Two-stage compression heat pump system, control method and control device

Abstract

The invention relates to the technical field of heat pumps, and discloses a two-stage compression heat pump system, a control method and a control device. The two-stage compression heat pump system comprises a high-pressure-stage compressor, a low-pressure-stage compressor, a first one-way valve, an economizer and a third throttling valve, wherein the high-pressure-stage compressor and the low-pressure-stage compressor are inverter compressors; one end of a second heat exchange tube of the economizer communicates with the condenser through a second throttle valve, and the other end of the second heat exchange tube communicates with an air outlet of the low-pressure-stage compressor through a second one-way valve; one end of the third throttle valve communicates with an inlet of the second one-way valve, and the other end communicates with an air supply port of the low-pressure-stage compressor. By arranging the two-stage frequency conversion compressor, the regulation and control flexibility of the heat pump system is improved; the first one-way valve is connected beside the high-pressure-stage compressor in parallel, single-stage operation or double-stage operation of the system can be switched according to the load, the environment working condition and the dynamic operation working condition of the system, and the heat pump system can be switched among different operation modes in cooperation with opening and closing of the valve body.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pumps, and in particular, to a two-stage compression heat pump system, a control method and a control device therefor. Background Art

[0002] The high-temperature hot water used in the low-temperature regions in the north has a relatively high temperature. Ordinary heat pump systems cannot provide high-temperature hot water under low-temperature working conditions. The technology of using a two-stage compression heat pump system to provide high-temperature hot water is very common. However, the currently commonly used two-stage compression heat pump systems have low flexibility in adjustment except for large temperature difference working conditions. For application scenarios that require heating throughout the year, the operating temperature range of the two-stage compression heat pump system spans extremely large, and the system operates from -40°C to 38°C. However, the two-stage compression heat pump system lacks a control strategy for adaptively adjusting the system operation according to different environmental working conditions. Especially under small temperature difference working conditions, the energy efficiency is very low, and the switching point setting is often unreasonable, resulting in a large amount of energy waste. For example, when manufacturing 40°C hot water under the working condition of an outdoor environment of 25°C, two-stage compression is still carried out under the working condition of a small temperature difference between the evaporation temperature and the condensation temperature, and the exergy loss is large and the energy efficiency is very low. Summary of the Invention

[0003] The present invention provides a two-stage compression heat pump system, a control method and a control device therefor. The problem to be solved is that the two-stage compression heat pump system in the prior art has low flexibility in adjustment, still performs two-stage compression under small temperature difference working conditions, has a large exergy loss and low energy efficiency.

[0004] The first aspect of the present invention provides a two-stage compression heat pump system, including: A high-pressure stage compressor and a low-pressure stage compressor, both of which are variable-frequency compressors; the intake port of the high-pressure stage compressor is communicated with the outlet port of the low-pressure stage compressor; A first check valve, which is connected in parallel with the high-pressure stage compressor; An economizer, in which a first heat exchange tube and a second heat exchange tube are provided; one end of the first heat exchange tube is communicated with the outlet port of the high-pressure stage compressor through a condenser, and the other end of the first heat exchange tube is communicated with the intake port of the low-pressure stage compressor through an evaporator; one end of the second heat exchange tube is communicated with the condenser through a second throttle valve, and the other end is communicated with the outlet port of the low-pressure stage compressor through a second check valve; A third throttle valve, one end of which is communicated with the inlet of the second check valve, and the other end of which is communicated with the gas supplement port of the low-pressure stage compressor.

[0005] According to the two-stage compression heat pump system provided by the present invention, it further includes: Four-way valve, wherein the D pipe of the four-way valve is communicated with the air outlet of the high-stage compressor, the S pipe of the four-way valve is communicated with the air inlet of the low-stage compressor, the E pipe of the four-way valve is communicated with the evaporator, and the C pipe of the four-way valve is communicated with the condenser.

[0006] The second aspect of the present invention provides a control method for a two-stage compression heat pump system. The operating modes of the two-stage compression heat pump system include a two-stage non-increasing enthalpy mode, a two-stage increasing enthalpy mode, a single-stage non-increasing enthalpy mode, and a single-stage increasing enthalpy mode. The control method includes: Obtain the set discharge pressure of the high-stage compressor and the set suction pressure of the low-stage compressor. Determine the target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure. Determine the operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system.

[0007] According to the control method for a two-stage compression heat pump system provided by the present invention, the step of determining the operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system includes: Determine the first function of the ambient temperature according to the ambient temperature, the constant m, and the constant n. Determine the second function of the high and low pressure ratios according to the high and low pressure ratios, the constant p, and the constant q. Determine the corrected target pressure ratio according to the target pressure ratio, the first function, and the second function. Determine the operating mode of the heat pump system according to the corrected target pressure ratio.

[0008] According to the control method for a two-stage compression heat pump system provided by the present invention, the step of determining the target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure includes: Determine the target pressure ratio of the heat pump system according to the ratio of the set discharge pressure to the set suction pressure.

[0009] According to the control method for a two-stage compression heat pump system provided by the present invention, the step of determining the operating mode of the heat pump system according to the corrected target pressure ratio includes: Determine the operating mode of the heat pump system according to the corrected target pressure ratio and the target pressure ratio ranges corresponding to the respective operating modes.

[0010] According to the control method for a two-stage compression heat pump system provided by the present invention, the step of determining the operating mode of the heat pump system according to the corrected target pressure ratio and the target pressure ratio ranges corresponding to the operating modes includes: When the corrected target pressure ratio is not greater than the first target pressure ratio, determine that the operating mode of the heat pump system is the single-stage non-increasing enthalpy mode; When the corrected target pressure ratio is greater than the first target pressure ratio and not greater than the second target pressure ratio, determine that the operating mode of the heat pump system is the single-stage increasing enthalpy mode; When the corrected target pressure ratio is greater than the second target pressure ratio and not greater than the third target pressure ratio, determine that the operating mode of the heat pump system is the two-stage non-increasing enthalpy mode; When the corrected target pressure ratio is greater than the third target pressure ratio, determine that the operating mode of the heat pump system is the two-stage increasing enthalpy mode.

