A method for controlling the opening degree of an expansion valve in the frequency rising of a heat pump host and a heat pump system

Abstract

The present application relates to a kind of expansion valve opening degree control method in the frequency of heat pump host starting, comprising the following steps: obtaining the return water temperature and ambient temperature of heat pump system starting, and the reference opening degree of expansion valve of heat pump host starting is obtained by correcting return water temperature and ambient temperature;Every interval valve period obtains the compressor frequency value of current heat pump host, and the current compressor frequency rise value is calculated according to the compressor frequency value of last valve period;Compressor frequency rise value is corrected;The current opening degree value of expansion valve is determined according to the reference opening degree of expansion valve, the corrected compressor frequency rise value and frequency variation coefficient.The expansion valve opening degree control method of heat pump host starting of the present application can make the setting of expansion valve opening degree more comply with the variation of system refrigerant flow under different frequency in compressor starting stage, make the control of refrigerant flow more accurate, can effectively avoid the problem that expansion valve opening degree and system refrigerant flow are extremely mismatched in unit starting stage, to avoid the problem that compressor appears back liquid phenomenon.

Description

Technical Field

[0001] This invention relates to the field of heat pumps, and more particularly to a method for controlling the opening degree of the expansion valve and a heat pump system during the start-up and frequency increase of a heat pump host. Background Technology

[0002] Existing air source heat pump units typically set a baseline opening for the expansion valve during initial startup to ensure normal operation. The accuracy of this baseline opening directly impacts the system's stability and energy efficiency. An inappropriate baseline opening can affect unit operation, potentially leading to liquid and oil return risks, compromising reliability, and posing safety hazards, especially in applications with frequent start-ups and shutdowns, thus increasing the probability of unit burnout.

[0003] Currently, most inverter systems operate by setting the unit to a fixed baseline opening degree (a fixed expansion valve opening degree at the initial startup). In heating mode, after the compressor starts, it will adjust its operation according to the ambient temperature (T). E ) and return water temperature (T RW The opening value of the expansion valve is determined by the range of ambient and return water temperatures to meet the basic operating requirements of the unit. Table 1 shows preset expansion valve opening values ​​based on the corresponding ambient and return water temperatures (confirmed by laboratory tests). These are initial values ​​for the corresponding ambient and return water temperature ranges and are not as precise as refrigerant flow control. Because the optimal refrigerant flow control varies under different ambient and return water temperatures, the corresponding expansion valve opening values ​​also differ.

[0004] Table 1. Reference opening degree of expansion valve during common start-up phases

[0005]

[0006] On the other hand, please see Figure 1 Because the compressor needs to maintain two frequency points for 1 to 2 minutes each during startup, the common compressor frequency increase logic during unit startup is as follows:

[0007] 1) When the target frequency is less than platform 1, the compressor frequency is increased to platform 1 and run for 1 to 2 minutes, then reduced to the target frequency;

[0008] 2) When the target frequency is greater than or equal to platform 1 and less than platform 2, the compressor frequency is increased to platform 1 and run for 1 to 2 minutes before being increased to the target frequency;

[0009] 3) When the target frequency is greater than or equal to platform 2, the compressor frequency is raised to platform 1 and run for 1 minute, then raised to platform 2 and run for 1 to 2 minutes, and then raised to the target frequency.

[0010] The compressor starts and runs in the first platform, according to the reference opening table shown in Table 1. After the first platform is completed, it enters PID regulation control. During this process, the compressor frequency gradually increases and the refrigerant circulation volume also increases. However, the expansion valve opening is always a fixed reference opening. At this time, the system refrigerant flow rate and the expansion valve opening are extremely mismatched, and the compressor is very likely to have a liquid return problem.

[0011] Therefore, it is necessary to study how to accurately control the opening of the expansion valve during the compressor start-up and frequency ramp-up phase to match it with the required refrigerant flow and avoid liquid return problems in the compressor. Summary of the Invention

[0012] Based on this, the purpose of the present invention is to provide a method for controlling the opening degree of the expansion valve during the start-up and frequency increase of a heat pump host. By precisely controlling the opening degree of the expansion valve during the start-up and frequency increase stage of the compressor, the refrigerant flow can be precisely controlled to meet the target frequency requirements and avoid the compressor from experiencing liquid return problems.

