An electronic expansion valve control method based on frequency change rate and heat pump system

Abstract

The present invention relates to an electronic expansion valve control method based on the frequency change rate. The control method corrects the frequency change value by using the frequency and the correction coefficient of the electronic expansion valve to thereby calculate the frequency change rate, and calculates the slope by using the characteristic relationship curve of the refrigerant mass flow rate and the electronic expansion valve opening degree. The electronic expansion valve opening degree is corrected by using the slope and the frequency change rate to obtain the electronic expansion valve target opening degree corresponding to the compressor frequency reduction or increase. The control method overcomes the problem of inaccurate matching between frequency and opening degree caused by calculating and controlling the target opening degree of the electronic expansion valve according to the compressor frequency change in the prior art, eliminates the influence of low ambient temperature and high ambient temperature on the refrigerant mass flow rate, and enables the electronic expansion valve to make more reasonable adjustments according to the current electronic expansion valve opening degree when the heat pump system copes with low ambient temperature and high ambient temperature working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pump control, and in particular to an electronic expansion valve control method based on frequency change rate and a heat pump system. Background Art

[0002] A heat pump system is a highly efficient and environmentally friendly energy utilization technology. Its core operating principle is the reverse Carnot cycle. By consuming a small amount of electricity or other energy, it transfers heat energy from a low-temperature heat source to a high-temperature environment, achieving heating or cooling. Air-source heat pump systems, as a type of heat pump system, absorb low-temperature heat energy from the air using minimal electricity, compress it into high-temperature heat energy, and then transfer it to the location requiring heating or cooling. They are highly favored by consumers and users, and are widely used for cooling and hot water supply in hotels, schools, hospitals, saunas, beauty salons, swimming pools, laundries, and other places.

[0003] The compressor is a core component of a heat pump system. At high frequencies, the electronic expansion valve opens wider, increasing the refrigerant mass flow rate. At low frequencies, the electronic expansion valve opens narrower, reducing the refrigerant mass flow rate. As heat pump systems expand in a wider range of applications and ambient temperatures, their frequency fluctuates significantly. In these situations, the compressor switches between high and low frequencies, and during this frequency switching, existing methods for adjusting the opening of the electronic expansion valve present challenges.

[0004] For example, the existing method of adjusting the opening of the electronic expansion valve according to the return air superheat or exhaust gas superheat takes a certain amount of time for the system to react due to the rapid change of the compressor frequency. During this process, it is easy to cause compressor liquid hammer and other protection problems.

[0005] For example, there is an existing method of linearly adjusting the opening of the electronic expansion valve based on the change of the compressor frequency, such as the method disclosed in Chinese Patent No. CN106568243A, which adjusts the opening of the electronic expansion valve based on the change of the compressor operating frequency, so that △P = (F2-F1)*a, where △P is the number of opening adjustment steps of the electronic expansion valve, F2 is the operating frequency of the compressor after the change, F1 is the operating frequency of the compressor before the change, and a is a preset coefficient; this adjustment method does not take into account that under low and high ambient temperatures, the opening of the electronic expansion valve and the compressor frequency are not in a single linear relationship, and cannot accurately control the opening of the electronic expansion valve to match the compressor frequency, resulting in a series of problems in the system under low or high ambient temperatures, which may lead to increased superheat, decreased evaporation performance, decreased system stability, compressor damage, etc. due to the mismatch between the frequency and the opening. Summary of the Invention

[0006] Based on this, the purpose of the present invention is to provide an electronic expansion valve control method based on frequency change rate to solve the problem of mismatch between the opening of the electronic expansion valve and the frequency of the compressor in the heat pump system under low ambient temperature and high ambient temperature conditions.

[0007] A method for controlling an electronic expansion valve based on a frequency change rate comprises the following steps:

[0008] Get the current operating frequency F of the compressor t , target operating frequency F target , and the current opening degree P of the electronic expansion valve t , calculate the compressor frequency change rate and the proposed target opening degree P of the electronic expansion valve 0 ;

[0009] According to the target opening degree P of the electronic expansion valve 0 , the opening correction coefficient β is determined by the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, and the opening correction coefficient β and the current operating frequency F are used. t , target operating frequency F target Calculate the target opening degree P of the electronic expansion valve target ;

[0010] Control the electronic expansion valve to adjust to the target opening P of the electronic expansion valve at a valve adjustment rate target .