[0011] According to the control method of the two-stage compression heat pump system provided by the present invention, after determining the operating mode of the heat pump system according to the target pressure ratio, ambient temperature and the high and low pressure ratios of the heat pump system, it further includes: According to the operating mode of the heat pump system, determine the operating frequencies of the high-stage compressor and the low-stage compressor, so that the heat pump system operates at the maximum energy efficiency or the maximum frequency.

[0012] According to the control method of the two-stage compression heat pump system provided by the present invention, determining the operating frequencies of the high-stage compressor and the low-stage compressor according to the operating mode of the heat pump system, so that the heat pump system operates at the maximum energy efficiency or the maximum frequency, includes: In the two-stage increasing enthalpy mode, determine that the operating frequencies of both the high-stage compressor and the low-stage compressor are rated frequencies, so that the heat pump system operates at the maximum frequency; When not in the two-stage increasing enthalpy mode, determine the operating frequencies of the high-stage compressor and the low-stage compressor according to the saturated temperature of the discharge pressure of the high-stage compressor and the saturated temperature of the suction pressure of the low-stage compressor, so that the heat pump system operates at the maximum energy efficiency.

[0013] According to the control method of the two-stage compression heat pump system provided by the present invention, determining the operating frequencies of the high-stage compressor and the low-stage compressor according to the saturated temperature of the discharge pressure of the high-stage compressor and the saturated temperature of the suction pressure of the low-stage compressor, so that the heat pump system operates at the maximum energy efficiency, includes: Determine a third function according to the saturated temperature of the discharge pressure, the saturated temperature of the suction pressure, constant k1, constant k2 and constant k3; Determine the optimal intermediate temperature according to the third function; Determine the operating frequencies of the high-pressure stage compressor and the low-pressure stage compressor according to the optimal intermediate temperature and the suction pressure saturation temperature of the high-pressure stage compressor, so that the heat pump system operates at the maximum energy efficiency.

[0014] The third aspect of the present invention provides a control device for a two-stage compression heat pump system, adopting the control method of the two-stage compression heat pump system described in any one of the above. The control device includes: An acquisition module that acquires the set discharge pressure of the high-pressure stage compressor and the set suction pressure of the low-pressure stage compressor; A first determination module for determining the target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure; A second determination module for determining the operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system.

[0015] The two-stage compression heat pump system provided by the present invention increases the flexibility of the heat pump system regulation by setting two-stage variable frequency compressors; a first one-way valve is connected in parallel beside the high-pressure stage compressor, and the system can be switched between single-stage operation and two-stage operation according to the actual working conditions, avoiding the situation of still two-stage compression under small temperature difference conditions, reducing the large exergy loss of the heat pump system, and improving the energy efficiency of the heat pump system; combined with the second one-way valve and the third throttle valve, the heat pump system can be switched between different operating modes, aiming to enable the heat pump system to achieve the optimal energy efficiency or the maximum capacity in the current mode. It solves the problems existing in the two-stage compression heat pump system in the prior art, such as low regulation flexibility, still two-stage compression under small temperature difference conditions, large exergy loss, and low energy efficiency.

[0016] The control method of the two-stage compression heat pump system provided by the present invention comprehensively considers different operating conditions of the two-stage compression heat pump system, including ambient conditions, actual operating pressure ratio conditions, and set outlet water temperature, etc., which can enable the heat pump system to accurately switch among four modes, avoiding the situation of still two-stage compression under small temperature difference conditions, reducing the large exergy loss of the heat pump system, and improving the energy efficiency of the heat pump system. It solves the problems existing in the two-stage compression heat pump system in the prior art, such as low regulation flexibility, still two-stage compression under small temperature difference conditions, large exergy loss, and low energy efficiency. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 It is one of the schematic flowcharts of the control method for the two-stage compression heat pump system provided by the present invention.

[0019] Figure 2 It is the second of the schematic flowcharts of the control method for the two-stage compression heat pump system provided by the present invention.

[0020] Figure 3 It is the schematic structural diagram of the control device for the two-stage compression heat pump system provided by the present invention.

[0021] Figure 4 It is the schematic structural diagram of the two-stage compression heat pump system provided by the present invention.

[0022] Figure 5 It is the schematic structural diagram of the electronic device provided by the present invention.

[0023] Reference numerals: 110, high-pressure stage compressor; 120, low-pressure stage compressor; 130, economizer; 140, condenser; 150, evaporator; 160, oil separator; 170, gas-liquid separator; 180, four-way valve; 190, oil return capillary; 101, first check valve; 102, second check valve; 201, first throttle valve; 202, second throttle valve; 203, third throttle valve; 810, processor; 820, communication interface; 830, memory; 840, communication bus. Detailed implementation manners

[0024] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0025] In the embodiments of the present invention, "at least one" means one or more, and "a plurality" means two or more. "And / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Here, A and B may be singular or plural. In the written description of the present invention, the character " / " generally represents an "or" relationship between the associated objects before and after. In addition, it should be noted that the serial numbers assigned to the objects described in the present invention itself, such as "first", "second", etc., are only used to distinguish the described objects and do not have any sequential or technical meanings.

[0026] In the commonly used two-stage compression heat pump system for providing high-temperature hot water, there are three combined forms of compressor operation: First, the high-pressure stage compressor uses a fixed-frequency compressor, and the low-pressure stage compressor uses a variable-frequency compressor. Capacity adjustment is achieved by starting and stopping the high-pressure stage compressor or by variable-frequency adjustment of the low-pressure stage compressor. The frequency adjustment of the low-pressure stage compressor simultaneously controls the intermediate pressure of the system, and the intermediate pressure is related to the system energy efficiency. The frequency operating range of the low-pressure stage compressor is determined by the ambient temperature range at that time to achieve better system energy efficiency. However, the disadvantage of this system is that the fixed frequency of the high-pressure stage compressor cannot be adjusted, and it can only be adjusted by starting and stopping, resulting in lagging and inflexible adjustment; the control of the low-pressure stage compressor is determined by either the ambient temperature or the geometric mean of the high and low pressures, ignoring dynamic characteristics such as the real-time water outlet temperature of the system and the real-time operating conditions of the system, resulting in untimely control and often unable to accurately reach the energy efficiency optimum point; two-stage compression is still carried out under the condition of a small temperature difference between the evaporation temperature and the condensation temperature, which will cause large exergy losses and low energy efficiency, resulting in a large amount of energy waste.