[0013] A method for controlling the opening degree of the expansion valve during the start-up and frequency increase of a heat pump host includes the following steps:

[0014] S10 obtains the return water temperature T when the heat pump system starts up. RW and ambient temperature T E and the return water temperature T RW and ambient temperature T E Make corrections, and based on the corrected return water temperature T RW and ambient temperature T E Determine the reference opening degree C1 of the expansion valve;

[0015] S20 obtains the current compressor frequency value F of the heat pump host at intervals of Δt. N And based on the compressor frequency value F of the previous valve control cycle L The current compressor frequency rise value ΔF is calculated, where Δt is one valve control cycle;

[0016] S30 corrects the compressor frequency rise value ΔF to obtain the corrected compressor frequency rise value ΔF′.

[0017] S40 calculates the current opening value C1′ of the expansion valve based on the reference opening degree C1 of the expansion valve, the frequency rise value ΔF′ of the corrected compressor, and the frequency change coefficient Q.

[0018] Furthermore, the current opening value C1′ of the expansion valve described in step S40 satisfies the following relationship:

[0019] C1′=Q*ΔF′+C1

[0020] In the formula, ΔF′ represents the corrected compressor frequency rise value, Q is the frequency change coefficient, and C1 represents the reference opening degree of the expansion valve.

[0021] Furthermore, the frequency variation coefficient Q is determined in the following manner:

[0022] When the frequency rise of adjacent valve control cycles is less than 48Hz, the frequency change coefficient Q = 1;

[0023] When the frequency rise of adjacent valve control cycles is greater than or equal to 48Hz and less than 65Hz, the frequency change coefficient Q = 1.5.

[0024] When the frequency increase of adjacent valve control cycles is greater than 65Hz, the frequency change coefficient Q = 2.

[0025] Furthermore, the reference opening degree C1 of the expansion valve described in step S10 satisfies the following relationship:

[0026] C1 = MAX[a*T] R ′ W ,0]+MAX[b*T E ′,0]+c1

[0027] In the formula, T R ′ W This indicates the corrected return water temperature, where 'a' represents the control coefficient for the corrected return water temperature, and 'T' represents the control coefficient for the corrected return water temperature. E ′ represents the corrected ambient temperature, b represents the control coefficient for correcting the ambient temperature, c1 represents the compensation value for the reference opening of the expansion valve, and MAX represents the function that takes the maximum value.

[0028] Compared with the prior art, the present invention uses the obtained current compressor frequency value F of the heat pump host. N Compressor frequency value F of the previous valve control cycle L The difference is combined with the frequency variation coefficient to fine-tune the reference opening of the compressor start-up expansion valve; this makes the setting of the expansion valve opening more consistent with the changes in the system refrigerant flow at different frequencies during the compressor start-up stage, making the control of refrigerant flow more precise, effectively avoiding the problem of extreme mismatch between the expansion valve opening and the system refrigerant flow during the unit start-up stage, and thus avoiding the problem of liquid return in the compressor.

[0029] Meanwhile, the present invention also provides a heat pump system, including a compressor, a condenser, an expansion valve, an evaporator, a water circulation unit, and a control unit. The compressor, condenser, expansion valve, and evaporator are sequentially connected in a refrigerant pipeline. The water circulation unit is connected to the condenser via a water pipeline. The control unit is electrically connected to the compressor and the expansion valve. The control unit includes a temperature measuring component and a controller. The temperature measuring component collects the ambient temperature and the return water temperature of the water circulation unit and transmits the collected temperature signals to the controller. The controller collects the frequency signal of the compressor and calculates the current opening value of the expansion valve using the above-mentioned expansion valve opening control method program stored on the controller. Then, it sends a signal to the expansion valve to adjust the opening, thereby controlling the opening adjustment of the expansion valve.

[0030] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the compressor's frequency ramp-up mode when the heat pump unit is turned on in the existing technology;

[0032] Figure 2 A schematic diagram of a heat pump system to which the control method for the opening of the expansion valve during the start-up and frequency increase of the heat pump host is applicable;

[0033] Figure 3 A flowchart illustrating the control method for the opening degree of the expansion valve during the start-up and frequency increase of a heat pump main unit. Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings of the embodiments of the present invention.

[0035] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; and the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0036] In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only for distinction and not to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0037] To address the mismatch between the reference opening of the expansion valve controlling the refrigerant flow of the compressor and the refrigerant flow required for the compressor frequency to increase during the start-up of a heat pump unit, this invention provides a method for controlling the opening of the expansion valve during the frequency increase of a heat pump unit. This control method is not limited to scenarios such as heat pump water heaters and heat pump floor heating; it can be applied to main units involving variable frequency systems.

