Control method suitable for exhaust temperature of low-temperature heat pump system

Abstract

The invention provides a control method suitable for the exhaust temperature of a low-temperature heat pump system, relates to the technical field of heat pump unit control, and aims to improve the heating efficiency of a heat pump at a low environment temperature and prevent the exhaust temperature from being too high during high-pressure-ratio operation so as to ensure the reliability of the system. The method is divided into three exhaust temperature control stages, namely a low exhaust temperature stage, a medium exhaust temperature stage and a high exhaust temperature stage. And in the low-temperature stage, the exhaust temperature is controlled by fixing the opening degree of the air supply expansion valve. And in the medium temperature stage, a plurality of control intervals are divided according to the evaporation temperature, the target exhaust superheat degree of each interval is calculated, and the opening degree of the air supply expansion valve is adjusted accordingly. And in the high-temperature stage, the air supply expansion valve is fully opened, and the direction and the opening degree of the liquid spraying electric control valve are adjusted according to the exhaust temperature change trend. By collecting the water outlet temperature of the shell-and-tube heat exchanger, the exhaust temperature of the compressor and the suction pressure, the system accurately adjusts the action of each control valve, and the performance of the system at the low temperature is improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat pump unit control, and in particular to a method for controlling exhaust temperature of a low-temperature heat pump system. Background Art

[0002] With the development of air source heat pump technology, further expanding the application scope of air source heat pumps and improving energy conversion efficiency are the future development trends and challenges. In recent years, the use of air source heat pumps has gradually spread to the cold northern regions. In areas with low ambient temperatures, the heat absorbed by the air source heat pump from the environment will decrease as the temperature drops, resulting in a decrease in evaporation temperature and pressure. In order to ensure the necessary outlet water temperature, the compressor needs to operate at a high compression ratio, which leads to problems such as excessively high exhaust temperature and reduced heating capacity.

[0003] To solve the above problems, low-temperature air source heat pumps generally use an air-injection reheat system. This system effectively reduces the exhaust temperature and improves the heating capacity and overall operating efficiency of the unit. The air-injection reheat system includes: an air-injection reheat compressor, an air-injection expansion valve, and an economizer. The air supply volume of the system is achieved by controlling the opening of the air-injection expansion valve.

[0004] At present, most heat pump manufacturers' air expansion valves are mainly controlled by fixed superheat or exhaust temperature at the inlet and outlet of the economizer. This method limits the flexibility of the air supply control range, makes it difficult to ensure the rationality of the air supply volume, and thus cannot guarantee the efficiency of the system in the entire operating range.

[0005] In addition, the control method of the liquid injection valve is mostly a simple on-off control, that is, when the exhaust temperature exceeds the set value, the liquid injection is turned on, and when it is lower than the set value, it is stopped. This control method is prone to cause drastic fluctuations in the exhaust temperature, which in turn affects the stable operation of the system and reduces energy efficiency. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method for controlling the exhaust temperature of a low-temperature heat pump system, thereby improving the heating capacity of an air source heat pump unit under low ambient temperature operation.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A method for controlling the exhaust temperature of a low-temperature heat pump system, the low-temperature heat pump system comprising: an air-injection reheat-increasing compressor, an electronic expansion valve, a shell and tube heat exchanger, a fin heat exchanger, an economizer, a gas-liquid separator, a four-way valve, an air-injection expansion valve and a liquid injection electric regulating valve, wherein one end of the air-injection reheat-increasing compressor is connected to a port on one side of the four-way valve; three ports on the other side of the four-way valve are respectively connected to one end of the shell and tube heat exchanger, one end of the fin heat exchanger and one end of the gas-liquid separator; the other end of the fin heat exchanger is connected through the The electronic expansion valve is respectively connected to one end of one side of the economizer, one end of the air-increasing expansion valve and one end of the liquid-injecting electric regulating valve; the other end of the shell-and-tube heat exchanger is connected to the other end of one side of the economizer; the other end of the air-increasing re-enthalpy compressor is connected to the other end of the gas-liquid separator; one end of the other side of the economizer is respectively connected to another end of the air-increasing re-enthalpy compressor and the other end of the liquid-injecting electric regulating valve; the other end of the other side of the economizer is connected to the other end of the air-increasing expansion valve; the control method comprises:

