A two-stage compression heat pump system, load adding and subtracting control method and control system

Abstract

A two-stage compression heat pump system, a load adding and reducing control method and a control system, the heat pump system comprising a low-pressure stage compressor and a high-pressure stage compressor, the rotation speeds of the low-pressure stage compressor and the high-pressure stage compressor being simultaneously adjusted by a controller to regulate the condenser outlet water temperature; the rotation speed of the high-pressure stage compressor is adjusted alone to regulate the inter-stage pressure between the low-pressure stage compressor and the high-pressure stage compressor. The actual condenser outlet water temperature, the low-pressure stage compressor rotation speed and the high-pressure stage compressor rotation speed are collected; the low-pressure stage compressor rotation speed is adjusted based on the difference between the set condenser outlet water temperature and the actual condenser outlet water temperature, and the high-pressure stage compressor rotation speed is adjusted proportionally; the low-pressure stage suction pressure, the high-pressure stage discharge pressure and the inter-stage pressure are collected; and the high-pressure stage compressor rotation speed is adjusted based on the difference between the optimal inter-stage pressure and the actual inter-stage pressure. The application improves the energy efficiency and safety of the heat pump system.

Description

Technical Field

[0001] This invention belongs to the field of heat pump technology, and relates to a two-stage compression heat pump system, a load control method, and a control system. Background Technology

[0002] For the same heating capacity, heat pumps consume only one-fifth the power of traditional equipment, making them widely used in various fields. In some applications, heat pump systems need to operate under conditions of large temperature differences. Due to these large temperature differences, the heating capacity and energy efficiency of traditional single-stage compression heat pump systems will decrease, and the compressor's exhaust temperature will also be higher.

[0003] The principle of two-stage compression technology is to divide a compression process into two stages, one with high pressure and the other with low pressure, to reduce the pressure difference between each stage. By reducing the pressure difference and using interstage economizers for gas injection, two-stage compression technology can effectively improve the heating capacity and energy efficiency of heat pump systems under conditions of large temperature differences.

[0004] To improve the energy efficiency and regulation capabilities of compressors in heat pump systems, variable frequency motors are increasingly being applied. In a two-stage compression heat pump system equipped with dual variable frequency motors, the compressor speeds of both the high and low pressure stages can be changed, thus controlling the condenser outlet water temperature by adjusting the compressor speed. However, changing the speed ratio of the high and low pressure stages also alters the interstage pressure. Interstage pressure is a crucial operating parameter of a two-stage compression heat pump system, affecting its energy efficiency and oil supply capacity. The optimal interstage pressure, resulting in the lowest energy consumption, varies under different operating conditions. Therefore, to further improve the energy efficiency of a two-stage compression heat pump system, in addition to adjusting the condenser outlet water temperature, the interstage pressure also needs to be regulated. Summary of the Invention

[0005] The purpose of this invention is to address the problems in the prior art by providing a two-stage compression heat pump system, a load control method, and a control system, so that the heat pump system has the ability to regulate both the condenser outlet water temperature and the interstage pressure, and ensures that the heat pump system is more energy-efficient and safer while maintaining its regulatory capabilities.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A two-stage compression heat pump system includes a low-pressure stage compressor and a high-pressure stage compressor. A controller simultaneously adjusts the speeds of the low-pressure stage compressor and the high-pressure stage compressor to regulate the condenser outlet water temperature. The controller also individually adjusts the speed of the high-pressure stage compressor to regulate the interstage pressure between the low-pressure stage compressor and the high-pressure stage compressor.

[0008] As a preferred embodiment, the low-pressure stage compressor and the high-pressure stage compressor are each controlled by their respective variable frequency motors. The first PID controller receives real-time condenser outlet water temperature data and simultaneously adjusts the speeds of the low-pressure stage compressor and the high-pressure stage compressor. The second PID controller receives real-time interstage pressure data between the low-pressure stage compressor and the high-pressure stage compressor and separately adjusts the speed of the high-pressure stage compressor.