[0011] Compared with the prior art, the present invention corrects the frequency change value through the correction coefficient of the frequency and the electronic expansion valve and then calculates the frequency change rate, and uses the characteristic relationship curve of the refrigerant mass flow-electronic expansion valve opening to calculate the slope, and corrects the electronic expansion valve opening through the slope and the frequency change rate to obtain the target opening of the electronic expansion valve corresponding to the compressor frequency reduction or increase. This control method overcomes the problem of inaccurate matching between frequency and opening caused by the calculation and control of the target opening of the electronic expansion valve according to the frequency change of the compressor in the prior art, eliminates the influence of low ambient temperature and high ambient temperature on the refrigerant mass flow, and enables the heat pump system to make more reasonable adjustments to the electronic expansion valve according to the current electronic expansion valve opening under low ambient temperature and high ambient temperature conditions, thereby improving the matching between frequency and opening, and avoiding compressor liquid hammer and other protection problems caused by mismatch of the electronic expansion valve opening due to frequency change.

[0012] Furthermore, the target opening degree P of the electronic expansion valve is 0 satisfy:

[0013] P 0 =P t +θ*(F target -F t )

[0014] Among them, Pt Indicates the current opening of the electronic expansion valve, F target Indicates the target operating frequency of the compressor, F t It represents the current operating frequency of the compressor, and θ represents the preset coefficient.

[0015] Furthermore, the target opening degree P of the electronic expansion valve target satisfy:

[0016]

[0017] Among them, β represents the target opening P 0 Determine the opening correction coefficient, α represents the correction coefficient of frequency and electronic expansion valve model, P t Indicates the current opening of the electronic expansion valve, F target Indicates the target operating frequency of the compressor, F t Indicates the current operating frequency of the compressor.

[0018] Furthermore, the opening correction coefficient β is determined as follows:

[0019] SA1 obtains the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, and sets the target opening P of the electronic expansion valve. 0 Determine the corresponding refrigerant mass flow rate f mass (P 0 );

[0020] SA2 uses numerical differentiation method to calculate the target opening P 0 The slope K of the opening correction coefficient β satisfies:

[0021] β=γ·K

[0022] Where γ is the slope correction factor and K represents the slope.

[0023] At the same time, the present invention also provides a heat pump system with electronic expansion valve control based on frequency change rate.

[0024] A heat pump system with electronic expansion valve control based on frequency change rate includes a compressor, a four-way valve, a water-side heat exchanger, an electronic expansion valve, an air-side heat exchanger connected in sequence through a refrigerant circulation pipeline, and a controller communicatively connected to the compressor and the electronic expansion valve. The controller executes any of the above-mentioned electronic expansion valve control methods based on frequency change rate to control the opening of the electronic expansion valve.

[0025] The beneficial effects of the heat pump system proposed in the present invention are the same as those of the above-mentioned electronic expansion valve control method based on the frequency change rate, and will not be described in detail here.

[0026] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the system structure of an embodiment of the present invention;

[0028] Figure 2 This is a flow chart of an electronic expansion valve control method according to an embodiment of the present invention;

[0029] Figure 3 This is a refrigerant mass flow-opening characteristic curve of an electronic expansion valve. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiments of the present invention.

[0031] In order to solve the problem that the existing method of linearly adjusting the opening of the electronic expansion valve according to the change of the compressor frequency through a correction coefficient does not take into account that under low ambient temperature and high ambient temperature conditions, the opening of the electronic expansion valve and the compressor frequency are not in a single linear relationship, which results in the inability to accurately control the opening of the electronic expansion valve to adjust the refrigerant flow to match the compressor frequency under low ambient temperature or high ambient temperature, causing the system to have a series of problems under low ambient temperature or high ambient temperature conditions, such as increased superheat, decreased evaporation performance, decreased system stability, and compressor damage due to the mismatch between frequency and opening. The present invention proposes an electronic expansion valve control method based on the frequency change rate. The control method uses the frequency and the electronic expansion valve to adjust the opening of the electronic expansion valve according to the change of the compressor frequency. The correction coefficient of the valve is used to correct the frequency change value and then calculate the frequency change rate, and the slope is calculated using the characteristic relationship curve of the refrigerant mass flow rate-electronic expansion valve opening. The electronic expansion valve opening is corrected by the slope and the frequency change rate to obtain the target opening of the electronic expansion valve corresponding to the compressor frequency reduction or increase. This control method overcomes the problem of inaccurate matching between frequency and opening caused by the calculation and control of the target opening of the electronic expansion valve according to the frequency change of the compressor in the prior art, eliminates the influence of low ambient temperature and high ambient temperature on the refrigerant mass flow rate, and enables the heat pump system to make more reasonable adjustments to the electronic expansion valve according to the current electronic expansion valve opening when dealing with low ambient temperature and high ambient temperature conditions.