[0009] When the air-injection reheat-increasing compressor is in a working state under a heating model, the exhaust temperature at the outlet of the air-injection reheat-increasing compressor, the outlet water temperature of the shell and tube heat exchanger, and the suction pressure at the inlet of the air-injection reheat-increasing compressor are obtained;

[0010] determining an actual exhaust superheat according to the outlet water temperature and the exhaust temperature, and determining an evaporation temperature according to the suction pressure;

[0011] Determine a plurality of temperature control stages according to the exhaust temperature; the temperature control stages include a low exhaust temperature control stage, a medium exhaust temperature control stage and a high exhaust temperature control stage;

[0012] In the low exhaust temperature control stage, the openings of the liquid injection electric regulating valve and the air supplement expansion valve are controlled according to the exhaust temperature;

[0013] In the middle exhaust temperature control stage, a plurality of control intervals are determined according to the evaporation temperature, and a target exhaust superheat in each control interval is calculated, so as to control the opening of the air supplement expansion valve according to the target exhaust superheat and the actual exhaust superheat;

[0014] In the high exhaust temperature control stage, the opening of the liquid injection electric regulating valve is controlled according to the change trend of the exhaust temperature.

[0015] Preferably, determining the actual exhaust gas superheat according to the outlet water temperature and the exhaust gas temperature includes:

[0016] Add the water outlet temperature to the preset temperature to calculate the condensation temperature;

[0017] The actual exhaust gas superheat is obtained by subtracting the estimated condensation temperature from the exhaust gas temperature.

[0018] Preferably, determining the evaporation temperature according to the suction pressure comprises:

[0019] The saturation temperature corresponding to the suction pressure is determined as the evaporation temperature.

[0020] Preferably, a plurality of temperature control stages are determined according to the exhaust gas temperature, including:

[0021] When the exhaust temperature meets T 排气 <T1, the current temperature control stage is determined as the low exhaust temperature control stage;

[0022] When the exhaust temperature meets T1≤T 排气 <T2, the current temperature control stage is determined as the middle exhaust temperature control stage;

[0023] When the exhaust temperature meets T 排气 ≥T2, the current temperature control stage is determined as the high exhaust temperature control stage; wherein, T 排气 is the exhaust temperature; T1 is the threshold temperature of the first temperature control stage, and T2 is the threshold temperature of the second temperature control stage.

[0024] Preferably, in the low exhaust temperature control stage, controlling the opening of the liquid injection electric regulating valve and the air supplement expansion valve according to the exhaust temperature includes:

[0025] The working state of the liquid injection electric regulating valve is adjusted to a closed state, and at the same time, an initial opening is set for the air replenishment expansion valve, and the initial opening is set as a fixed opening.

[0026] Preferably, the calculation process of the target exhaust superheat comprises:

[0027] The exhaust superheat value corresponding to the optimal refrigeration coefficient at different condensing temperatures in each control range is measured through a preset experiment;

[0028] According to the corresponding exhaust superheat value, the relationship between the exhaust superheat and the condensation temperature is fitted;

[0029] The target exhaust gas superheat is determined according to a relationship between the exhaust gas superheat and the condensation temperature.

[0030] Preferably, controlling the opening of the air supplement expansion valve according to the target exhaust gas superheat and the actual exhaust gas superheat comprises:

[0031] When the actual exhaust gas superheat is greater than the target exhaust gas superheat, the opening of the air supplement expansion valve is controlled to increase through a PID control method;

[0032] When the actual exhaust gas superheat is less than the target exhaust gas superheat, the opening of the air supplement expansion valve is controlled to decrease through PID control.

[0033] Preferably, in the high exhaust temperature control stage, controlling the opening of the liquid injection electric regulating valve according to the change trend of the exhaust temperature includes:

[0034] When the temperature difference between the exhaust temperatures read in two adjacent detection cycles is greater than a preset first temperature difference trend threshold temperature, it is determined that the liquid injection electric regulating valve enters a fast regulation stage, and the regulation amplitude of each regulation cycle is A%;

[0035] When the temperature difference between the exhaust temperatures read in two detection cycles is less than the preset second temperature difference trend threshold temperature, it is determined that the liquid injection electric control valve needs to enter the slow adjustment stage, and the adjustment amplitude of each adjustment cycle is B%; wherein A is the first preset adjustment amplitude, and B is the second preset adjustment amplitude; A>B.

