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 are collected, and the motor temperature difference is calculated.

[0067] Determine if the motor injection valve closes under the following conditions; otherwise, continue collecting motor temperature data:

[0068] The temperature difference between the motors of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 is less than the motor injection valve closing threshold temperature difference of -5℃ (this is an example value), and the motor temperature is less than the first threshold temperature for closing the motor injection valve of 95℃ (this is an example value).

[0069] The temperature difference between the motors of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 is greater than the motor injection valve closing threshold temperature difference of -5℃ (this is an example value), and the motor temperature is less than the second threshold temperature of the motor injection valve closing of 90℃ (this is an example value).

[0070] In the diagram, T3 represents the temperature difference at which the motor's injection valve closes; T motorup1 T is the first closing threshold temperature of the motor injection valve. motorup2 This is the second closing threshold temperature for the motor injection valve.

[0071] In the above embodiment, before collecting the motor temperature of the low-pressure stage compressor 1 and the motor temperature of the high-pressure stage compressor 2, it is first determined whether the system is in a stable operating state; the condition for determining that the system is in a stable operating state is that the fluctuation values ​​of the suction pressure of the low-pressure stage compressor 1 and the discharge pressure of the high-pressure stage compressor 2 are less than 50 kPa / min.

[0072] The present invention provides a two-stage heat pump system screw compressor motor liquid injection cooling control method that uses motor temperature and motor temperature difference as criteria to determine whether to open the motor liquid injection valve. This allows for more precise control of motor temperature, reduces the opening time of the motor liquid injection valve, lowers fluctuations in parameters such as motor temperature, interstage pressure, exhaust temperature, and heating capacity, and improves the stability of the two-stage heat pump system.

[0073] Please see Figure 5 The present invention provides a two-stage heat pump system screw compressor motor liquid injection cooling control system, comprising:

[0074] The motor injection valve opening determination module is used to determine whether the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are open based on the motor temperature of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 and the motor temperature difference in a two-stage heat pump system.

[0075] The adjustment module is used to adjust the electric adjustment valve 10 connected to the outlet of the oil cooler 12 based on the difference between the injection temperature and the set injection temperature; and, when the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are opened, the exhaust temperature is maintained at the same level as before the low-pressure stage motor injection valve 8 and the high-pressure stage motor injection valve 9 are opened by increasing the outlet oil temperature of the oil cooler 12.

[0076] The motor injection valve closure determination module is used to determine whether to close the low-pressure motor injection valve 8 and the high-pressure motor injection valve 9 after opening the low-pressure motor injection valve 8 and the high-pressure motor injection valve 9, based on the motor temperature and the motor temperature difference.

[0077] This invention also proposes an electronic device, comprising: a memory storing at least one instruction; and a processor executing the instruction stored in the memory to implement the liquid injection cooling control method for the screw compressor motor of the two-stage heat pump system.

[0078] Another embodiment of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the liquid injection cooling control method for the screw compressor motor of the two-stage heat pump system.

[0079] For example, the instructions stored in the memory can be divided into one or more modules / units. These modules / units are stored in a computer-readable storage medium and executed by the processor to complete the liquid-jet cooling control method for the screw compressor motor of the two-stage heat pump system described in this invention. The one or more modules / units can be a series of computer-readable instruction segments capable of performing specific functions, which describe the execution process of the computer program on the server.

[0080] The electronic device may be a smartphone, laptop, PDA, or cloud server, among other computing devices. It may include, but is not limited to, a processor and memory. Those skilled in the art will understand that the electronic device may also include more or fewer components, or combinations of certain components, or different components; for example, it may also include input / output devices, network access devices, buses, etc.

[0081] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0082] The memory can be an internal storage unit of the server, such as a hard drive or RAM. Alternatively, it can be an external storage device, such as a plug-in hard drive, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, the memory can include both internal and external storage units. The memory is used to store computer-readable instructions and other programs and data required by the server. It can also be used to temporarily store data that has been output or will be output.

[0083] It should be noted that the information interaction and execution process between the above-mentioned module units are based on the same concept as the method embodiment. For details on their specific functions and technical effects, please refer to the method embodiment section. They will not be repeated here.

[0084] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0085] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of this application can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying the computer program code to a photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. Examples include USB flash drives, portable hard drives, magnetic disks, or optical disks.

