An adaptive energy-saving refrigeration constant temperature control method and system

Abstract

The present invention discloses an adaptive energy-saving refrigeration constant temperature control method and system, including: starting the refrigeration system, first comparing the compressor exhaust temperature with the ambient temperature, controlling the main valve opening accordingly, monitoring the real-time temperature of the controlled equipment based on a preset PID program, adjusting the auxiliary valve opening after comparing with the preset target temperature, and after completing the auxiliary valve control, implementing the auxiliary valve adaptive energy-saving control in combination with the real-time temperature and the compressor operating frequency, starting the self-tuning mode: allowing the compressor, the main valve, and the auxiliary valve to operate in a preset mode, calculating the mean square error of the real-time temperature within a preset cycle, and if the error is less than a preset threshold, updating the PID parameters to perform the next cycle constant temperature control; otherwise, maintaining the original PID program for constant temperature control. The present invention realizes a rapid response after the refrigeration system is started, and the parameter self-tuning control logic can obtain better control parameters to achieve higher-precision control.

Description

Technical Field

[0001] The present invention belongs to the technical field of constant temperature control, and in particular relates to an adaptive energy-saving refrigeration constant temperature control method and system. Background Art

[0002] Temperature control technology is increasingly being used in various fields, such as boiler heating in the industrial field, precise temperature control of CNC lathes, constant temperature storage of vaccines and drugs, constant temperature storage of food in refrigerators and cold storage, etc. However, most of the widely used temperature control technologies are still based on the research of fixed-frequency equipment. The most typical and widely used is the control method of target temperature plus differential temperature. Although this control method has the advantages of simple implementation plan and low cost, its disadvantage of controlling temperature fluctuations has increasingly reflected its shortcomings in modern industries and food industries with increasing requirements for temperature control.

[0003] With the rapid development of the economy, especially the improvement of people's requirements for life experience, the requirements for temperature control are also getting higher and higher, such as the comfort of the air-conditioned environment, the preservation and transportation of fruits, vegetables and flowers, and even the refrigerated storage of some precious drugs in the medical field. The constant temperature accuracy reaches ±0.1℃, or even ±0.01℃. Such high constant temperature requirements are far from being met by the traditional target temperature plus differential temperature control method. On the other hand, in today's increasingly tense energy environment, improving the energy efficiency of the constant temperature system is also a very important indicator. The traditional target temperature plus differential temperature and the constant temperature system using fixed frequency equipment is a very energy-consuming system and a rough system that is only suitable for the rough economic environment in the past. And the PID control of its system has the disadvantage of difficult PID parameter adjustment in different load application scenarios. Summary of the invention

[0004] The object of the present invention is to provide an adaptive energy-saving refrigeration constant temperature control method and system to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides an adaptive energy-saving refrigeration constant temperature control method, comprising:

[0006] Step 1: starting the refrigeration system, obtaining the exhaust temperature of the compressor and the ambient temperature in the refrigeration system, and controlling the opening of the main valve in the refrigeration system based on a comparison result between the exhaust temperature and the ambient temperature;

[0007] Step 2: After the main valve control is completed, the real-time temperature of the controlled equipment in the refrigeration system is obtained based on the preset PID program, and it is determined whether the real-time temperature reaches the preset target temperature, and the opening of the auxiliary valve in the refrigeration system is controlled based on the determination result;

[0008] Step 3: After the auxiliary valve control is completed, the auxiliary valve is adaptively controlled for energy saving based on the real-time temperature and the operating frequency of the compressor;

[0009] Step 4: After the adaptive energy-saving control is completed, start the self-tuning mode, which includes:

[0010] The compressor, the main valve and the auxiliary valve in the refrigeration system are operated in a preset mode, and the real-time temperature within a preset period is obtained, and the mean square error of the real-time temperature within the preset period is calculated. If the mean square error is less than a preset threshold, the parameters of the preset PID program are updated, and the constant temperature control of the refrigeration system for the next period is performed based on the PID program after the parameter update; if the mean square error is greater than the preset threshold, the self-tuning mode is terminated, and the constant temperature control of the refrigeration system for the next period is performed based on the original preset PID program.