[0027] Second, both the high-pressure stage compressor and the low-pressure stage compressor use variable-frequency compressors, and the two are combined to adjust the system capacity. Although this system can control the high-pressure stage compressor and the low-pressure stage compressor more flexibly simultaneously, the control of the low-pressure stage compressor is still determined by either the ambient temperature or the geometric mean of the high and low pressures, ignoring dynamic characteristics such as the real-time water outlet temperature of the system and the real-time operating conditions of the system, resulting in untimely control and often unable to accurately reach the energy efficiency optimum point; two-stage compression is still carried out under the condition of a small temperature difference between the evaporation temperature and the condensation temperature, which will cause large exergy losses and low energy efficiency, resulting in a large amount of energy waste.

[0028] Third, one of the high-pressure stage compressor or the low-pressure stage compressor can be shut down, and the heat pump system can operate in a single stage under low-load or small temperature difference conditions. Although this system can switch to single-stage operation under small temperature difference conditions, the switching point setting is often unreasonable. The switching point is set according to the ambient temperature, and the judgment of the switching point is single and cannot reflect the dynamic performance, still resulting in a large amount of energy waste.

[0029] The following is combined with Figures 1 to 5The dual-stage compression heat pump system, control method and control device of the present invention. Among them, the execution subject of the control method of the dual-stage compression heat pump system is an electronic device or a server. The electronic device can be a personal computer (PC), a portable device, a laptop computer, a smart phone, a tablet computer, a portable wearable device and other devices; the server can refer to a single server, or a server cluster, a cloud server, etc. composed of multiple servers. The present invention does not specifically limit the specific form of the electronic device or the server. Further, the control method of the dual-stage compression heat pump system can also be applied to the control device of the dual-stage compression heat pump system provided in the electronic device or the server, and the control device of the dual-stage compression heat pump system can be implemented by software, hardware or a combination of both. The following takes the execution subject of the control method of the dual-stage compression heat pump system as the control device as an example to describe the control method of the dual-stage compression heat pump system.

[0030] To facilitate the understanding of the control method of the dual-stage compression heat pump system provided by the embodiments of the present invention, the control method of the dual-stage compression heat pump system provided by the present invention will be described in detail through the following several exemplary embodiments. It can be understood that these several exemplary embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments.

[0031] As Figure 4 shown, an embodiment of the third aspect of the present invention provides a dual-stage compression heat pump system. The dual-stage compression heat pump system includes a high-pressure stage compressor 110, a low-pressure stage compressor 120, a first check valve 101, a condenser, an economizer 130, an evaporator 150 and a third throttle valve 203.

[0032] Among them, both the high-pressure stage compressor 110 and the low-pressure stage compressor 120 are variable-frequency compressors; the air inlet of the high-pressure stage compressor 110 is communicated with the air outlet of the low-pressure stage compressor 120; the first check valve 101 is connected in parallel with the high-pressure stage compressor 110; the economizer 130 has a first heat exchange tube and a second heat exchange tube; one end of the first heat exchange tube is communicated with the air outlet of the high-pressure stage compressor 110 through the condenser 140, and the other end of the first heat exchange tube is communicated with the air inlet of the low-pressure stage compressor 120 through the evaporator 150; one end of the second heat exchange tube is communicated with the condenser 140 through the second throttle valve 202, and the other end is communicated with the air outlet of the low-pressure stage compressor 120 through the second check valve 102; one end of the third throttle valve 203 is communicated with the inlet of the second check valve 102, and the other end is communicated with the gas supplement port of the low-pressure stage compressor 120.

[0033] In this embodiment, by setting a two-stage variable-frequency compressor, the flexibility of the heat pump system regulation is increased. A first one-way valve 101 is connected in parallel beside the high-pressure stage compressor 110, and the system can be switched between single-stage operation and two-stage operation according to actual working conditions, such as load, ambient working conditions, and dynamic operating conditions of the system, avoiding the situation of still two-stage compression under small temperature difference conditions, reducing the exergy loss of the heat pump system, and improving the energy efficiency of the heat pump system. Together with the second one-way valve 102 and the third throttle valve 203, the heat pump system can be switched between different operating modes, aiming to enable the heat pump system to achieve the optimal energy efficiency or maximum capacity in the current mode, solving the problems of low regulation flexibility, still two-stage compression under small temperature difference conditions, large exergy loss, and low energy efficiency existing in the two-stage compression heat pump system in the prior art.

[0034] Furthermore, the two-stage compression heat pump system further includes a four-way valve 180; the D pipe of the four-way valve 180 is communicated with the outlet of the high-pressure stage compressor 110, the S pipe of the four-way valve 180 is communicated with the inlet of the low-pressure stage compressor 120, the E pipe of the four-way valve 180 is communicated with the evaporator 150, and the C pipe of the four-way valve 180 is communicated with the condenser 140. By switching the four-way valve 180, the heat pump system is switched between the refrigeration and heating modes.

[0035] The operating modes of the two-stage compression heat pump system in this embodiment include a two-stage non-increasing enthalpy mode, a two-stage increasing enthalpy mode, a single-stage non-increasing enthalpy mode, and a single-stage increasing enthalpy mode.

