Electronic expansion valve control method

Abstract

This invention provides an electronic expansion valve control method. The superheat is calculated using intake temperature and intake pressure. Based on the calculated superheat and a setpoint, a PID algorithm is used to obtain the rapid response value of the electronic expansion valve. This application establishes an allowable error range. That is, when the detected data is within the allowable error range, the PID algorithm will not achieve rapid adjustment of the electronic expansion valve. Furthermore, when the superheat is within the error range, data from multiple time periods needs to be collected and the trend of data change over time analyzed. The opening of the expansion valve is controlled based on the trend change. This eliminates the need for multiple PID algorithms to control the expansion valve opening, reducing the number of control parameters. Simultaneously, even when the difference between the detected superheat value and the setpoint is small, the opening of the electronic expansion valve can still be controlled by analyzing the superheat trend, achieving precise control.

Description

Technical Field

[0001] This invention belongs to the field of expansion valve control technology, specifically relating to an electronic expansion valve control method. Background Technology

[0002] In refrigeration systems, electronic expansion valves offer advantages such as energy saving, low operating temperature, high accuracy, and fast response, enabling the most comfortable and energy-efficient control of the air conditioning system. Therefore, electronic expansion valves are widely used in air conditioning units, especially in inverter air conditioning units.

[0003] Currently, the control method for electronic expansion valves typically employs multi-segment PID algorithms, which achieves fast adjustment response and rapid stabilization after external disturbances. However, this method involves numerous parameters, making parameter tuning complex. Summary of the Invention

[0004] This invention provides an electronic expansion valve control method, which aims to solve the problem that there are many parameters and the parameter tuning is complicated in the existing electronic expansion valve control methods.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: to provide an electronic expansion valve control method, comprising:

[0006] Step S1: Calculate the superheat and, based on the superheat and the set value, obtain the fast response value of the electronic expansion valve through a PID algorithm;

[0007] Step S2: Define the difference range between the superheat setpoint and the setpoint as ±K. The difference in superheat within ±K is defined as the allowable error range.

[0008] Step S3: When the superheat is within the error range, control the opening of the electronic expansion valve according to the analyzed superheat trend;

[0009] Step S4: Perform PID algorithm adjustment outside the error region, and do not perform PID algorithm adjustment within the error region.

[0010] In one possible implementation, in step S3, when the superheat is increasing, the opening of the electronic expansion valve is increased; when the superheat is decreasing, the opening of the electronic expansion valve is decreased; and when the superheat is in a steady state, the opening of the electronic expansion valve is maintained.

[0011] In one possible implementation, step S3 further includes:

[0012] Define the superheat data acquisition interval and define the output of an analysis result after sampling n samples;

[0013] The MK algorithm is used to calculate the test statistic S based on n sampled data.

[0014] Based on the obtained test statistic S, the standardized test statistic Z is derived, and the trend of the n samples is determined based on the value of Z.

[0015] In one possible implementation, step S3 further includes:

[0016] Define a confidence level α, and determine whether the upward and downward trends meet the significance test of the confidence level based on the absolute value of Z, in order to determine whether the opening of the control valve should be controlled according to the trend.

[0017] In one possible implementation, in step S3, when the current superheat is less than a set value:

[0018] When the trend is determined to be upward, the opening of the electronic expansion valve is kept constant.

[0019] When the trend is determined to be steady state, the opening of the electronic expansion valve is reduced by a certain value.

[0020] When the trend is determined to be downward, the opening of the electronic expansion valve is reduced by a certain amount.

[0021] In one possible implementation, in step S3, when the current superheat is greater than a set value:

[0022] If the trend is determined to be upward, the opening of the electronic expansion valve is increased by a certain value.

[0023] When the trend is determined to be steady state, the opening of the electronic expansion valve is increased by a certain value.

[0024] If the trend is determined to be downward, the opening of the electronic expansion valve should remain unchanged.