[0036] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0037] The present invention provides a method for controlling the exhaust temperature of a low-temperature heat pump system, wherein the low-temperature heat pump system comprises: an air-injection reheat-increasing compressor, an electronic expansion valve, a shell and tube heat exchanger, a fin heat exchanger, an economizer, a gas-liquid separator, a four-way valve, an air-injection expansion valve and a liquid injection electric regulating valve, wherein one end of the air-injection reheat-increasing compressor is connected to a port on one side of the four-way valve; three ports on the other side of the four-way valve are respectively connected to one end of the shell and tube heat exchanger, one end of the fin heat exchanger and one end of the gas-liquid separator; the fin exchange The other end of the heat exchanger is connected to one end of one side of the economizer, one end of the air-increasing expansion valve and one end of the liquid injection electric regulating valve through the electronic expansion valve; the other end of the shell and tube heat exchanger is connected to the other end of one side of the economizer; the other end of the air-increasing re-enthalpy compressor is connected to the other end of the gas-liquid separator; one end of the other side of the economizer is respectively connected to another end of the air-increasing re-enthalpy compressor and the other end of the liquid injection electric regulating valve; the other end of the other side of the economizer is connected to the other end of the air-increasing expansion valve one end is connected; the control method comprises: when the air-injection reheat-increasing compressor is in the working state under the heating model, obtaining the exhaust temperature of one end of the air-injection reheat-increasing compressor, the outlet water temperature of the shell and tube heat exchanger, and the suction pressure of the other end of the air-injection reheat-increasing compressor; determining the actual exhaust superheat according to the outlet water temperature and the exhaust temperature, and determining the evaporation temperature according to the suction pressure; determining a plurality of temperature control stages according to the exhaust temperature; the temperature control stages comprise a low exhaust temperature control stage, a medium exhaust temperature control stage, and a high exhaust temperature control stage; in the low exhaust temperature control stage, controlling the opening of the liquid injection electric regulating valve and the air-injection expansion valve according to the exhaust temperature; in the medium exhaust temperature control stage, determining a plurality of control intervals according to the evaporation temperature, and calculating the target exhaust superheat in each control interval, so as to control the opening of the air-injection expansion valve according to the target exhaust superheat and the actual exhaust superheat; in the high exhaust temperature control stage, controlling the opening of the liquid injection electric regulating valve according to the change trend of the exhaust temperature. The present invention improves the heating capacity of the air source heat pump unit when operating at low ambient temperature; when the unit operates at a large pressure ratio, the problem of excessively high exhaust temperature is effectively controlled to ensure reliable operation of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] Figure 1A schematic diagram of the structure of a low-temperature heat pump system provided by an embodiment of the present invention;

[0040] Figure 2 A flow chart of a method provided by an embodiment of the present invention.

[0041] Description of reference numerals:

[0042] 1-water outlet temperature; 2-exhaust temperature; 3-intake pressure; 4-air expansion valve; 5-liquid injection electric regulating valve. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The purpose of the present invention is to provide a control method for the exhaust temperature of a low-temperature heat pump system, which controls the opening of the air-supply electronic expansion valve according to the exhaust superheat to ensure a reasonable liquid supply demand on the air-supply side. The ideal state is to ensure that the refrigerant at the outlet of the economizer on the air-supply side is saturated steam; the liquid injection electric regulating valve is adjusted according to the exhaust temperature to ensure that the system exhaust temperature is within a reasonable range.