[0036] The process of the bipolar non-increasing enthalpy mode is as follows: The first throttle valve 201 and the second throttle valve 202 are opened, and the third throttle valve 203 is closed; both the high-pressure stage compressor 110 and the low-pressure stage compressor 120 are opened. The heat pump system cycle is that the refrigerant fluid enters the low-pressure stage compressor 120 for compression, mixes with the gas-liquid two-phase refrigerant flowing from the economizer 130, then enters the high-pressure stage compressor 110 for compression, exchanges heat at the condenser 140 to produce hot water, and then the refrigerant is divided into two paths. One path passes through the throttle of the second throttle valve 202 and enters the second heat exchange tube, exchanges heat with the non-throttled refrigerant in the first heat exchange tube at the economizer 130, flows to the inlet of the high-pressure stage compressor 110, and mixes with the exhaust gas of the low-pressure stage compressor 120; the other path exchanges heat at the economizer 130, passes through the throttle of the first throttle valve 201, flows to the evaporator 150 to exchange heat with the air, and then flows into the inlet of the low-pressure stage compressor 120. This mode is suitable for situations where the ambient temperature is relatively low or the temperature difference for producing hot water is relatively large.

[0037] The process of the two-stage increasing enthalpy mode is as follows: The first throttle valve 201, the second throttle valve 202, and the third throttle valve 203 are opened. Both the low-stage compressor 120 and the high-stage compressor 110 are turned on. In the heat pump system cycle, after the refrigerant fluid enters the low-stage compressor 120 and is compressed, it is mixed with the gas-liquid two-phase refrigerant flowing from the economizer 130, then enters the high-stage compressor 110 for compression, exchanges heat at the condenser 140 to produce hot water, and then the refrigerant is divided into two paths. One path passes through the throttle of the second throttle valve 202 and enters the second heat exchange tube, exchanges heat with the unthrottled refrigerant in the first heat exchange tube at the economizer 130, part of it flows to the intake port of the high-stage compressor 110 and is mixed with the exhaust gas of the low-stage compressor 120, and the other part flows through the third throttle valve 203 to the enthalpy-increasing gas supply port of the low-stage compressor 120; the other path exchanges heat at the economizer 130, is throttled by the first throttle valve 201, flows to the evaporator 150 to exchange heat with the air, and then flows into the intake port of the low-stage compressor 120. This mode is suitable for situations where the ambient temperature is extremely low or the temperature difference for producing hot water is very large. It enables the system to be in the maximum capacity output mode.

[0038] The process of the single-stage non-enthalpy-increasing mode is as follows: The first throttle valve 201 is opened, and the second throttle valve 202 and the third throttle valve 203 are closed. The low-stage compressor 120 is turned on, and the high-stage compressor 110 is turned off. In the heat pump system cycle, after the refrigerant fluid enters the low-stage compressor 120 and is compressed, it flows through the first one-way valve 101 beside the high-stage compressor 110, exchanges heat at the condenser 140 to produce hot water, then passes through the first throttle valve 201 for throttling, flows to the evaporator 150 to exchange heat with the air, and then flows into the intake port of the low-stage compressor 120. This mode is suitable for situations where the ambient temperature is relatively high, or the temperature difference for producing hot water is very small, or the actual pressure ratio is relatively small.

[0039] The process of the single-stage enthalpy-increasing mode is as follows: The first throttle valve 201, the second throttle valve 202, and the third throttle valve 203 are opened. The low-stage compressor 120 is turned on, and the high-stage compressor 110 is turned off. In the heat pump system cycle, after the refrigerant fluid enters the low-stage compressor 120 and is compressed, it flows through the first one-way valve 101 beside the high-stage compressor 110, exchanges heat at the condenser 140 to produce hot water, and then the refrigerant is divided into two paths. One path passes through the throttle of the second throttle valve 202 and exchanges heat with the unthrottled refrigerant at the economizer 130, part of it flows to the intake port of the high-stage compressor 110 and is mixed with the exhaust gas of the low-stage compressor 120, and the other part flows through the third throttle valve 203 to the enthalpy-increasing gas supply port of the low-stage compressor 120; the other path exchanges heat at the economizer 130, is throttled by the first throttle valve 201, flows to the evaporator 150 to exchange heat with the air, and then flows into the intake port of the low-stage compressor 120. This mode is suitable for situations where the ambient temperature is not extremely low, or the temperature difference for producing hot water is not large.

[0040] Specifically, when the heat pump system switches to the two-stage non-increasing enthalpy mode, the control device controls the first throttle valve 201 and the second throttle valve 202 to open, controls the third throttle valve 203 to close, and controls both the low-pressure stage compressor 120 and the high-pressure stage compressor 110 to open.

[0041] Specifically, when the heat pump system switches to the two-stage increasing enthalpy mode, the control device controls the first throttle valve 201, the second throttle valve 202, and the third throttle valve 203 to all open. It controls both the low-pressure stage compressor 120 and the high-pressure stage compressor 110 to open.

[0042] Specifically, when the heat pump system switches to the single-stage non-increasing enthalpy mode, the control device controls the first throttle valve 201 to open, controls the second throttle valve 202 and the third throttle valve 203 to both close. It controls the low-pressure stage compressor 120 to open and controls the high-pressure stage compressor 110 to close.

[0043] Specifically, when the heat pump system switches to the single-stage increasing enthalpy mode, the control device controls the first throttle valve 201, the second throttle valve 202, and the third throttle valve 203 to all open. It controls the low-pressure stage compressor 120 to open and controls the high-pressure stage compressor 110 to close.

[0044] It can be understood that the economizer 130 can be replaced by a flash tank.

[0045] Furthermore, the two-stage compression heat pump system further includes an oil-gas separator 160. The oil-gas separator 160 is installed between the outlet of the high-pressure stage compressor 110 and the D pipe of the four-way valve 180. The oil-gas separator 160 is also connected to the inlet of the low-pressure stage compressor 120 through an oil return capillary 190. By setting the oil-gas separator 160, heating and oil-gas separation of the hydraulic oil in the high-pressure stage compressor 110 and the low-pressure stage compressor 120 can be achieved, improving the service life of the compressor.