[0025] In one possible implementation, after the trend determination is completed, the opening of the electronic expansion valve is adjusted over a period of time after n sampling acquisitions are completed.

[0026] In one possible implementation, the opening degree of the electronic expansion valve is adjusted manually, and the magnitude of the change is adjustable.

[0027] The solution presented in this application, compared to existing technologies, calculates superheat based on intake temperature and pressure, and then uses a PID algorithm to obtain the rapid response value of the electronic expansion valve based on the calculated superheat and a set value. This application, however, sets an allowable error range. That is, when the detected data is within the allowable error range, the PID algorithm will not be used to quickly adjust the electronic expansion valve. Furthermore, when the superheat is within the error range, data from multiple time periods needs to be collected and the trend of data changes over time analyzed to control the opening of the expansion valve based on the trend. This eliminates the need for multiple PID algorithms to control the expansion valve opening, reducing the number of control parameters. Simultaneously, even when the difference between the detected superheat value and the set value is small, the opening of the electronic expansion valve can still be controlled by analyzing the trend of superheat, achieving precise control. Attached Figure Description

[0028] Figure 1 Flowchart of the electronic expansion valve control method provided in the embodiments of the present invention Figure 1 ;

[0029] Figure 2 Flowchart of the electronic expansion valve control method provided in the embodiments of the present invention Figure 2 . Detailed Implementation

[0030] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] Please refer to the following: Figure 1 and Figure 2 The electronic expansion valve control method provided by the present invention will now be described. The electronic expansion valve control method includes:

[0032] Step S1: Calculate the superheat and, based on the superheat and the set value, obtain the fast response value of the electronic expansion valve through a PID algorithm;

[0033] Step S2: Define the difference range between the superheat setpoint and the setpoint as ±K. The difference in superheat within ±K is defined as the allowable error range.

[0034] Step S3: When the superheat is within the error range, control the opening of the electronic expansion valve according to the analyzed superheat trend;

[0035] Step S4: Perform PID algorithm adjustment outside the error region, and do not perform PID algorithm adjustment within the error region.

[0036] The electronic expansion valve control method provided in this embodiment, compared with the prior art, calculates the superheat based on the intake temperature and intake pressure, and obtains the rapid response value of the electronic expansion valve through a PID algorithm based on the calculated superheat and the set value. This application sets an allowable error range. That is, when the detected data is within the allowable error range, the PID algorithm will not achieve rapid adjustment of the electronic expansion valve. Furthermore, when the superheat is within the error range, data from multiple time periods needs to be collected and the trend of data change over time needs to be analyzed to control the opening of the expansion valve based on the trend. On the one hand, this eliminates the need for multiple PID algorithms to control the expansion valve opening, reducing the number of control parameters. On the other hand, even when the difference between the detected superheat value and the set value is small, the opening of the electronic expansion valve can still be controlled by analyzing the trend of superheat, achieving a precise control effect.

[0037] Specifically, in this embodiment, K is set to 1. When the difference between the superheat detection value and the set value is within ±1, the opening degree of the electronic expansion valve is controlled by analyzing the trend of the difference between the detection value and the set value over multiple consecutive time periods.

[0038] In one embodiment, step S3 described above can be performed as follows: Figure 1 The structure shown. See also Figure 1 In step S3, when the superheat is increasing, the opening of the electronic expansion valve is increased; when the superheat is decreasing, the opening of the electronic expansion valve is decreased; and when the superheat is in a steady state, the opening of the electronic expansion valve is maintained. When the difference between the detected superheat and the set value is within ±K, and the detected superheat is increasing over time, the opening of the electronic expansion valve is increased to enhance the cooling and heat exchange effect. Conversely, when the detected difference is decreasing during the detection period, the opening of the electronic expansion valve is decreased to reduce the cooling and heat exchange effect. This allows for adjustment of the electronic expansion valve within a small range, improving the control accuracy of the refrigeration system.