[0032] For specific implementation, please refer to Figure 1 The heat pump system with frequency-rate-based electronic expansion valve control proposed in the present invention includes a compressor 10, a four-way valve 20, a water-side heat exchanger 30, an electronic expansion valve 40, an air-side heat exchanger 50, a controller (not shown), and other auxiliary components, all connected in a refrigerant pipeline. The controller is in communication with the compressor 10 and the electronic expansion valve 40.

[0033] The electromagnetic expansion valve 40 is provided on the refrigerant pipeline between the water-side heat exchanger 30 and the air-side heat exchanger 50 to throttle the medium-temperature and high-pressure liquid refrigerant to a low-temperature and low-pressure refrigerant. Furthermore, the electromagnetic expansion valve 40 is also provided with a filter.

[0034] The controller includes a storage unit and a processing unit. The storage unit is used to receive the operating frequency of the compressor 10, the current opening of the electronic expansion valve 40 and its refrigerant mass flow-opening characteristic curve; the processing unit is used to calculate and control based on information such as the operating frequency, current opening and refrigerant mass flow-opening characteristic curve.

[0035] For details, please refer to Figure 2 The controller of the heat pump system of the present invention controls the electronic expansion valve through the following method.

[0036] S10 obtains the current operating frequency F of the compressor t , target operating frequency F target , and the current opening degree P of the electronic expansion valve t , calculate the proposed target opening P of the electronic expansion valve 0 .

[0037] Specifically, the target opening degree P of the electronic expansion valve is 0 satisfy:

[0038] P 0 =P t +θ*(F target -F t )

[0039] Among them, P t Indicates the current opening of the electronic expansion valve, F target Indicates the target operating frequency of the compressor, F t represents the current operating frequency of the compressor, θ represents a preset coefficient, and its value is selected according to the capacity of the compressor and the model of the electronic expansion valve. For example, the value range of θ can be 0.5-3. Preferably, the value of θ is 1.

[0040] S20 sets the target opening of the electronic expansion valve according to P 0 , the opening correction coefficient β is determined by the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, and the opening correction coefficient β and the current operating frequency F are used. t , target operating frequency F target Calculate the target opening degree P of the electronic expansion valve target .

[0041] Specifically, the target opening degree P of the electronic expansion valve target satisfy:

[0042]

[0043] Among them, β represents the target opening P 0 Determine the opening correction coefficient, α represents the correction coefficient of frequency and electronic expansion valve model, α ranges from 0.5 to 3, P t Indicates the current opening of the electronic expansion valve, F target Indicates the target operating frequency of the compressor, F t Indicates the current operating frequency of the compressor.

[0044] The determination method of β is as follows:

[0045] SA1 obtains the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, and sets the target opening P of the electronic expansion valve. 0 Determine the corresponding refrigerant mass flow rate f mass (P 0 );

[0046] SA2 uses numerical differentiation method to calculate the target opening P 0 The slope K of the opening correction coefficient β satisfies:

[0047] β=γ·K

[0048] Where γ is the slope correction factor and K is the slope. Figure 3 An example of a refrigerant mass flow rate-opening characteristic curve for an electronic expansion valve is provided. In the figure, for an electronic expansion valve opening of 0-300p, the K value is 9.5 / 300; for an electronic expansion valve opening of 301-500p, the K value is 11.8 / 500. The slope K varies depending on the electronic expansion valve used in the heat pump system, and the example provided in this application does not limit the slope K.