[0009] As a preferred embodiment, 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 the oil-gas separator, the gas outlet of the oil-gas separator is connected to the inlet of the pressure maintaining valve, and the outlet of the pressure maintaining valve is connected to the inlet of the condenser.

[0010] As a preferred embodiment, the oil outlet of the oil-gas separator is connected to the inlet of the oil cooler, the outlet of the oil cooler is connected to the inlet of the oil quantity control valve, and the outlet of the oil quantity control valve is connected to the oil injection port of the high-pressure stage compressor.

[0011] As a preferred embodiment, the outlet of the condenser is connected to the inlet of the first passage of the intercooler via the main line, the outlet of the first passage of the intercooler is connected to the inlet of the main line expansion valve, the outlet of the main line 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.

[0012] As a preferred embodiment, the outlet of the condenser is connected to the inlet of the gas supply branch expansion valve via a gas supply branch, the outlet of the gas supply branch expansion valve is connected to the inlet of the second passage of the intercooler, the outlet of the second passage of the intercooler is connected to the inlet of a one-way valve, and the outlet of the one-way valve is connected to the outlet of the low-pressure stage compressor.

[0013] A method for load on / off control of a two-stage compression heat pump system includes the following steps:

[0014] Set the target outlet water temperature for the condenser;

[0015] Collect the actual outlet water temperature of the condenser, the speed of the low-pressure stage compressor, and the speed of the high-pressure stage compressor;

[0016] Based on the difference between the target outlet water temperature of the condenser and the actual outlet water temperature of the condenser, the speed of the low-pressure stage compressor is adjusted, and the speed of the high-pressure stage compressor is adjusted proportionally at the same time.

[0017] The system collects the suction pressure of the low-pressure stage compressor, the discharge pressure of the high-pressure stage compressor, and the interstage pressure. Based on the difference between the optimal interstage pressure calculated from the suction and discharge pressures and the actual interstage pressure, the speed of the high-pressure stage compressor is adjusted.

[0018] As a preferred embodiment, the calculation expression for the optimal interstage pressure is as follows:

[0019]

[0020] In the formula, C is the correction coefficient; P in P is the suction pressure of the low-pressure stage compressor. out This refers to the discharge pressure of the high-pressure stage compressor.

[0021] As a preferred approach, the actual outlet water temperature of the condenser, the speed of the low-pressure stage compressor, and the speed of the high-pressure stage compressor are collected only after the system is determined to be in a stable operating state. The conditions for determining that the system is in a stable operating state are met as follows:

[0022] The fluctuation values ​​of the suction pressure of the low-pressure stage compressor and the discharge pressure of the high-pressure stage compressor are less than 50 kPa / min, and the fluctuation value of the outlet water temperature of the condenser is less than 5℃ / min;

[0023] In the step of adjusting the speed of the low-pressure stage compressor and simultaneously adjusting the speed of the high-pressure stage compressor proportionally, the proportion is the speed ratio between the low-pressure stage compressor and the high-pressure stage compressor before adjustment; and if the speed adjustment value of the low-pressure stage compressor is greater than a set threshold, the speed adjustment value of the low-pressure stage compressor is limited to the set threshold.

[0024] A load on / off control system for the two-stage compression heat pump system, comprising:

[0025] The monitoring module is used to obtain the compressor suction and discharge pressure in the heat pump system and determine whether the system is stable.