[0046] Furthermore, the two-stage compression heat pump system further includes a gas-liquid separator 170; one end of the gas-liquid separator 170 is connected to the inlet of the low-pressure stage compressor 120, and the other end is connected to the S pipe of the four-way valve 180. By setting the gas-liquid separator 170, liquid slugging can be prevented, protecting the compressor.

[0047] As Figure 1 shown, a specific embodiment of the first aspect of the present invention provides a control method for a two-stage compression heat pump system. Among them, the operating modes of the two-stage compression heat pump system include a two-stage non-increasing enthalpy mode, a two-stage increasing enthalpy mode, a single-stage non-increasing enthalpy mode, and a single-stage increasing enthalpy mode. This control method includes S100, S200, and S300.

[0048] S100. Obtain the set discharge pressure of the high-pressure stage compressor 110 and the set suction pressure of the low-pressure stage compressor 120.

[0049] Specifically, the control device of the two-stage compression heat pump system obtains the set discharge pressure of the high-stage compressor 110 and the set suction pressure of the low-stage compressor 120.

[0050] S200. Determine the target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure.

[0051] Furthermore, determine the target pressure ratio of the heat pump system according to the ratio of the set discharge pressure to the set suction pressure. Specifically, the target pressure ratio PR d is the ratio of the set discharge pressure Pdh to the set suction pressure Psl, as shown in formula (1).

[0052] Formula (1).

[0053] Specifically, the control device, based on the obtained set discharge pressure Pdh and set suction pressure Psl, takes the ratio of the set discharge pressure Pdh to the set suction pressure Psl as the target pressure ratio PR of the heat pump system. d .

[0054] S300. Determine the operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system.

[0055] Specifically, the control device determines the operating mode of the heat pump system according to the calculated target pressure ratio PR d , the current ambient temperature T, and the current high and low pressure ratios PR of the heat pump system.

[0056] In this embodiment, different operating conditions of the two-stage compression heat pump system are comprehensively considered, including ambient conditions, actual operating pressure ratio conditions, and set outlet water temperature, etc. It can enable the heat pump system to accurately switch among four modes, avoid the situation of still having two-stage compression under small temperature difference conditions, reduce the large exergy loss of the heat pump system, improve the energy efficiency of the heat pump system, and solve the problems existing in the two-stage compression heat pump system in the prior art, such as low flexibility of regulation, still having two-stage compression under small temperature difference conditions, large exergy loss, and low energy efficiency.

[0057] It should be noted that the high and low pressure ratios of the heat pump system reflect the operating efficiency and performance of the heat pump system. The normal pressure ratio range can help technicians determine whether the heat pump is operating efficiently or whether there are potential problems. For example, if the pressure ratio is too high or too low, it may indicate that there is a fault inside the system or maintenance is required.

[0058] It should be noted that the set exhaust pressure can be determined according to the set water outlet temperature and the relationship between the set water outlet temperature and the set exhaust pressure. Therefore, this embodiment also takes into account the influence of the set water outlet temperature on the system operation mode, making the selection of the operation mode more accurate.

[0059] In some embodiments, the operation mode of the heat pump system is determined according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system, including: Determine the first function of the ambient temperature according to the ambient temperature, the constant m, and the constant n; Determine the second function of the high and low pressure ratios according to the high and low pressure ratios, the constant p, and the constant q; Determine the corrected target pressure ratio according to the target pressure ratio, the first function, and the second function; Determine the operation mode of the heat pump system according to the corrected target pressure ratio.

[0060] In this embodiment, the definition of the corrected target pressure ratio takes into account the comprehensive influence of the system high-pressure stage exhaust pressure, the low-pressure stage suction pressure, the current ambient temperature, and the current actual operating high and low pressure ratios. In this way, by determining the operation mode of the heat pump system through the corrected target pressure ratio, a more accurate switching of the operation mode can be achieved, avoiding the situation of still using two-stage compression under small temperature difference conditions, reducing the exergy loss of the heat pump system, and improving the energy efficiency of the heat pump system.

[0061] Specifically, first, the control device determines the first function of the ambient temperature according to the ambient temperature, the constant m, and the constant n; and determines the second function of the high and low pressure ratios according to the high and low pressure ratios, the constant p, and the constant q. Then, the control device determines the corrected target pressure ratio according to the sum of the target pressure ratio, the first function, and the second function. Finally, the control device determines the operation mode of the heat pump system according to the corrected target pressure ratio.

[0062] Exemplarily, determining the first function of the ambient temperature according to the ambient temperature, the constant m, and the constant n includes: The control device determines the first function of the ambient temperature according to formula (2).

[0063] F1 = m×T + n Formula (2).

[0064] In formula (2), F1 is the first function and T is the ambient temperature.

[0065] It should be noted that by conducting experiments on different models, the constants m and n can be determined. The determination method of the constants m and n is not limited here and can be selected according to the actual situation. Exemplarily, the corresponding relationship between the model and the constants m and n can be preset in the control device, and when the constants m and n are needed, the constants m and n can be directly retrieved based on the model of the compressor of the heat pump system.

[0066] It is understandable that the ambient temperature can be detected by a temperature detection unit such as a thermometer.

[0067] Exemplarily, according to the high-low pressure ratio, constant p, and constant q, determining a second function of the high-low pressure ratio includes: The control device determines the second function of the high-low pressure ratio according to formula (3).

[0068] F2 = p × PR + q Formula (3).

[0069] In formula (3), F2 is the second function, and PR is the high-low pressure ratio.

[0070] It should be noted that by conducting experiments on different models, constants p and q can be determined. The determination methods of constants p and q are not limited here and can be selected according to the actual situation. Exemplarily, the corresponding relationship between the model and constants p and q can be preset in the control device. When constants p and q are needed, constants p and q can be directly retrieved based on the model of the compressor of the heat pump system.