[0049] In specific implementation, forward difference method, backward difference method and central difference method can be used to solve the proposed target opening P 0 The slope K.

[0050] Use the forward difference method to solve the slope K: According to the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, determine the proposed target opening P 0 Forward opening P 0 +ΔP corresponding refrigerant mass flow rate f mass (P 0 +ΔP), then K satisfies:

[0051] K=(f mass (P 0 +ΔP)-f mass (P 0 )) / ΔP.

[0052] Use the backward difference method to solve the slope K: According to the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, determine the proposed target opening P 0 Backward opening P 0 -ΔP corresponding refrigerant mass flow rate f mass (P 0 -ΔP), then K satisfies:

[0053] K=(f mass (P 0 )-f mass (P 0 -ΔP)) / ΔP.

[0054] Use the central difference method to solve the slope K: According to the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, determine the proposed target opening P 0 Forward opening P 0 +ΔP corresponding refrigerant mass flow rate f mass (P 0 +ΔP), backward opening P 0 -ΔP corresponding refrigerant mass flow rate f mass (P 0 -ΔP), then K satisfies:

[0055] K=(f mass (P 0 +ΔP)-f mass (P 0 -ΔP)) / 2ΔP.

[0056] In the above method, ΔP is the minimum opening value, which is 1 to 3 pulses.

[0057] S30 controls the electronic expansion valve to adjust to the target opening degree P of the electronic expansion valve at a valve adjustment rate. target .

[0058] The following is an example of the electronic expansion valve adjustment corresponding to the frequency reduction using this method under low ambient temperature and high ambient temperature conditions, where the refrigerant mass flow-opening characteristic curve of the electronic expansion valve is as follows: Figure 3 As shown:

[0059] When operating at low ambient temperature, the required refrigerant mass flow rate is smaller: when the machine operating frequency is stable at 90Hz, the electronic expansion valve opening is 90p; when the machine frequency reduction is triggered, the frequency is reduced from 90Hz to the target frequency of 30Hz, and θ is 1, then the proposed target opening is 30p, and the corresponding slope in the characteristic curve is K = 9.5 / 300, γ = 300 / 9.5, then the opening correction coefficient β = 1, α = 0.5, corresponding to the target frequency of 30Hz, the electronic expansion valve should be adjusted to 1*90*|90-0.5*(90-30)| / 90 = 60 steps; when the compressor frequency is unloaded from 90Hz to 30Hz, the current electronic expansion valve opening is 60p.

[0060] During high ambient temperature operation, a larger refrigerant mass flow rate is required: when the machine operating frequency is stable at 90Hz, the electronic expansion valve opening is 360p; when the machine frequency reduction is triggered, the frequency is reduced from 90Hz to the target frequency of 30Hz, and θ is 1, then the proposed target opening is 300p. The corresponding slope in the characteristic curve is K = 11.8 / 500, γ = 300 / 9.5, then the opening correction coefficient β = 0.75 (retain two decimal places), α = 0.5, corresponding to the target frequency of 30Hz, the electronic expansion valve is adjusted to P2 = 0.75*360p*|90-0.5*(90-30)| / 90 = 180p; when the compressor frequency is unloaded from 90Hz to 30Hz, the current electronic expansion valve opening is 180p.

[0061] The present application corrects the frequency change value through the correction coefficient of the frequency and the electronic expansion valve and then calculates the frequency change rate, and uses the characteristic relationship curve of the refrigerant mass flow-electronic expansion valve opening to calculate the slope, and corrects the electronic expansion valve opening through the slope and frequency change rate to obtain the electronic expansion valve target opening corresponding to the compressor frequency reduction or increase. This control method overcomes the problem of inaccurate frequency and opening matching caused by the calculation and control of the electronic expansion valve target opening according to the compressor frequency change in the prior art, eliminates the influence of low ambient temperature and high ambient temperature on the refrigerant mass flow, and enables the heat pump system to cope with low ambient temperature and high ambient temperature conditions. The electronic expansion valve can make more reasonable adjustments according to the current electronic expansion valve opening, improve the frequency and opening matching, and avoid compressor liquid shock and other protection problems caused by the mismatch of the electronic expansion valve opening due to frequency changes.