[0026] The control module is used to set the target outlet water temperature of the condenser; collect the actual outlet water temperature of the condenser, the speed of the low-pressure stage compressor, and the speed of the high-pressure stage compressor; adjust the speed of the low-pressure stage compressor based on the difference between the target outlet water temperature and the actual outlet water temperature of the condenser, and adjust the speed of the high-pressure stage compressor proportionally; collect the suction pressure of the low-pressure stage compressor, the discharge pressure of the high-pressure stage compressor, and the interstage pressure, and adjust the speed of the high-pressure stage compressor based on the difference between the optimal interstage pressure calculated from the suction and discharge pressures and the actual interstage pressure.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] By regulating the condenser outlet water temperature of the heat pump system through the speeds of the low-pressure and high-pressure compressors, this invention achieves high control precision, avoiding energy losses caused by frequent start-up and shutdown control, and eliminating the need for additional mechanical components in slide valve control. This invention simultaneously regulates the speeds of both high- and low-pressure compressors via a controller, achieving the same refrigerant mass flow rate variation with smaller compressor speed adjustments. This allows the motor to operate closer to its design operating point, resulting in higher efficiency. Furthermore, the invention minimizes interstage pressure variations in the two-stage compression heat pump system, preventing excessive pressure increases during adjustment that could lead to insufficient oil supply and improving the safety of the heat pump system. Finally, by regulating the interstage pressure of the heat pump system through the high-pressure compressor speed, this invention maintains the interstage pressure at its optimal level, thereby improving the energy efficiency of the heat pump system.

[0029] Furthermore, the load control method for the two-stage compression heat pump system of the present invention determines whether the system is in a stable operating state, thereby avoiding control failure caused by unstable heat pump system parameters during startup.

[0030] Furthermore, the load control method for the two-stage compression heat pump system of the present invention limits the speed adjustment value of the low-pressure stage compressor during the adjustment process to avoid excessive interstage pressure and insufficient oil supply. Attached Figure Description

[0031] Figure 1 A schematic diagram of the structure of the two-stage compression heat pump system according to an embodiment of the present invention;

[0032] Figure 2 Flowchart of the load loading and unloading control method for a two-stage compression heat pump system according to an embodiment of the present invention;

[0033] Figure 3 A structural block diagram of the load loading and unloading control system of the two-stage compression heat pump system according to an embodiment of the present invention;

[0034] 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-Check valve; 9-Oil quantity control valve; 10-Main gas branch expansion valve; 11-Main expansion valve; 12-Oil cooler; 13-First PID controller; 14-Second PID controller. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] Please see Figure 1 The two-stage compression heat pump system of this invention 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 via a main line to the inlet of the first passage of the intercooler 6. The outlet of the first passage of the intercooler 6 is connected to the inlet of the main line expansion valve 11. The outlet of the main line expansion valve 11 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 outlet of the condenser 5 is connected via a supplementary... The gas branch is connected to the inlet of the gas supply branch expansion valve 10, the outlet of the gas supply branch expansion valve 10 is connected to the inlet of the second passage of the intercooler 6, the outlet of the second passage of the intercooler 6 is connected to the inlet of the check valve 8, and the outlet of the check valve 8 is connected to the outlet 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, the outlet of the oil cooler 12 is connected to the inlet of the oil quantity control valve 9, and the outlet of the oil quantity control valve 9 is connected to the oil injection port of the high-pressure stage compressor 2; the first PID controller 13 controls the speed of the high and low-pressure stage compressors by real-time acquisition of the condenser outlet water temperature; the second PID controller 14 controls the speed of the high-pressure stage compressor 2 by real-time acquisition of the interstage pressure.

[0038] In this embodiment of the invention, when the above-mentioned two-stage compression heat pump system is running, the medium-pressure gaseous refrigerant output from the outlet of the low-pressure stage compressor 1 is mixed with the gas supplied by the one-way valve 8 and flows through the high-pressure stage compressor 2 to output high-pressure gaseous refrigerant. After oil-gas separation in the oil-gas separator 3, it releases heat and condenses into high-pressure liquid refrigerant in the condenser 5. The main path flows through the intercooler 6 and is subcooled by the medium-temperature and medium-pressure two-phase refrigerant in the gas supply branch. It then flows through the main path expansion valve 11 and is throttled to low-pressure two-phase refrigerant. After entering the evaporator 7 to absorb heat from the heat source, it returns to the low-pressure stage compressor 1. The condenser 5 releases heat and condenses into high-pressure liquid refrigerant. The gas supply branch flows through the gas supply branch expansion valve 10 and is throttled to medium-pressure two-phase refrigerant. After exchanging heat with the high-pressure liquid refrigerant in the main path through the intercooler 6, it passes through the one-way valve 8 and mixes with the gaseous refrigerant at the outlet of the low-pressure stage compressor 1 before entering the high-pressure stage compressor 2.