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Figure 1 A schematic diagram of the structure of a low-temperature heat pump system provided in an embodiment of the present invention is shown in FIG. Figure 1As shown, the low-temperature heat pump system of this embodiment includes: an air-injection reheat-increasing compressor, an electronic expansion valve, a shell and tube heat exchanger, a fin heat exchanger, an economizer, a gas-liquid separator, a four-way valve, an air-injection expansion valve 4 and a liquid injection electric regulating valve 5, wherein one end of the air-injection reheat-increasing compressor is connected to a port on one side of the four-way valve; three ports on the other side of the four-way valve are respectively connected to one end of the shell and tube heat exchanger, one end of the fin heat exchanger and one end of the gas-liquid separator; the other end of the fin heat exchanger is connected to the electronic expansion valve 5. The expansion valve is respectively connected to one end of one side of the economizer, one end of the air-inflation expansion valve 4 and one end of the liquid-injection electric regulating valve 5; the other end of the shell-and-tube heat exchanger is connected to the other end of one side of the economizer; the other end of the air-inflation re-enthalpy increasing compressor is connected to the other end of the gas-liquid separator; one end of the other side of the economizer is respectively connected to another end of the air-inflation re-enthalpy increasing compressor and the other end of the liquid-injection electric regulating valve 5; the other end of the other side of the economizer is connected to the other end of the air-inflation expansion valve 4. The shell-and-tube heat exchanger also has one end for water outlet, and this embodiment obtains its outlet water temperature 1 through this end. This embodiment also collects the suction pressure 3 at the inlet of the air-inflation re-enthalpy increasing compressor.

[0047] For example, the liquid injection electric regulating valve 5 of this embodiment is electrically regulated to control the size and direction of the valve opening and closing according to the trend and amplitude of the exhaust temperature 2 change.

[0048] Specifically, the present embodiment also includes an air supply and liquid injection control system, and the system includes: a heating condenser water outlet temperature sensor, an intake pressure sensor, an exhaust temperature sensor, and a unit controller to control the output of two 0-10V analog signals to respectively control the opening of the air supply expansion valve and the liquid injection electric regulating valve.

[0049] like Figure 2 As shown, the control method of this embodiment includes:

[0050] Step 100: when the air-injection reheat increasing compressor is in the working state under the heating model, the exhaust gas temperature at the outlet of the air-injection reheat increasing compressor, the outlet water temperature of the shell and tube heat exchanger, and the suction pressure at the inlet of the air-injection reheat increasing compressor are obtained;

[0051] Step 200: determining the actual exhaust superheat according to the outlet water temperature and the exhaust temperature, and determining the evaporation temperature according to the suction pressure;

[0052] Step 300: determining a plurality of temperature control stages according to the exhaust temperature; the temperature control stages include a low exhaust temperature control stage, a medium exhaust temperature control stage and a high exhaust temperature control stage;

[0053] Step 400: In the low exhaust temperature control stage, the openings of the liquid injection electric regulating valve and the air supplement expansion valve are controlled according to the exhaust temperature;

[0054] Step 500: In the middle exhaust temperature control stage, multiple control intervals are determined according to the evaporation temperature, and the target exhaust superheat in each control interval is calculated to control the opening of the air supplement expansion valve according to the target exhaust superheat and the actual exhaust superheat;

[0055] Step 600: In the high exhaust temperature control stage, the opening of the liquid injection electric regulating valve is controlled according to the variation trend of the exhaust temperature.

[0056] Optionally, the algorithm for calculating the exhaust superheat is to add ΔT to the condenser outlet water temperature to calculate the condensation temperature, and then subtract the calculated condensation temperature from the exhaust temperature to obtain the value of the exhaust superheat. For example, ΔT is the heat exchange end difference, which is fixed at 5 degrees and can be adjusted according to the actual heat exchange conditions of the heat exchanger.

[0057] Specifically, the algorithm for calculating the evaporation temperature is the saturation temperature corresponding to the suction pressure; the suction pressure in this embodiment is a measured value, that is, the suction pressure is obtained through measurement.

[0058] Furthermore, the system of this embodiment adds control of the air supplement expansion valve and the liquid injection electric regulating valve when the compressor is in operation.

[0059] Furthermore, the specific control ideas of this embodiment are as follows:

[0060] First, the temperature control system is divided into three control stages according to the exhaust temperature, namely, the low exhaust temperature control stage T 排气 <T1; in the middle exhaust temperature control stage, T1≤T 排气 <T2; High exhaust temperature control stage T 排气 ≥ T2. For example, T1 and T2 are obtained through experiments and can be used as fixed values ​​in this embodiment, that is, T1 = 90°C; T2 = 105°C, which can be adjusted according to actual operating conditions.