[0086] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0087] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for controlling liquid injection cooling of a screw compressor motor in a two-stage heat pump system, characterized in that, The two-stage heat pump system includes a low-pressure stage compressor (1) and a high-pressure stage compressor (2). The outlet of the low-pressure stage compressor (1) is connected to the inlet of the high-pressure stage compressor (2). The outlet of the high-pressure stage compressor (2) is connected to the inlet of the oil-gas separator (3). The gas outlet of the oil-gas separator (3) is connected to the inlet of the pressure maintaining valve (4). The outlet of the pressure maintaining valve (4) is connected to the inlet of the condenser (5). The outlet of the condenser (5) is connected to the main inlet of the intercooler (6). The main outlet of the intercooler (6) is connected to the inlet of the main expansion valve (13). The outlet of the main expansion valve (13) is connected to the inlet of the evaporator (7). The outlet of the evaporator (7) is connected to the inlet of the low-pressure stage compressor (1). The main outlet of the intercooler (6) is also connected to the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (8). The inlet of the motor injection valve (9) and the outlet of the low-pressure stage motor injection valve (8) are connected to the motor injection port of the low-pressure stage compressor (1), and the outlet of the high-pressure stage motor injection valve (9) is connected to the motor injection port of the high-pressure stage compressor (2); the condenser (5) and the evaporator (7) are also connected to the inlet of the ejector (15), and the outlet of the ejector (15) is connected to the inlet of the low-pressure stage compressor (1); the oil outlet of the oil-gas separator (3) is connected to the inlet of the oil cooler (12), and the outlet of the oil cooler (12) is connected to the oil inlet of the high-pressure stage compressor (2); the outlet of the condenser (5) is also connected to the inlet of the oil cooler (12), the outlet of the oil cooler (12) is connected to the inlet of the electric regulating valve (10), and the outlet of the electric regulating valve (10) is connected to the inlet of the evaporator (7); Control methods include: Based on the motor temperatures of the low-pressure stage compressor (1) and the high-pressure stage compressor (2) of the two-stage heat pump system, as well as the difference between the motor temperatures collected in the previous two tests, it is determined whether to open the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9). The electric regulating valve (10) connected to the outlet of the oil cooler (12) is adjusted based on the difference between the injection temperature and the set injection temperature. After the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are opened, the exhaust temperature is maintained at the same level as before the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are opened by increasing the outlet oil temperature of the oil cooler (12); at the same time, after the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are opened, the motor temperature is collected again, and the motor temperature and the difference between the two collected motor temperatures are used to determine whether to close the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9). Collect the motor temperature of the low-pressure stage compressor (1) and the motor temperature of the high-pressure stage compressor (2), and calculate the difference between the two collected motor temperatures. Determine if the low-pressure stage motor injection valve opens under the following conditions; otherwise, continue collecting motor temperature data: The difference between the motor temperature collected before and after the low-pressure stage compressor (1) is less than the first threshold temperature difference for opening the low-pressure stage motor injection valve and greater than the second threshold temperature difference for opening the low-pressure stage motor injection valve. At this time, the motor temperature of the low-pressure stage compressor is greater than the first threshold temperature for opening the low-pressure stage motor injection valve. The difference in motor temperature collected before and after the low-pressure stage compressor (1) is greater than the first threshold temperature difference for opening the low-pressure stage motor injection valve. At this time, the motor temperature of the low-pressure stage compressor is greater than the second threshold temperature for opening the low-pressure stage motor injection valve. Determine if the high-pressure stage motor injection valve opens under the following conditions; otherwise, continue collecting motor temperature data: The difference in motor temperature collected before and after the high-pressure stage compressor (2) is less than the first threshold temperature difference for opening the high-pressure stage motor injection valve and greater than the second threshold temperature difference for opening the high-pressure stage motor injection valve. At this time, the motor temperature of the high-pressure stage compressor is greater than the first threshold temperature for opening the high-pressure stage motor injection valve. The difference between the motor temperature collected before and after the high-pressure stage compressor (2) is greater than the first threshold temperature difference for opening the high-pressure stage motor injection valve. At this time, the motor temperature of the high-pressure stage compressor is greater than the second threshold temperature for opening the high-pressure stage motor injection valve. The method also includes: after the system is in a stable operating state, collecting the outlet oil temperature of the oil cooler (12) and the exhaust temperature of the high-pressure stage compressor (2); The opening status of the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) is collected; If the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are opened, the electric regulating valve (10) is subjected to PID control. The PID target value is the oil outlet temperature of the oil cooler (12) plus the target adjustment value. The oil outlet temperature of the oil cooler (12) and the exhaust temperature of the high-pressure stage compressor (2) are collected and delayed for a set time. If the difference between the exhaust temperature of the high-pressure stage compressor (2) and the exhaust temperature before the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are less than the set value, the target adjustment value is increased. At the same time, the PID target value of the electric regulating valve (10) is adjusted to the oil outlet temperature of the oil cooler (12) plus the target adjustment value. The subsequent operation is repeated.