[0071] It is understandable that the high-low pressure ratio PR of the heat pump system refers to the pressure ratio between the high-pressure side and the low-pressure side in the heat pump system. In the heat pump system, the high-pressure side usually refers to the pressure of the condenser, while the low-pressure side refers to the pressure of the evaporator. The ratio of high pressure to low pressure has an important impact on the performance and efficiency of the system.

[0072] It is understandable that the pressure of the condenser and the pressure of the evaporator can be detected by a pressure detection unit such as a pressure sensor, so as to determine the high-low pressure ratio PR of the heat pump system.

[0073] Furthermore, according to the target pressure ratio, the first function, and the second function, determining the corrected target pressure ratio includes: Determining the corrected target pressure ratio according to the sum of the target pressure ratio, the first function, and the second function.

[0074] Specifically, the control device determines the corrected target pressure ratio according to formula (4).

[0075] PR* = PR d + F1 + F2 Formula (4).

[0076] In formula (4), PR* is the corrected target pressure ratio, and PR d is the target pressure ratio.

[0077] Furthermore, according to the corrected target pressure ratio, determining the operating mode of the heat pump system includes: Determine the operating mode of the heat pump system according to the corrected target pressure ratio and the target pressure ratio ranges corresponding to the respective operating modes. This can ensure that the heat pump system accurately and quickly switches its operating mode.

[0078] Specifically, determining the operating mode of the heat pump system according to the corrected target pressure ratio and the target pressure ratio ranges corresponding to the operating modes includes: When the corrected target pressure ratio is not greater than the first target pressure ratio value, determine that the operating mode of the heat pump system is the single-stage non-increasing enthalpy mode; When the corrected target pressure ratio is greater than the first target pressure ratio value and not greater than the second target pressure ratio value, determine that the operating mode of the heat pump system is the single-stage increasing enthalpy mode; When the corrected target pressure ratio is greater than the second target pressure ratio value and not greater than the third target pressure ratio value, determine that the operating mode of the heat pump system is the two-stage non-increasing enthalpy mode; When the corrected target pressure ratio is greater than the third target pressure ratio value, determine that the operating mode of the heat pump system is the two-stage increasing enthalpy mode.

[0079] In this embodiment, comparing the corrected target pressure ratio with the target pressure ratio ranges corresponding to the preset operating modes can further improve the accuracy and timeliness of the operating mode switching.

[0080] As Figure 2 shown, in some embodiments, after determining the operating mode of the heat pump system according to the target pressure ratio, ambient temperature, and high and low pressure ratios of the heat pump system, it further includes: S400. Determine the operating frequencies of the high-pressure stage compressor 110 and the low-pressure stage compressor 120 according to the operating mode of the heat pump system, so that the heat pump system operates at the maximum energy efficiency or the maximum frequency.

[0081] In this embodiment, after determining the operating mode of the heat pump system, adjust the operating frequencies of the high-pressure stage compressor 110 and the low-pressure stage compressor 120 to ensure that the heat pump system can operate at the maximum energy efficiency or the maximum frequency.

[0082] Further, determining the operating frequencies of the high-pressure stage compressor 110 and the low-pressure stage compressor 120 according to the operating mode of the heat pump system, so that the heat pump system operates at the maximum energy efficiency or the maximum frequency, includes: In the two-stage increasing enthalpy mode, determine that the operating frequencies of both the high-pressure stage compressor 110 and the low-pressure stage compressor 120 are the rated frequencies, so that the heat pump system operates at the maximum frequency; When not in the two-stage increasing enthalpy mode, determine the operating frequencies of the high-pressure stage compressor 110 and the low-pressure stage compressor 120 according to the saturated temperature of the discharge pressure of the high-pressure stage compressor 110 and the saturated temperature of the suction pressure of the low-pressure stage compressor 120, so that the heat pump system operates at the maximum energy efficiency.

[0083] In this embodiment, the heat pump system can flexibly adjust the system capacity under different environmental conditions, automatically switch to the operation mode with the optimal energy efficiency or the maximum capacity, and make full and effective use of the outdoor air heat energy. This control method adaptively adjusts the system operation according to different environmental conditions, enabling the system to efficiently supply heat whether in low-temperature or high-temperature environmental conditions.

[0084] In the two-stage enthalpy-increasing mode, control the high-stage compressor 110 and the low-stage compressor 120 to operate at the rated frequency, indicating that the heat pump system is operating at the maximum energy efficiency at this time, avoiding adjusting the compressor, simplifying the control logic, and improving the control speed. When not in the two-stage enthalpy-increasing mode, adjust the frequencies of the high-stage compressor 110 and the low-stage compressor 120 to make the heat pump system operate at the maximum energy efficiency, which can prevent overshoot, improve the adjustment speed, ensure that the heat pump system can still operate at the maximum energy efficiency, and ensure that the heat pump system can still achieve the optimal energy efficiency or the maximum capacity in the operation mode.

[0085] Specifically, when the heat pump system is in the two-stage enthalpy-increasing mode, the control device determines that the operating frequencies of the high-stage compressor 110 and the low-stage compressor 120 are both the rated frequencies, and controls the high-stage compressor 110 and the low-stage compressor 120 of the heat pump system to work at the rated frequencies to ensure that the heat pump system operates at the maximum frequency.

[0086] When the heat pump system is not in the two-stage enthalpy-increasing mode, the control device determines the operating frequencies of the high-stage compressor 110 and the low-stage compressor 120 according to the exhaust pressure saturation temperature of the high-stage compressor 110 and the suction pressure saturation temperature of the low-stage compressor 120 to ensure that the heat pump system can operate at the maximum energy efficiency.

[0087] Furthermore, determining the operating frequencies of the high-stage compressor 110 and the low-stage compressor 120 according to the exhaust pressure saturation temperature of the high-stage compressor 110 and the suction pressure saturation temperature of the low-stage compressor 120 to make the heat pump system operate at the maximum energy efficiency includes: Determine the third function according to the exhaust pressure saturation temperature, the suction pressure saturation temperature, the constant k1, the constant k2, and the constant k3; Determine the optimal intermediate temperature according to the third function; Determine the operating frequencies of the high-stage compressor 110 and the low-stage compressor 120 according to the optimal intermediate temperature and the suction pressure saturation temperature of the high-stage compressor 110 to make the heat pump system operate at the maximum energy efficiency.