[0061] (1) Low exhaust temperature control stage:

[0062] When the system starts, the system is in the low exhaust temperature control range T 排气 <T1, the liquid injection electric regulating valve is in the closed state, at this time, an initial opening is given to the air supply expansion valve, and this opening is a fixed opening.

[0063] (2) Middle exhaust temperature control stage:

[0064] When the system is in the middle exhaust temperature control stage T1≤T 排气 <T2, the system enters the air expansion valve adjustment control stage. In this control range, the system can correspond to different target exhaust superheat according to different evaporation temperature ranges. The ranges are divided as follows

[0065] Evaporation temperature control range 1: T蒸发 <T setp01 Target exhaust superheat 1;

[0066] Evaporation temperature control range 2: T setp01 ≤T 蒸发 <T setp02 Target exhaust superheat 2;

[0067] Evaporation temperature control range 3: T setp02 ≤T 蒸发 <T setp03 Target exhaust superheat 3;

[0068] Evaporation temperature control range 4: T 蒸发 >T setp03 Target exhaust superheat 4;

[0069] Specifically, this embodiment measures the value of the exhaust superheat corresponding to the evaporation temperature under the optimal COP based on experiments, and fits the corresponding curve and polynomial based on the test data. Since one polynomial cannot meet the requirements of the entire control range, the inflection point of the curve is the basis for segmentation. In this embodiment, it can be set to a fixed value, that is, T setp01 =-17.5℃; T setp02 =-12.5℃; T setp03 =-2.5℃.

[0070] The exhaust superheat is divided into different control intervals according to different evaporation temperatures. Each control interval corresponds to a different target superheat setting value. The actual exhaust superheat of each section is used as the control variable. The opening of the output air expansion valve is adjusted through the PID control method. The control signal is a 0-10V voltage signal.

[0071] Algorithm for target superheat: The exhaust superheat value corresponding to the optimal COP is measured at different condensing temperatures within each evaporation temperature range through experiments, so as to fit the relationship between the exhaust superheat and the condensing temperature.

[0072] The actual control value of the exhaust superheat in each evaporation temperature control range, that is, the target exhaust superheat, can be calculated through the relationship. When the actual exhaust superheat is greater than the target exhaust superheat, the air expansion valve is opened wide, and when the actual exhaust superheat is less than the target exhaust superheat, the air expansion valve is closed narrowly.

[0073] The following describes the algorithm for the target exhaust superheat during the exhaust temperature control stage through an example.

[0074] Through experimental measurement:

[0075] Evaporation temperature control range 1: T 蒸发 <-17.5, at 30℃≤T 冷凝The exhaust superheat values ​​corresponding to different condensing temperatures under the optimal COP were measured in the range of ≤50.0℃, and the calculation formula for the optimal superheat corresponding to the evaporation temperature was fitted: y=0.008x 2 +0.08x+36.9;

[0076] Evaporation temperature control range 2: -17.5℃≤T 蒸发 <-12.5℃, at 30℃≤T 冷凝 The exhaust superheat values ​​corresponding to different condensing temperatures under the optimal COP were measured in the range of ≤55.0℃, and the calculation formula for the optimal superheat corresponding to the evaporation temperature was fitted: y=0.006x 2 +0.198x+29.57;

[0077] Evaporation temperature control range 3: -7.5℃≤T 蒸发 <-2.5℃, at 30℃≤T 冷凝 The exhaust superheat values ​​corresponding to different condensing temperatures under the optimal COP were measured in the range of ≤60.0℃, and the calculation formula for the optimal superheat corresponding to the evaporation temperature was fitted: y=0.002x 2 +0.43x+19;

[0078] Evaporation temperature control range 4: T 蒸发 ≥-2.5℃, at 30℃≤T 冷凝 The exhaust superheat values ​​corresponding to different condensing temperatures under the optimal COP were measured in the range of ≤62.5℃, and the calculation formula for the optimal exhaust superheat corresponding to the evaporation temperature was fitted: y=0.56x+12.1;

[0079] In the above formula, x is the evaporation temperature and y is the exhaust superheat.

[0080] (3) High exhaust temperature control stage

[0081] When the system is in the high exhaust temperature control stage T 排气 >T2, the system enters the control stage of the liquid injection electric regulating valve.