[0039] Based on the above-mentioned two-stage compression heat pump system, this invention discloses a load control method for a two-stage compression heat pump system, which adjusts the speed of the high and low pressure stage compressors according to real-time collected parameters to change the condenser outlet temperature and interstage pressure of the heat pump system.

[0040] Please see Figure 2 The load control method for a two-stage compression heat pump system according to an embodiment of the present invention includes the following steps:

[0041] Set the target outlet water temperature for condenser 5;

[0042] Collect the actual outlet water temperature of condenser 5, the speed of low-pressure stage compressor 1, and the speed of high-pressure stage compressor 2;

[0043] Based on the difference between the target outlet water temperature of condenser 5 and the actual outlet water temperature of condenser 5, the speed of low-pressure stage compressor 1 is adjusted, and the speed of high-pressure stage compressor 2 is adjusted proportionally at the same time.

[0044] The suction pressure of low-pressure stage compressor 1, the discharge pressure of high-pressure stage compressor 2, and the interstage pressure are collected. Based on the difference between the optimal interstage pressure calculated from the suction and discharge pressures and the actual interstage pressure, the speed of high-pressure stage compressor 2 is adjusted.

[0045] The formula for calculating the optimal interstage pressure is as follows:

[0046]

[0047] In the formula, C is the correction coefficient; P in P is the suction pressure of the low-pressure stage compressor 1; out This refers to the discharge pressure of the high-pressure stage compressor 2.

[0048] Before collecting the actual outlet water temperature of condenser 5, the speed of low-pressure stage compressor 1, and the speed of high-pressure stage compressor 2, it is necessary to determine whether the system is in a stable operating state. At startup, the parameters within the system are not stable, which may lead to incorrect judgments regarding load increase / decrease requirements. Therefore, it is necessary to run the system for a period of time before implementing load increase / decrease control. In this embodiment, the stability of the system is determined by acquiring the compressor suction and discharge pressures and the condenser outlet water temperature in the heat pump system: the fluctuation values ​​of the suction pressure of low-pressure stage compressor 1 and the discharge pressure of high-pressure stage compressor 2 are less than 50 kPa / min, and the fluctuation value of the outlet water temperature of condenser 5 is less than 5℃ / min.

[0049] The steps of collecting the actual outlet water temperature of condenser 5, the speed of low-pressure stage compressor 1, and the speed of high-pressure stage compressor 2 are implemented after the fluctuations in compressor suction and discharge pressures and the fluctuations in condenser outlet water temperature in the heat pump system are less than the set values.

[0050] In the step of adjusting the speed of the low-pressure stage compressor 1 and simultaneously adjusting the speed of the high-pressure stage compressor 2 proportionally, the ratio is the ratio of the speeds of the high-pressure and low-pressure stage compressors before adjustment; and if the speed adjustment value of the low-pressure stage compressor 1 is greater than the set threshold, the speed adjustment value of the low-pressure stage compressor 1 will be limited to the set threshold.

[0051] Based on the difference between the target outlet water temperature of condenser 5 and the actual outlet water temperature of condenser 5, the speed of low-pressure stage compressor 1 is adjusted, and the speed of high-pressure stage compressor 2 is adjusted proportionally. After a first preset time, the speed of high-pressure stage compressor 2 is adjusted again based on the difference between the optimal interstage pressure calculated from the suction and discharge pressures and the actual interstage pressure. Here, the first preset time can be a 10-second delay (this value is only an example value) until the pressure at each point is relatively stable.