[0088] In this embodiment, by precisely controlling the operating frequency and intermediate temperature of the compressor, the heat pump system can operate in an optimal state, thereby improving the energy efficiency ratio and refrigeration efficiency of the system. Improving energy efficiency means reducing energy consumption and greenhouse gas emissions, which is beneficial to environmental protection and sustainable development. By optimizing the operating frequency and intermediate temperature of the compressor, the fluctuations and unstable factors of the system can be reduced, and the stability and reliability of the system can be improved. Improving energy efficiency and stable operation can reduce the operating cost and maintenance cost of the system, bringing better economic benefits to users.

[0089] Specifically, according to the discharge pressure saturation temperature, suction pressure saturation temperature, constant k1, constant k2, and constant k3, determining the third function includes: Determine the third function according to formula (5).

[0090] F3 = k1 × Pdh_t + k2 × Psl_t + k3 Formula (5).

[0091] In formula (5), F3 is the third function; Pdh_t is the discharge pressure saturation temperature of the high-pressure stage compressor; Psl_t is the suction pressure saturation temperature of the low-pressure stage compressor.

[0092] It should be noted that by conducting experiments on different models, the specific values of constants k1, k2, and k3 can be determined. The determination methods of constants k1, k2, and k3 are not limited here and can be selected according to actual situations. Exemplarily, the corresponding relationship between the model and constants k1, k2, and k3 can be preset in the control device. When constants k1, k2, and k3 are needed, constants k1, k2, and k3 can be directly retrieved based on the model of the compressor of the heat pump system.

[0093] Exemplarily, according to the optimal intermediate temperature and the suction pressure saturation temperature of the high-pressure stage compressor 110, determining the operating frequencies of the high-pressure stage compressor 110 and the low-pressure stage compressor 120 includes: When the suction pressure saturation temperature of the high-pressure stage compressor 110 is higher than the optimal intermediate temperature, control the operating frequencies of the high-pressure stage compressor 110 and the low-pressure stage compressor 120 to decrease; When the suction pressure saturation temperature of the high-pressure stage compressor 110 is lower than the optimal intermediate temperature, control the operating frequencies of the high-pressure stage compressor 110 and the low-pressure stage compressor 120 to increase.

[0094] In this embodiment, the control device compares the suction pressure saturation temperature of the high-pressure stage compressor 110 with the optimal intermediate temperature, and outputs corresponding control instructions according to the comparison result to control the high-pressure stage compressor 110 and the low-pressure stage compressor 120 to adjust in a timely manner, ensuring that the heat pump system always operates at the maximum energy efficiency.

[0095] As shown Figure 3 in the figure, a control device for a two-stage compression heat pump system is provided in a specific embodiment of the second aspect of the present invention. The control method of the two-stage compression heat pump system according to any of the above embodiments is adopted. The control device of the two-stage compression heat pump system includes an acquisition module, a first determination module, and a second determination module; the acquisition module acquires the set discharge pressure of the high-pressure stage compressor 110 and the set suction pressure of the low-pressure stage compressor 120; the first determination module is used to determine the target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure; the second determination module is used to determine the operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system.

[0096] The control device of this embodiment comprehensively considers the environmental conditions, actual operating conditions, and set outlet water temperature of the heat pump system, can accurately switch the operating mode of the heat pump system, avoid the situation of still performing two-stage compression under small temperature difference conditions, reduce the large exergy loss of the heat pump system, improve the energy efficiency of the heat pump system, and solve the problems of low flexibility in regulation, still performing two-stage compression under small temperature difference conditions, large exergy loss, and low energy efficiency existing in the two-stage compression heat pump system in the prior art.

[0097] Figure 5 A schematic diagram of the physical structure of an electronic device is exemplified. As shown Figure 5 in the figure, the electronic device may include: a processor 810, a communication interface 820, a memory 830, and a communication bus 840. Among them, the processor 810, the communication interface 820, and the memory 830 complete mutual communication through the communication bus 840. The processor 810 can call the logical instructions in the memory 830 to execute the control method of the two-stage compression heat pump system. The method includes: acquiring the set discharge pressure of the high-pressure stage compressor and the set suction pressure of the low-pressure stage compressor. Determining the target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure. Determining the operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system.

[0098] In addition, when the logical instructions in the above-mentioned memory 830 are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0099] On the other hand, the present invention also provides a computer program product. The computer program product includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the control method of the two-stage compression heat pump system provided by the above-mentioned various methods. The method includes: obtaining the set discharge pressure of the high-pressure stage compressor and the set suction pressure of the low-pressure stage compressor. According to the set discharge pressure and the set suction pressure, determining the target pressure ratio of the heat pump system. According to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system, determining the operating mode of the heat pump system.

[0100] On another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it is implemented to execute the control method of the two-stage compression heat pump system provided by the above-mentioned various methods. The method includes: obtaining the set discharge pressure of the high-pressure stage compressor and the set suction pressure of the low-pressure stage compressor. According to the set discharge pressure and the set suction pressure, determining the target pressure ratio of the heat pump system. According to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system, determining the operating mode of the heat pump system.

[0101] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative labor.

[0102] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A two-stage compression heat pump system, characterized in that, Comprising: A high-pressure stage compressor (110) and a low-pressure stage compressor (120), both being variable-frequency compressors; An air inlet of the high-pressure stage compressor (110) is communicated with an air outlet of the low-pressure stage compressor (120); A first check valve (101), which is connected in parallel with the high-pressure stage compressor (110); An economizer (130), wherein the economizer (130) has a first heat exchange tube and a second heat exchange tube; one end of the first heat exchange tube is communicated with the air outlet of the high-pressure stage compressor (110) through a condenser (140), and the other end of the first heat exchange tube is communicated with the air inlet of the low-pressure stage compressor (120) through an evaporator (150); one end of the second heat exchange tube is communicated with the condenser (140) through a second throttle valve (202), and the other end is communicated with the air outlet of the low-pressure stage compressor (120) through a second check valve (102); A third throttle valve (203), one end of which is communicated with an inlet of the second check valve (102), and the other end is communicated with a gas supplement port of the low-pressure stage compressor (120).