[0082] T 排气 = T2, the air expansion valve is fully open, and the electric regulating valve of the liquid injection valve is fully closed. To avoid the sudden change of the exhaust temperature, which may cause the system to run unstably, the electric valve of the liquid injection valve adopts proportional regulation, that is, when T 排气 >T2, in each detection cycle (settable), the system determines the change of exhaust temperature once, and controls the direction of the switch of the liquid injection electric regulating valve according to the temperature change trend; at the same time, the size of the switch of the liquid injection electric regulating valve is adjusted according to the amplitude of the exhaust temperature change.

[0083] The specific operation method is: when the temperature difference between the exhaust temperature read in two adjacent detection cycles is greater than T Dset When the exhaust temperature is less than T in two detection cycles, the electric control valve of the liquid injection needs to enter the fast adjustment stage, and the adjustment range of each adjustment cycle is A%. Dset -T Diff When , it is determined that the liquid injection electric regulating valve needs to enter the slow adjustment stage, and the adjustment range of each adjustment cycle is B%. For example, T Dset It is obtained by testing and can be adjusted according to the actual operation. In this embodiment, it is set to a fixed value, T Dset =5°C; the values ​​of A and B are obtained through testing, with the purpose of preventing the exhaust temperature from rising continuously after the injection regulating valve participates in the regulation. They can be adjusted according to the actual operation. In this embodiment, they can be determined as fixed values, i.e., A=8%, B=3%; T Diff This is to avoid jumps in the control value at a fixed temperature, and can be adjusted according to actual operating conditions. Diff Determined as a fixed value, T Diff =3℃.

[0084] Specifically, the entire control system of this embodiment is divided into three control stages according to the exhaust temperature. By adjusting different system equipment, not only the purpose of air supplement and enthalpy increase is achieved, but also the exhaust temperature of the system is controlled within a safe range; the control stage of air supplement and enthalpy increase adds an algorithm for the exhaust superheat corresponding to the optimal COP, which is a multi-stage control; and in the high exhaust temperature control stage, the liquid injection valve adopts an electric regulating valve, which adopts a proportional regulation method. In addition, the system divides the control of the liquid injection electric regulating valve into two adjustment modes, fast and slow, by judging the amplitude of the exhaust temperature change, effectively avoiding the exhaust temperature jump caused by traditional switch control, which leads to unstable system operation.

[0085] The beneficial effects of the present invention are as follows:

[0086] (1) The present invention improves the heating capacity of the air source heat pump unit under low ambient temperature operation;

[0087] (2) When the unit is operating at a large pressure ratio, the present invention can effectively control the problem of excessive exhaust temperature and ensure the reliable operation of the unit.

[0088] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0089] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for controlling the exhaust temperature of a low-temperature heat pump system, characterized in that: The low-temperature heat pump system includes: an air-injection reheat compressor, an electronic expansion valve, a shell and tube heat exchanger, a fin heat exchanger, an economizer, a gas-liquid separator, a four-way valve, an air-injection expansion valve and a liquid injection electric regulating valve, wherein one end of the air-injection reheat compressor is connected to a port on one side of the four-way valve; three ports on the other side of the four-way valve are respectively connected to one end of the shell and tube heat exchanger, one end of the fin heat exchanger and one end of the gas-liquid separator; the other end of the fin heat exchanger is respectively connected to one end of one side of the economizer, one end of the air-injection expansion valve and one end of the liquid injection electric regulating valve through the electronic expansion valve; the other end of the shell and tube heat exchanger is connected to the other end of one side of the economizer; the other end of the air-injection reheat compressor is connected to the other end of the gas-liquid separator; one end of the other side of the economizer is respectively connected to another end of the air-injection reheat compressor and the other end of the liquid injection electric regulating valve; the other end of the other side of the economizer is connected to the other end of the air-injection expansion valve; the control method includes: When the air-injection reheat-increasing compressor is in a working state under a heating model, the exhaust temperature at the outlet of the air-injection reheat-increasing compressor, the outlet water temperature of the shell and tube heat exchanger, and the suction pressure at the inlet of the air-injection reheat-increasing compressor are obtained; determining an actual exhaust superheat according to the outlet water temperature and the exhaust temperature, and determining an evaporation temperature according to the suction pressure; Determine a plurality of temperature control stages according to the exhaust temperature; the temperature control stages include a low exhaust temperature control stage, a medium exhaust temperature control stage and a high exhaust temperature control stage; In the low exhaust temperature control stage, the openings of the liquid injection electric regulating valve and the air supplement expansion valve are controlled according to the exhaust temperature; In the middle exhaust temperature control stage, a plurality of control intervals are determined according to the evaporation temperature, and a target exhaust superheat in each control interval is calculated, so as to control the opening of the air supplement expansion valve according to the target exhaust superheat and the actual exhaust superheat; In the high exhaust temperature control stage, the opening of the liquid injection electric regulating valve is controlled according to the change trend of the exhaust temperature.