[0052] The first PID controller controls the condenser outlet temperature of the heat pump system by adjusting the speeds of the low-pressure and high-pressure compressors. The second PID controller controls the interstage pressure by adjusting the speed of the high-pressure compressor. When the set condenser outlet water temperature is higher than the actual condenser outlet water temperature, according to the PID control characteristics, the first PID controller increases the speed of the low-pressure compressor and increases the speed of the high-pressure compressor according to the original high-low pressure compressor speed ratio. This increases the refrigerant mass flow rate in the heat pump system, thereby increasing the heating capacity of the heat pump system and raising the actual condenser outlet temperature. When the set condenser outlet water temperature is lower than the actual condenser outlet water temperature, according to the PID control characteristics, the first PID controller decreases the speed of the low-pressure compressor and decreases the speed of the high-pressure compressor according to the original high-low pressure compressor speed ratio. This decreases the refrigerant mass flow rate in the heat pump system, thereby reducing the heating capacity of the heat pump system and lowering the actual condenser outlet temperature. Furthermore, when actually adjusting the compressor speed, it is determined whether the adjusted low-pressure compressor speed exceeds a set threshold of 250 rpm (this value is only an example). If the adjusted low-pressure compressor speed exceeds the set threshold, the compressor speed adjustment is limited to the set threshold. If the low-pressure stage compressor speed adjustment is less than the set threshold, the compressor speed adjustment value will remain unchanged.

[0053] Based on the difference between the optimal interstage pressure calculated from the intake and exhaust pressures and the actual interstage pressure, the speed of the high-pressure stage compressor 2 is adjusted, and after a second preset time, the above control steps are repeated. When the actual interstage pressure is greater than the optimal interstage pressure, the second PID controller increases the speed of the high-pressure stage compressor according to the PID control characteristics. When the actual interstage pressure is less than the optimal interstage pressure, the second PID controller decreases the speed of the high-pressure stage compressor according to the PID control characteristics.

[0054] Heat pump systems using variable frequency motors typically employ variable frequency control (VFD) for load loading and unloading, which avoids some drawbacks of traditional methods. However, in a two-stage compression heat pump system, variations in the compressor speeds of the high and low pressure stages lead to changes in interstage pressure, which affects the system's energy efficiency and fuel supply. Therefore, adjusting the interstage pressure simultaneously with load loading and unloading can further leverage the advantages of VFD control and improve the system's energy efficiency and safety.

[0055] The control method provided by this invention divides the control steps into two parts:

[0056] The first part involves adjusting the outlet water temperature of condenser 5 in the heat pump system, which corresponds to the heating capacity, by regulating the speeds of the high- and low-pressure stage compressors. Adjusting the speed of the low-pressure stage compressor 1 and, according to the original high- and low-pressure stage compressor speed ratio, adjusting the speed of the high-pressure stage compressor 2 increases the refrigerant mass flow rate of the heat pump system while maintaining minimal interstage pressure changes. Simultaneous adjustment of the high- and low-pressure stage speeds achieves the same mass flow rate change with a smaller compressor speed adjustment, thus allowing the motor to operate closer to its design operating point and resulting in higher efficiency. Minimal interstage pressure changes also prevent excessive pressure increases during adjustment, which could lead to insufficient oil supply.

[0057] The second part involves regulating the interstage pressure by adjusting the speed of the high-pressure stage compressor 2. The first part simultaneously adjusts the speeds of both the high-pressure and low-pressure stage compressors; however, the leakage rate of the compressor varies at different speeds, thus causing changes in the interstage pressure. Furthermore, the optimal interstage pressure also changes due to variations in the compressor's suction and discharge pressures. In summary, by adjusting the speed of the high-pressure stage compressor 2 based on the difference between the actual and optimal interstage pressures, compressor power consumption can be further reduced, improving the energy efficiency of the heat pump system.

[0058] Please see Figure 3 The present invention also proposes a load on / off control system for a two-stage compression heat pump system, comprising:

[0059] The monitoring module is used to obtain the compressor suction and discharge pressure in the heat pump system and determine whether the system is stable.