[0039] In some embodiments, step S3 above can be adopted as follows: Figure 1 The structure shown. See also Figure 1 Step S3 also includes:

[0040] Define the superheat data acquisition interval and define the output of an analysis result after sampling n samples;

[0041] The MK algorithm is used to calculate the test statistic S based on n sampled data.

[0042] Based on the obtained test statistic S, the standardized test statistic Z is derived, and the trend of the n samples is determined based on the value of Z.

[0043] The value of n is defined as 10, and data is collected sequentially at 500-millisecond intervals. The MK algorithm is used to analyze the n samples, and the test statistic S is calculated using a formula. A standardized test statistic Z is then derived from the test statistic, and the value of Z is used to determine the trend of change among the n samples. However, when values ​​exhibit irregular changes within the same collection period, or when affected by external interference, arbitrarily selecting two values ​​will not directly represent the trend of overheating within that time period.

[0044] This application obtains the standardized test statistic Z using the following calculation formula. The standardized test statistic Z is used to determine the trend of overheating within the time period of n, which is more accurate and precise.

[0045] The sampling period is set to 500 milliseconds. Analysis results are output every 10 samples, and the test statistic S is calculated. In the MK test, the null hypothesis H0 (no monotonic trend) is that the time series data (X_{1}, X_{2}, ... X_{n}) are n independent, identically distributed random variables. The alternative hypothesis H1 (existence of monotonic trend) is a two-sided test. For all i,j≤n and i≠j, the distributions of X_{i} and X_{j} are different, where n=10, and X_{i} and X_{j} are the observations corresponding to the i-th and j-th time series, respectively. <j。

[0046]

[0047]

[0048]

[0049] When n≥8, the statistic S roughly follows a normal distribution. Without considering the existence of equal data points in the sequence, its mean E(S)=0 and the simplified formula for variance is Var(S)=n(n-1)(2n+5) / 18.

[0050] A positive value for the standardized test statistic Z indicates an increasing trend in overheating during the sampling period. A negative value for Z indicates a decreasing trend in overheating during the sampling period.

[0051] In some embodiments, step S3 above can be adopted as follows: Figure 1 The structure shown. See also Figure 1Step S3 further includes defining a confidence level α and determining whether the upward or downward trend meets the significance test based on the absolute value of Z, thus deciding whether to control the valve opening based on the trend. Given a confidence level (significance level) α, if |Z| ≥ Z(1-α / 2), then the null hypothesis H0 is unacceptable, meaning that at the confidence level α (significance test level), the time series data exhibits a clear upward or downward trend. A positive Z value indicates an upward trend, and a negative Z value indicates a decreasing trend. Absolute values ​​of Z greater than or equal to 1.645, 1.96, and 2.576 indicate that the significance test has passed at 90%, 95%, and 99% confidence levels, respectively. Calculation process: α=0.1, Z(1-α / 2)=0.95, looking up the standard normal distribution table, Z0.95=1.645, so when |Z|≥1.645, it passes the 90% significance test, the H0 hypothesis is not true, Z>0, the sequence has an upward trend, Z<0, the sequence has a downward trend, otherwise the H0 hypothesis is true, and it is defined as steady state.

[0052] Specifically, in this embodiment, the confidence level α is set to 0.1.

[0053] By analyzing the confidence level, we can verify the accuracy of trend analysis within the sampling period, which can effectively improve the accuracy of trend analysis and enable more precise control of the opening of the electronic expansion valve.

[0054] In some embodiments, the determination method in step S3 above can be as follows: Figure 1 The structure shown. See also Figure 1 In step S3, when the current superheat is less than the set value: if the trend is determined to be upward, the opening of the electronic expansion valve is kept constant; if the trend is determined to be steady, the opening of the electronic expansion valve is reduced by a certain value; if the trend is determined to be downward, the opening of the electronic expansion valve is reduced by a certain value. First, the detected superheat value is compared with the set value. When the superheat is less than the set value, the opening of the electronic expansion valve is controlled according to the different trend changes, so that the superheat gradually approaches the set value.