2. The liquid injection cooling control method for the screw compressor motor of a two-stage heat pump system according to claim 1, characterized in that: When the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are opened, the motor temperatures of the low-pressure stage compressor (1) and the high-pressure stage compressor (2) are collected, and the difference between the motor temperatures collected before and after the two collections is calculated. Determine if the low-pressure stage motor injection valve closes under the following conditions; otherwise, continue collecting motor temperature data: The difference in motor temperature collected before and after the low-pressure stage compressor (1) is less than the temperature difference of the low-pressure stage motor injection valve closing threshold. At this time, the motor temperature of the low-pressure stage compressor is less than the first threshold temperature of the low-pressure stage motor injection valve closing. The difference between the motor temperature collected before and after the low-pressure stage compressor (1) is greater than the temperature difference of the low-pressure stage motor injection valve closing threshold. At this time, the motor temperature of the low-pressure stage compressor is less than the second threshold temperature of the low-pressure stage motor injection valve closing. Determine if the high-pressure stage motor injection valve closes under the following conditions; otherwise, continue collecting motor temperature data: The difference in motor temperature collected before and after the high-pressure stage compressor (2) is less than the temperature difference of the high-pressure stage motor injection valve closing threshold. At this time, the motor temperature of the high-pressure stage compressor is less than the first threshold temperature of the high-pressure stage motor injection valve closing. The difference between the motor temperature collected before and after the high-pressure stage compressor (2) is greater than the temperature difference of the high-pressure stage motor injection valve closing threshold. At this time, the motor temperature of the high-pressure stage compressor is less than the second threshold temperature of the high-pressure stage motor injection valve closing.

3. The liquid injection cooling control method for the screw compressor motor of a two-stage heat pump system according to claim 1 or 2, characterized in that: Before collecting the motor temperature of the low-pressure stage compressor (1) and the motor temperature of the high-pressure stage compressor (2), it is first determined whether the system is in a stable operating state. The conditions for determining that the system is in a stable operating state are met: the fluctuation values ​​of the suction pressure of the low-pressure stage compressor (1) and the discharge pressure of the high-pressure stage compressor (2) are less than 50 kPa / min.

4. The liquid injection cooling control method for the screw compressor motor of a two-stage heat pump system according to claim 1, characterized in that, The outlet of the condenser (5) is also connected to the inlet of the gas supply branch expansion valve (11), the outlet of the gas supply branch expansion valve (11) is connected to the branch inlet of the intercooler (6), the branch outlet of the intercooler (6) is connected to the inlet of the check valve (14), and the outlet of the check valve (14) is connected to the inlet of the high-pressure stage compressor (2).

5. A liquid-jet cooling control system for a screw compressor motor in a two-stage heat pump system, implementing the liquid-jet cooling control method for a screw compressor motor in a two-stage heat pump system as described in any one of claims 1 to 4, characterized in that, include: The motor injection valve opening judgment module is used to comprehensively judge whether to open the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) based on the motor temperature of the low-pressure stage compressor (1) and the high-pressure stage compressor (2) of the two-stage heat pump system and the difference in motor temperature collected before and after. The adjustment module is used to adjust the electric adjustment valve (10) connected to the outlet of the oil cooler (12) based on the difference between the injection temperature and the set injection temperature; and, when the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are opened, the exhaust temperature is maintained at the same level as before the low-pressure stage motor injection valve (8) and the high-pressure stage motor injection valve (9) are opened by increasing the outlet oil temperature of the oil cooler (12); The motor injection valve closing judgment module is used to determine whether to close the low-pressure motor injection valve (8) and the high-pressure motor injection valve (9) based on the motor temperature and the motor temperature difference after the low-pressure motor injection valve (8) and the high-pressure motor injection valve (9) are opened.

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