2. The method for controlling the exhaust temperature of a low-temperature heat pump system according to claim 1, characterized in that: Determining the actual exhaust gas superheat according to the outlet water temperature and the exhaust gas temperature includes: Add the water outlet temperature to the preset temperature to calculate the condensation temperature; The actual exhaust gas superheat is obtained by subtracting the estimated condensation temperature from the exhaust gas temperature.

3. The method for controlling the exhaust temperature of a low-temperature heat pump system according to claim 1, characterized in that: Determining the evaporation temperature according to the suction pressure includes: The saturation temperature corresponding to the suction pressure is determined as the evaporation temperature.

4. The method for controlling the exhaust temperature of a low-temperature heat pump system according to claim 1, characterized in that: A plurality of temperature control stages are determined according to the exhaust gas temperature, including: When the exhaust temperature meets T 排气 <T1, the current temperature control stage is determined as the low exhaust temperature control stage; When the exhaust temperature meets T1≤T 排气 <T2, the current temperature control stage is determined as the middle exhaust temperature control stage; When the exhaust temperature meets T 排气 ≥T2, the current temperature control stage is determined as the high exhaust temperature control stage; wherein, T 排气 is the exhaust temperature; T1 is the threshold temperature of the first temperature control stage, and T2 is the threshold temperature of the second temperature control stage.

5. The method for controlling the exhaust temperature of a low-temperature heat pump system according to claim 1, characterized in that: In the low exhaust temperature control stage, the openings of the liquid injection electric regulating valve and the air supplement expansion valve are controlled according to the exhaust temperature, including: The working state of the liquid injection electric regulating valve is adjusted to a closed state, and at the same time, an initial opening is set for the air replenishment expansion valve, and the initial opening is set to a fixed opening.

6. The method for controlling the exhaust temperature of a low-temperature heat pump system according to claim 1, characterized in that: The calculation process of the target exhaust superheat includes: The exhaust superheat value corresponding to the optimal refrigeration coefficient at different condensing temperatures in each control range is measured through a preset experiment; According to the corresponding exhaust superheat value, the relationship between the exhaust superheat and the condensation temperature is fitted; The target exhaust gas superheat is determined according to a relationship between the exhaust gas superheat and the condensation temperature.

7. The method for controlling the exhaust temperature of a low-temperature heat pump system according to claim 1, characterized in that: Controlling the opening of the air supplement expansion valve according to the target exhaust gas superheat and the actual exhaust gas superheat includes: When the actual exhaust gas superheat is greater than the target exhaust gas superheat, the opening of the air supplement expansion valve is controlled to increase through a PID control method; When the actual exhaust gas superheat is less than the target exhaust gas superheat, the opening of the air supplement expansion valve is controlled to decrease through PID control.

8. The method for controlling the exhaust temperature of a low-temperature heat pump system according to claim 1, characterized in that: In the high exhaust temperature control stage, the opening of the liquid injection electric regulating valve is controlled according to the change trend of the exhaust temperature, including: When the temperature difference between the exhaust temperatures read in two adjacent detection cycles is greater than a preset first temperature difference trend threshold temperature, it is determined that the liquid injection electric regulating valve enters a fast regulation stage, and the regulation amplitude of each regulation cycle is A%; When the temperature difference between the exhaust temperatures read in two detection cycles is less than the preset second temperature difference trend threshold temperature, it is determined that the liquid injection electric control valve needs to enter the slow adjustment stage, and the adjustment amplitude of each adjustment cycle is B%; wherein A is the first preset adjustment amplitude, and B is the second preset adjustment amplitude; A>B.

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