2. The two-stage compression heat pump system according to claim 1, wherein Further comprising: A four-way valve (180), wherein a D pipe of the four-way valve (180) is communicated with the air outlet of the high-pressure stage compressor (110), an S pipe of the four-way valve (180) is communicated with the air inlet of the low-pressure stage compressor (120), an E pipe of the four-way valve (180) is communicated with the evaporator (150), and a C pipe of the four-way valve (180) is communicated with the condenser (140).

3. A control method for a two-stage compression heat pump system, characterized in that, For the two-stage compression heat pump system according to claim 1 or 2; The operation modes of the two-stage compression heat pump system include a two-stage non-enthalpy-increasing mode, a two-stage enthalpy-increasing mode, a single-stage non-enthalpy-increasing mode, and a single-stage enthalpy-increasing mode; the control method includes: Obtaining a set discharge pressure of the high-pressure stage compressor (110) and a set suction pressure of the low-pressure stage compressor (120); Determining a target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure; Determining the operation mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system.

4. The control method of the two-stage compression heat pump system according to claim 3, characterized in that, The determining the operation mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system includes: Determining a first function of the ambient temperature according to the ambient temperature, a constant m, and a constant n; Determining a second function of the high and low pressure ratios according to the high and low pressure ratios, a constant p, and a constant q; Determining a corrected target pressure ratio according to the target pressure ratio, the first function, and the second function; Determining the operation mode of the heat pump system according to the corrected target pressure ratio.

5. The control method of the two-stage compression heat pump system according to claim 3, wherein The determining the target pressure ratio of the heat pump system according to the set discharge pressure and the set suction pressure includes: Determining the target pressure ratio of the heat pump system according to a ratio of the set discharge pressure to the set suction pressure.

6. The control method of the two-stage compression heat pump system according to claim 4, characterized in that, The determining the operation mode of the heat pump system according to the corrected target pressure ratio includes: Determining the operation mode of the heat pump system according to the corrected target pressure ratio and the target pressure ratio ranges corresponding to the respective operation modes.

7. The control method of the two-stage compression heat pump system according to claim 6, characterized in that, Determining the operating mode of the heat pump system according to the corrected target pressure ratio and the target pressure ratio ranges corresponding to the respective operating modes includes: When the corrected target pressure ratio is not greater than the first target pressure ratio value, determining that the operating mode of the heat pump system is the single-stage non-increasing enthalpy mode; When the corrected target pressure ratio is greater than the first target pressure ratio value and not greater than the second target pressure ratio value, determining that the operating mode of the heat pump system is the single-stage increasing enthalpy mode; When the corrected target pressure ratio is greater than the second target pressure ratio value and not greater than the third target pressure ratio value, determining that the operating mode of the heat pump system is the two-stage non-increasing enthalpy mode; When the corrected target pressure ratio is greater than the third target pressure ratio value, determining that the operating mode of the heat pump system is the two-stage increasing enthalpy mode.

8. The control method of the two-stage compression heat pump system according to any one of claims 3 to 7, characterized in that, After determining the operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system, it further includes: According to the operating mode of the heat pump system, determining the operating frequencies of the high-pressure stage compressor (110) and the low-pressure stage compressor (120) so that the heat pump system operates at the maximum energy efficiency or the maximum frequency.

9. The control method of the two-stage compression heat pump system according to claim 8, characterized in that, The determining the operating frequencies of the high-pressure stage compressor (110) and the low-pressure stage compressor (120) according to the operating mode of the heat pump system so that the heat pump system operates at the maximum energy efficiency or the maximum frequency includes: In the two-stage increasing enthalpy mode, determining that the operating frequencies of both the high-pressure stage compressor (110) and the low-pressure stage compressor (120) are the rated frequencies so that the heat pump system operates at the maximum frequency; When not in the two-stage increasing enthalpy mode, determining the operating frequencies of the high-pressure stage compressor (110) and the low-pressure stage compressor (120) according to the saturation temperature of the discharge pressure of the high-pressure stage compressor (110) and the saturation temperature of the suction pressure of the low-pressure stage compressor (120) so that the heat pump system operates at the maximum energy efficiency.

10. The control method of the two-stage compression heat pump system according to claim 9, characterized in that, The determining the operating frequencies of the high-pressure stage compressor (110) and the low-pressure stage compressor (120) according to the saturation temperature of the discharge pressure of the high-pressure stage compressor (110) and the saturation temperature of the suction pressure of the low-pressure stage compressor (120) so that the heat pump system operates at the maximum energy efficiency includes: Determining a third function according to the saturation temperature of the discharge pressure, the saturation temperature of the suction pressure, constant k1, constant k2, and constant k3; Determining an optimal intermediate temperature according to the third function; Determining the operating frequencies of the high-pressure stage compressor (110) and the low-pressure stage compressor (120) according to the optimal intermediate temperature and the saturation temperature of the suction pressure of the high-pressure stage compressor (110) so that the heat pump system operates at the maximum energy efficiency.

11. A control device for a two-stage compression heat pump system, characterized in that, Using the control method of the two-stage compression heat pump system according to any one of claims 3 to 10, the control device includes: An acquisition module that acquires the set discharge pressure of the high-pressure stage compressor (110) and the set suction pressure of the low-pressure stage compressor (120); A first determination module, configured to determine a target pressure ratio of the heat pump system according to the set exhaust pressure and the set suction pressure; A second determination module, configured to determine an operating mode of the heat pump system according to the target pressure ratio, the ambient temperature, and the high and low pressure ratios of the heat pump system.

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