[0060] The control module is used to set the target outlet water temperature of condenser 5; collect the actual outlet water temperature of condenser 5, the speed of low-pressure stage compressor 1, and the speed of high-pressure stage compressor 2; adjust the speed of low-pressure stage compressor 1 based on the difference between the target outlet water temperature and the actual outlet water temperature of condenser 5, and adjust the speed of high-pressure stage compressor 2 proportionally; collect the suction pressure of low-pressure stage compressor 1, the discharge pressure of high-pressure stage compressor 2, and the interstage pressure, and adjust the speed of high-pressure stage compressor 2 based on the difference between the optimal interstage pressure calculated from the suction and discharge pressures and the actual interstage pressure.

[0061] The formula for calculating the optimal interstage pressure is as follows:

[0062]

[0063] In the formula, C is the correction coefficient; P in P is the suction pressure of the low-pressure stage compressor 1; out This refers to the discharge pressure of the high-pressure stage compressor 2.

[0064] Furthermore, the step of setting the target outlet water temperature of the condenser 5 by the control module is implemented after the fluctuations in the compressor suction and discharge pressures and the fluctuations in the condenser outlet water temperature in the heat pump system of the monitoring module are less than the set values.

[0065] Furthermore, in the step of adjusting the speed of the low-pressure stage compressor 1 and simultaneously adjusting the speed of the high-pressure stage compressor 2 proportionally, the ratio is the speed ratio between the low-pressure stage compressor 1 and the high-pressure stage compressor 2 before adjustment.

[0066] Furthermore, in the step of adjusting the speed of the low-pressure stage compressor 1 and simultaneously adjusting the speed of the high-pressure stage compressor 2 proportionally, if the speed adjustment value of the low-pressure stage compressor 1 is greater than the set threshold, the speed adjustment value of the low-pressure stage compressor 1 is limited to the set threshold.

[0067] Furthermore, the control module adjusts the speed of the low-pressure stage compressor 1 based on the difference between the target outlet water temperature of the condenser 5 and the actual outlet water temperature of the condenser 5, and adjusts the speed of the high-pressure stage compressor 2 proportionally. After a first preset time, the module collects the suction pressure of the low-pressure stage compressor 1, the discharge pressure of the high-pressure stage compressor 2, and the interstage pressure. Based on the difference between the optimal interstage pressure calculated from the suction and discharge pressures and the actual interstage pressure, the module adjusts the speed of the high-pressure stage compressor 2.

[0068] Furthermore, the control module adjusts the speed of the low-pressure stage compressor 1 and the high-pressure stage compressor 2 through the first PID controller 13 to control the outlet temperature of the heat pump system condenser 5, and adjusts the speed of the high-pressure stage compressor 2 through the second PID controller 14 to control the interstage pressure between the low-pressure stage compressor 1 and the high-pressure stage compressor 2.

[0069] Furthermore, after the control module calculates the difference between the optimal interstage pressure and the actual interstage pressure based on the intake and exhaust pressures, it adjusts the speed of the high-pressure stage compressor 2 and repeats the steps in the control module after a second preset time.

[0070] This invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a nonvolatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the load on / off control method for the two-stage compression heat pump system in the above embodiments.

[0071] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0072] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0073] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The function specified in one or more boxes.