[0038] For specific implementation details, please refer to [link / reference]. Figure 2 When the expansion valve opening control method during the start-up and frequency increase of a heat pump host is applied to a heat pump system, the heat pump system includes a compressor 10, a condenser 20, an expansion valve 30, an evaporator 40, a water circulation unit 50, and a control unit 60. The compressor 10, condenser 20, expansion valve 30, and evaporator 40 are sequentially connected via refrigerant piping; the water circulation unit 50 is connected to the condenser 20 via a water piping; and the control unit 60 is electrically connected to the compressor 10 and the expansion valve 30.

[0039] Specifically, the exhaust port 11 of the compressor 10 is connected to the return port 12 of the compressor 10 via the condenser 20, expansion valve 30, and evaporator 40 in sequence, forming a refrigerant circulation pipeline. Water supplied by the water tank 51 of the water circulation unit 50 enters the inlet pipe 52 and passes through the condenser 20, absorbing the heat released during the condensation of the high-temperature refrigerant. After releasing heat in the water pipe 53, the water returns to the water tank 51 via the return pipe 54, forming a water circulation pipeline. The control unit 60 includes a temperature measuring component 61 and a controller 62. The temperature measuring component 61 includes a first temperature sensor 611 and a second temperature sensor 612. The first temperature sensor 611, the second temperature sensor 612, the compressor 10, and the expansion valve 30 are electrically connected to the controller 62. The first temperature sensor 611 is installed at the port of the return water pipe 54 entering the water tank 51 to detect the return water temperature and transmit the return water temperature signal to the controller 63; the second temperature sensor 612 is used to detect the ambient temperature and transmit the ambient temperature signal to the controller 63; the controller 63 is used to receive the temperature signals from the first temperature sensor 611 and the second temperature sensor 612 and the frequency signal from the compressor 10, and after calculating the current opening value of the expansion valve 30 through the program of the start-up frequency increase expansion valve opening control method stored on the controller 63, it sends a signal to the expansion valve 30 to adjust the opening and control the opening adjustment of the expansion valve 30.

[0040] The expansion valve opening control method provided by this invention mainly controls the expansion valve opening of the variable frequency compressor during the following stages of frequency increase:

[0041] 1) The compressor frequency starts from 0Hz and increases to the first platform, and runs at the platform frequency for 1 to 2 minutes. The frequency of the first platform is between 40Hz and 60Hz.

[0042] 2) The compressor continuously increases its frequency to the second platform and runs at the platform frequency for 1 to 2 minutes. The frequency of the second platform is between 70 Hz and 90 Hz.

[0043] 3) The compressor continues to increase its frequency to the target frequency, completing the unit's start-up frequency increase phase.

[0044] The expansion valve opening control in the subsequent stages of the compressor is implemented by a PID controller, which controls the expansion valve.

[0045] Please see Figure 3 The method for controlling the opening degree of the expansion valve during the start-up and frequency increase of a heat pump host provided by the present invention includes the following steps:

[0046] S10 obtains the return water temperature T when the heat pump system starts up. RW and ambient temperature T E and the return water temperature T RW and ambient temperature T EMake corrections, and based on the corrected return water temperature T RW and ambient temperature T E Determine the reference opening degree C1 of the expansion valve;

[0047] S20 obtains the current compressor frequency value F of the heat pump unit at intervals of Δt. N And based on the compressor frequency value F of the previous valve control cycle L The current compressor frequency rise value ΔF is calculated, where Δt is one valve control cycle;

[0048] S30 corrects the compressor frequency rise value ΔF to obtain the corrected compressor frequency rise value ΔF′.

[0049] S40 calculates the current opening value C1′ of the expansion valve based on the reference opening degree C1 of the expansion valve, the frequency rise value ΔF′ of the corrected compressor, and the frequency change coefficient Q.

[0050] In a specific embodiment, in step S10, a fixed-value compensation method is used to adjust the return water temperature T. RW Corrected to T R ′ W , making T R ′ W =T RW -B; Set the ambient temperature T E Corrected to T E ′, making T E ′=-(T E -C). Further, the return water temperature T RW The compensation value B is set to 7; the ambient temperature T E The compensation value C is set to 30.

[0051] The maximum value is used to adjust the return water temperature T. R ′ W and corrected ambient temperature T E The reference opening degree C1 of the expansion valve is determined. The reference opening degree C1 is the initial opening degree when the unit is started, and its value satisfies the following relationship:

[0052] C1 = MAX[a*T] R ′ W ,0]+MAX[b*T E [′,0]+c1 (1)

[0053] (1) In the formula, a represents the control coefficient for correcting the return water temperature, b represents the control coefficient for correcting the ambient temperature, and c1 represents the compensation value for the reference opening of the expansion valve. Among them, a and b are the experimental verification parameters of the unit.