[0062] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application. The singular forms of "a", "said" and "the" used in the embodiments of the present application and the claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that, unless otherwise specified, "multiple" and "several" refer to two or more; "and / or" refers to and includes any or all possible combinations of one or more associated listed items; "first", "second", "third" and the like are only used to distinguish, and are not used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. When the above description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of the present application, for those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0063] The above-described embodiments merely represent several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, and the present invention is intended to encompass such modifications and variations.

Claims

1. A method for controlling an electronic expansion valve based on a frequency change rate, characterized in that: include: Get the current operating frequency F of the compressor t , target operating frequency F target , and the current opening degree P of the electronic expansion valve t , calculate the proposed target opening P of the electronic expansion valve 0 ; According to the target opening degree P of the electronic expansion valve 0 , the opening correction coefficient β is determined by the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, and the opening correction coefficient β and the current operating frequency F are used. t , target operating frequency F target Calculate the target opening degree P of the electronic expansion valve target , where the target opening of the electronic expansion valve P target satisfy: Where, β represents the target opening P 0 Determine the opening correction coefficient, α represents the correction coefficient of frequency and electronic expansion valve model, P t Indicates the current opening of the electronic expansion valve, F target Indicates the target operating frequency of the compressor, F t Indicates the current operating frequency of the compressor; the opening correction coefficient β is determined as follows: SA1: Get the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, and set the target opening P of the electronic expansion valve. 0 Determine the corresponding refrigerant mass flow rate f mass (P 0 ); SA2: Use numerical differentiation method to find the target opening P 0 The slope K of the opening correction coefficient β satisfies: β=γ·K Where γ is the slope correction factor and K represents the slope; Control the electronic expansion valve to adjust to the target opening P of the electronic expansion valve at a valve adjustment rate target .

2. The electronic expansion valve control method according to claim 1, characterized in that: The target opening degree P of the electronic expansion valve is 0 satisfy: P 0 =P t +θ*(F target -F t ) Among them, P t Indicates the current opening of the electronic expansion valve, F target Indicates the target operating frequency of the compressor, F t It represents the current operating frequency of the compressor, and θ represents the preset coefficient.

3. The electronic expansion valve control method according to claim 1, characterized in that: The slope K is calculated as follows: According to the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, determine the target opening P 0 Forward opening P 0 +ΔP corresponding refrigerant mass flow rate f mass (P 0 +ΔP), then K satisfies: K=(f mass (P 0 +ΔP)-f mass (P 0 )) / ΔP; ΔP is the minimum opening value, ranging from 1 to 3 pulses.

4. The electronic expansion valve control method according to claim 1, characterized in that: The slope K is calculated as follows: According to the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, determine the target opening P 0 Backward opening P 0 -ΔP corresponding refrigerant mass flow rate f mass (P 0 -ΔP), then K satisfies: K=(f mass (P 0 )-f mass (P 0 -ΔP)) / ΔP; ΔP is the minimum opening value, ranging from 1 to 3 pulses.

5. The electronic expansion valve control method according to claim 1, characterized in that: The slope K is calculated as follows: According to the refrigerant mass flow-opening characteristic curve of the electronic expansion valve, determine the target opening P 0 Forward opening P 0 +ΔP corresponding refrigerant mass flow rate f mass (P 0 +ΔP), backward opening P 0 -ΔP corresponding refrigerant mass flow rate f mass (P 0 -ΔP), then K satisfies: K=(f mass (P 0 +ΔP)-f mass (P 0 -ΔP)) / 2ΔP; ΔP is the minimum opening value, ranging from 1 to 3 pulses.

6. The electronic expansion valve control method according to any one of claims 1 to 5, characterized in that: The correction coefficient α of the frequency and the electronic expansion valve model ranges from 0.5 to 3.

7. A heat pump system with an electronic expansion valve control based on a frequency change rate, comprising a compressor, a four-way valve, a water-side heat exchanger, an electronic expansion valve, an air-side heat exchanger sequentially connected via a refrigerant circulation pipeline, and a controller communicatively connected to the compressor and the electronic expansion valve, characterized in that: The controller executes the electronic expansion valve control method based on the frequency change rate according to any one of claims 1 to 6 to control the opening of the electronic expansion valve.

8. The heat pump system according to claim 7, characterized in that The electronic expansion valve is also connected to a filter.

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