[0074] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A two-stage compression heat pump system, characterized in that: It includes a low-pressure stage compressor (1) and a high-pressure stage compressor (2). The controller simultaneously adjusts the speed of the low-pressure stage compressor (1) and the high-pressure stage compressor (2) to adjust the outlet water temperature of the condenser (5). The controller separately adjusts the speed of the high-pressure stage compressor (2) to adjust the interstage pressure between the low-pressure stage compressor (1) and the high-pressure stage compressor (2). The low-pressure stage compressor (1) and the high-pressure stage compressor (2) are controlled by their respective variable frequency motors. The first PID controller (13) receives the real-time collected water temperature data of the condenser (5) and simultaneously adjusts the speed of the low-pressure stage compressor (1) and the high-pressure stage compressor (2). The second PID controller (14) receives the real-time collected interstage pressure data between the low-pressure stage compressor (1) and the high-pressure stage compressor (2) and adjusts the speed of the high-pressure stage compressor (2) separately. The two-stage compression heat pump system sets the target outlet water temperature of the condenser (5); and collects the actual outlet water temperature of the condenser (5), the speed of the low-pressure stage compressor (1), and the speed of the high-pressure stage compressor (2). Based on the difference between the target outlet water temperature of the condenser (5) and the actual outlet water temperature of the condenser (5), the speed of the low-pressure stage compressor (1) is adjusted, and the speed of the high-pressure stage compressor (2) is adjusted proportionally. The suction pressure of the low-pressure stage compressor (1), the discharge pressure of the high-pressure stage compressor (2) and the interstage pressure are collected. Based on the difference between the optimal interstage pressure calculated by the suction and discharge pressure and the actual interstage pressure, the speed of the high-pressure stage compressor (2) is adjusted. 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), and 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 inlet of the first passage of the intercooler (6) via the main line. The outlet of the first passage of the intercooler (6) is connected to the inlet of the main line expansion valve (11). The outlet of the main line expansion valve (11) 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 outlet of the condenser (5) is connected to the inlet of the gas supply branch expansion valve (10) via the gas supply branch. The outlet of the gas supply branch expansion valve (10) is connected to the inlet of the second passage of the intercooler (6). The outlet of the second passage of the intercooler (6) is connected to the inlet of the check valve (8). The outlet of the check valve (8) is connected to the outlet of the low-pressure stage compressor (1).

2. The two-stage compression heat pump system according to claim 1, characterized in that: The oil outlet of the oil-gas separator (3) is connected to the inlet of the oil cooler (12), the outlet of the oil cooler (12) is connected to the inlet of the oil quantity control valve (9), and the outlet of the oil quantity control valve (9) is connected to the oil injection port of the high-pressure stage compressor (2).

3. The two-stage compression heat pump system according to claim 1, characterized in that, The formula for calculating the optimal interstage pressure is as follows: ； In the formula, This is a correction factor; The suction pressure of the low-pressure stage compressor (1); The discharge pressure of the high-pressure stage compressor (2).

4. The two-stage compression heat pump system according to claim 1, characterized in that, First, determine that the system is in a stable operating state before collecting the actual outlet water temperature of the condenser (5), the speed of the low-pressure stage compressor (1), and the speed of the high-pressure stage compressor (2). The conditions for determining that the system is in a stable operating state are: 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, and the fluctuation value of the outlet water temperature of the condenser (5) is less than 5 ℃ / min. In the step of adjusting the speed of the low-pressure stage compressor (1) and adjusting the speed of the high-pressure stage compressor (2) proportionally, the ratio is the speed ratio of the low-pressure stage compressor (1) and the high-pressure stage compressor (2) before adjustment; Furthermore, if the speed adjustment value of the low-pressure stage compressor (1) is greater than the set threshold, the speed adjustment value of the low-pressure stage compressor (1) is limited to the set threshold.

5. A load on / off control system for a two-stage compression heat pump system as described in claim 1, characterized in that, include: The monitoring module is used to obtain the compressor suction and discharge pressure in the heat pump system and determine whether the system is stable. The control module is used to set the target outlet water temperature of the condenser (5); Collect the actual outlet water temperature of the condenser (5), the speed of the low-pressure stage compressor (1), and the speed of the high-pressure stage compressor (2); Based on the difference between the target outlet water temperature of the condenser (5) and the actual outlet water temperature of the condenser (5), the speed of the low-pressure stage compressor (1) is adjusted, and the speed of the high-pressure stage compressor (2) is adjusted proportionally. The suction pressure of the low-pressure stage compressor (1), the discharge pressure of the high-pressure stage compressor (2) and the interstage pressure are collected. Based on the difference between the optimal interstage pressure calculated by the suction and discharge pressure and the actual interstage pressure, the speed of the high-pressure stage compressor (2) is adjusted.

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