[0054] Furthermore, the control coefficient 'a' for correcting the return water temperature ranges from 0.5 to 2; the control coefficient 'b' for correcting the ambient temperature ranges from 0.5 to 2; and the compensation value 'c1' for the expansion valve reference opening is defined based on the flow curve of different electronic expansion valves, with a conventional compensation value 'c1' of 55.

[0055] In step S20, the compressor frequency increase ΔF satisfies ΔF = F N -F L F L This indicates the frequency value acquired by the compressor during the previous valve adjustment cycle of the corresponding expansion valve. Further, the valve adjustment cycle of the expansion valve is set to T = 5s during the start-up phase, and then to T = 20s thereafter.

[0056] In step S30, a fixed-value compensation method is used to correct the compressor frequency increase ΔF to ΔF′, so that ΔF′=ΔF-A. Further, the fixed value of the compensation value A for the compressor frequency increase ΔF is 2.

[0057] In step S40, the current opening value C1′ of the expansion valve is calculated by linear addition using the reference opening value C1 of the expansion valve, the corrected compressor frequency rise value ΔF′, and the frequency change coefficient Q. The current opening value C1′ of the expansion valve satisfies the following relationship:

[0058]

[0059] (2) In the formula, Q is the frequency variation coefficient.

[0060] Furthermore, this application determines the value of the frequency change coefficient Q based on the range of frequency rise values ​​in adjacent valve control cycles, specifically as follows:

[0061] When the frequency rise of adjacent valve control cycles is less than 48Hz, the frequency change coefficient Q = 1;

[0062] When the frequency rise of adjacent valve control cycles is greater than or equal to 48Hz and less than 65Hz, the frequency change coefficient Q = 1.5.

[0063] When the frequency increase of adjacent valve control cycles is greater than 65Hz, the frequency change coefficient Q = 2.

[0064] As shown in Table 2.

[0065] Table 2

[0066] Frequency rise range <48(Hz) 48–65 (Hz) >65 (Hz) Q value 1 1.5 2

[0067] For example, when the ambient temperature T E The temperature is 14℃, and the return water temperature is T. RWAt 35℃, with A = 7, B = 30, a = 1.2, b = 0.8, and c1 = 55, calculate the reference opening C1 of the expansion valve:

[0068] C1=55+MAX[1.2*(14-7),0]+MAX[0.8*(30-35),0]=63.4.

[0069] When the compressor is started, its frequency increases from 0Hz in the initial valve control cycle to 10Hz, corresponding to a compressor frequency increase ΔF of 10. According to the frequency increase range in Table 2, the frequency change coefficient Q = 1 for 40Hz. Taking C = 2, calculate the current opening degree C1′ of the expansion valve:

[0070] C1′=1*(10-2)+63.4=71.4.

[0071] When the ambient temperature T E The temperature is 14℃, and the return water temperature is T. RW At 35°C, the reference opening value of the expansion valve during the start-up and frequency increase of a heat pump unit in existing technology can be referenced from Table 1, where the reference opening value is 3371. This reference opening value is determined based on the current highest frequency of the heat pump unit. Compared with the reference opening value in Table 1, the method provided by this invention calculates the reference opening value of the expansion valve, which can more accurately control the opening of the expansion valve during the start-up and frequency increase of the heat pump unit. Furthermore, the opening of the expansion valve can be adjusted in a matching manner according to the change of compressor frequency, so that the change of refrigerant flow matches the change of the unit frequency.

[0072] The method of this invention is based on the obtained current compressor frequency value F of the heat pump host. N Compressor frequency value F of the previous valve control cycle L The difference is combined with the frequency variation coefficient to fine-tune the reference opening of the compressor start-up expansion valve; this makes the setting of the expansion valve opening more consistent with the changes in the system refrigerant flow at different frequencies during the compressor start-up stage, making the control of refrigerant flow more precise, effectively avoiding the problem of extreme mismatch between the expansion valve opening and the system refrigerant flow during the unit start-up stage, and thus avoiding the problem of liquid return in the compressor.