[0055] Specifically, in this embodiment, in step S3, when the current superheat is greater than the set value: if the trend is determined to be an upward trend, the opening of the electronic expansion valve is increased by a certain value; if the trend is determined to be a steady state, the opening of the electronic expansion valve is increased by a certain value; if the trend is determined to be a downward trend, the opening of the electronic expansion valve remains unchanged.

[0056] In some embodiments, after the execution time for controlling the opening of the electronic expansion valve is completed based on trend determination, the opening of the electronic expansion valve is adjusted after n sampling acquisitions. Superheat is collected during the sampling cycle, and the collected data is saved. After n data points are collected, the data is analyzed, and the trend is determined. The adjustment of the electronic expansion valve opening is determined based on the trend and a comparison between the current superheat and the set value. Adjusting the electronic expansion valve opening only after the sampling cycle ends avoids interference with subsequent data.

[0057] Preferably, in this embodiment, the opening degree of the electronic expansion valve is adjusted manually, and the magnitude of the change is adjustable. The adjustment value of the electronic expansion valve opening can be set and adjusted manually. The opening degree adjustment of the electronic expansion valve can be set according to the refrigeration system, achieving more precise and accurate control.

[0058] Preferably, in this embodiment, the opening degree of the electronic expansion valve is increased by 0.2% in a single adjustment.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling an electronic expansion valve, characterized in that, include: Step S1: Calculate the superheat and, based on the superheat and the set value, obtain the fast response value of the electronic expansion valve through a PID algorithm; Step S2: Define the difference range between the superheat setpoint and the setpoint as ±K. The difference in superheat within ±K is defined as the allowable error range. Step S3: When the superheat is within the error range, control the opening of the electronic expansion valve according to the analyzed superheat trend; Step S4: Perform PID algorithm adjustment outside the error region, and do not perform PID algorithm adjustment within the error region; Step S3 also includes: Define the superheat data acquisition interval and define the output of an analysis result after sampling n samples; The MK algorithm is used to calculate the test statistic S based on n sampled data. Based on the obtained test statistic S, the standardized test statistic Z is derived, and the trend of the n samples is determined based on the value of Z.

2. The electronic expansion valve control method as described in claim 1, characterized in that, In step S3, when the superheat is increasing, the opening of the electronic expansion valve is increased; when the superheat is decreasing, the opening of the electronic expansion valve is decreased; and when the superheat is in a steady state, the opening of the electronic expansion valve is maintained.

3. The electronic expansion valve control method as described in claim 1, characterized in that, Step S3 also includes: Define a confidence level α, and determine whether the upward and downward trends meet the significance test of the confidence level based on the absolute value of Z, in order to determine whether the opening of the control valve should be controlled according to the trend.

4. The electronic expansion valve control method as described in claim 3, characterized in that, In step S3, when the current superheat is less than the set value: When the trend is determined to be upward, the opening of the electronic expansion valve is kept constant. When the trend is determined to be steady state, the opening of the electronic expansion valve is reduced by a certain value. When the trend is determined to be downward, the opening of the electronic expansion valve is reduced by a certain amount.

5. The electronic expansion valve control method as described in claim 3, characterized in that, In step S3, when the current superheat is greater than the set value: If the trend is determined to be upward, the opening of the electronic expansion valve is increased by a certain value. When the trend is determined to be steady state, the opening of the electronic expansion valve is increased by a certain value. If the trend is determined to be downward, the opening of the electronic expansion valve should remain unchanged.

6. The electronic expansion valve control method as described in claim 4 or 5, characterized in that, After the trend determination is completed, the opening degree of the electronic expansion valve is adjusted after n sampling acquisitions are completed.

7. The electronic expansion valve control method as described in claim 1, characterized in that, The opening degree of the electronic expansion valve can be adjusted manually, and the magnitude of the change is adjustable.

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