[0073] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A method for controlling the opening degree of the expansion valve during the start-up and frequency increase of a heat pump main unit, characterized in that, Includes the following steps: S10 obtains the return water temperature T when the heat pump system starts up. RW and ambient temperature T E and the return water temperature T RW and ambient temperature T E Make corrections, and based on the corrected return water temperature T RW and ambient temperature T E Determine the reference opening degree C1 of the expansion valve, where C1 satisfies the following relationship: C1=MAX[a*T′ RW ,0]+MAX[bT′ E ,0]+c1 In the formula, T′ RW This indicates the corrected return water temperature, where 'a' represents the control coefficient for the corrected return water temperature, and T′ represents the corrected return water temperature. E denoted as 'b', which represents the control coefficient for correcting the ambient temperature; denoted as 'c1', which represents the compensation value for the reference opening of the expansion valve; and 'MAX', which represents the function that takes the maximum value. S20 obtains the current compressor frequency value F of the heat pump host at intervals of Δt. N And based on the compressor frequency value F of the previous valve control cycle L The current compressor frequency rise value ΔF is calculated, where Δt is one valve control cycle; S30 corrects the compressor frequency rise value ΔF to obtain the corrected compressor frequency rise value ΔF′. S40 calculates the current opening value C1′ of the expansion valve based on the reference opening degree C1 of the expansion valve, the frequency rise value ΔF′ of the corrected compressor, and the frequency change coefficient Q.

2. The control method according to claim 1, characterized in that, The compressor frequency increase ΔF mentioned in step S20 satisfies the following formula: ΔF=F N -F L In the formula, F N This indicates the current compressor frequency value of the heat pump unit, F. L This indicates the compressor frequency value of the heat pump unit in one valve adjustment cycle; The valve control cycle is set to Δt = 5 seconds during the start-up phase and Δt = 20 seconds thereafter.

3. The control method according to claim 2, characterized in that, In step S30, a fixed-value compensation method is used to correct the compressor frequency rise ΔF. The corrected compressor frequency rise ΔF′ satisfies the following formula: ΔF′=ΔF-A In the formula, A represents the compensation value for the increase in compressor frequency.

4. The control method according to any one of claims 1-3, characterized in that, The current opening value C1′ of the expansion valve mentioned in step S40 satisfies the following relationship: C1′=Q*ΔF′+C1 In the formula, ΔF′ represents the corrected compressor frequency rise value, Q is the frequency change coefficient, and C1 represents the reference opening degree of the expansion valve.

5. The control method according to claim 4, characterized in that, The frequency variation coefficient Q is determined in the following manner: When the frequency rise of adjacent valve control cycles is less than 48Hz, the frequency change coefficient Q = 1; When the frequency rise of adjacent valve control cycles is greater than or equal to 48Hz and less than 65Hz, the frequency change coefficient Q = 1.

5. When the frequency increase of adjacent valve control cycles is greater than 65Hz, the frequency change coefficient Q = 2.

6. The control method according to claim 1, characterized in that, In step S10, a fixed-value compensation method is used to adjust the return water temperature T. RW and ambient temperature T E The correction is made, specifically the correction of the return water temperature T′. RW Represented as: T′ RW =T RW -B In the formula, B represents the return water temperature T. RW The compensation value; The corrected ambient temperature T E ′ is represented as: T E ′=-(T E -C) In the formula, C represents the ambient temperature T. E The compensation value.

7. The control method according to claim 1, characterized in that, The control coefficient 'a' for correcting the return water temperature ranges from 0.5 to 2; the control coefficient 'b' for correcting the ambient temperature ranges from 0.5 to 2.

8. A heat pump system, comprising a compressor, a condenser, an expansion valve, an evaporator, a water circulation unit, and a control unit, wherein the compressor, condenser, expansion valve, and evaporator are sequentially connected via refrigerant piping; the water circulation unit is connected to the condenser via a water piping; and the control unit is electrically connected to the compressor and the expansion valve; characterized in that, The control unit includes a temperature measuring component and a controller. The temperature measuring component collects the ambient temperature and the return water temperature of the water circulation unit and transmits the collected temperature signals to the controller. The controller collects the frequency signal of the compressor and calculates the current opening value of the expansion valve in the heat pump host start-up frequency rise control method as described in any one of claims 1-7 through a program stored on the controller. Then, it sends a signal to the expansion valve to adjust the opening, thereby controlling the opening adjustment of the expansion valve.

9. The heat pump system according to claim 8, characterized in that, The temperature measuring component includes a first temperature sensor and a second temperature sensor. The first temperature sensor is installed in the return water pipe of the water circulation unit to detect the return water temperature and transmit the return water temperature signal to the controller. The second temperature sensor is used to detect the ambient temperature and transmit the ambient temperature signal to the controller.

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