[0011] Optionally, controlling the opening of a main valve in the refrigeration system specifically includes:

[0012] When the exhaust temperature is less than the sum of the ambient temperature and the preset exhaust temperature hysteresis value, reducing the opening of the main valve;

[0013] When the exhaust temperature is greater than the sum of the ambient temperature and the preset exhaust temperature hysteresis value, main valve superheat control is performed.

[0014] Optionally, the process of executing main valve superheat control specifically includes:

[0015] Calculate the difference between the outlet and inlet temperatures of the evaporator in the refrigeration system to obtain the superheat;

[0016] When the superheat is greater than the sum of a preset target superheat and a preset dead zone value, increasing the opening of the main valve;

[0017] When the superheat is less than the difference between the preset target superheat and the preset dead zone value, the opening of the main valve is reduced.

[0018] Optionally, the controlling the opening degree of the auxiliary valve in the refrigeration system specifically includes:

[0019] When the real-time temperature is greater than the sum of the preset target temperature and the preset dead zone value, reducing the opening of the auxiliary valve;

[0020] When the real-time temperature is less than the difference between the preset target temperature and the preset dead zone value, the opening of the auxiliary valve is increased.

[0021] Optionally, the adaptive energy-saving control of the auxiliary valve based on the real-time temperature and the operating frequency of the compressor specifically includes:

[0022] The mean square error value of the real-time temperature within a preset period is measured. When the mean square error value is less than the preset value, the operating frequency of the compressor is greater than the preset operating frequency and the auxiliary valve opening is greater than zero, the auxiliary valve opening is reduced according to the preset period and small steps.

[0023] Optionally, during the process of controlling the opening of the main valve and the auxiliary valve, the opening increment and adjustment time interval corresponding to each valve both change in accordance with the exponential law.

[0024] An adaptive energy-saving refrigeration constant temperature control system, used to implement the adaptive energy-saving refrigeration constant temperature control method, comprises a controller and a refrigeration system, the refrigeration system comprises a refrigeration circuit composed of a compressor, a condenser, a drying filter, a switch type solenoid valve, a main valve and an evaporator connected in series in sequence, the exhaust port of the compressor is connected to the inlet of the evaporator through the auxiliary valve;

[0025] The evaporator is installed in the controlled device, and the exhaust port of the compressor, the inlet and outlet of the evaporator and the controlled device are all equipped with temperature sensors;

[0026] The compressor, condenser, filter drier, on / off solenoid valve, main valve, auxiliary valve, evaporator and each of the temperature sensors are electrically connected to the controller.

[0027] Optionally, the controller integrates a microprocessor, a storage device, a digital-to-analog converter, an RS485 communication circuit, an electronic expansion valve drive circuit and a power supply circuit.

[0028] The technical effects of the present invention are:

[0029] The present invention realizes a rapid response after the refrigeration system is started; the one-button PID parameter self-tuning control logic of the present invention can obtain more optimal control parameters to achieve higher-precision control, and can effectively control the deviation between the temperature and the target temperature within ±0.1°C; the superheat control method of the main valve of the present invention makes the refrigerant heat exchange more sufficient to obtain a better refrigeration effect; the bypass-type regulation of the auxiliary valve of the present invention can effectively reduce the overshoot occurring in the temperature response process, and at the same time more effectively reduce energy consumption in the constant temperature process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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 work.

[0031] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0032] Figure 1 A flow chart of a system dynamic process control method in an embodiment of the present invention;

[0033] Figure 2 is a flow chart of a control method of a main valve in an embodiment of the present invention;

[0034] Figure 3 This is a flow chart for adjusting the opening degree of the auxiliary valve in the embodiment of the present invention when the auxiliary valve is used in a bypass mode;

[0035] Figure 4 This is a flow chart of energy saving achieved by adaptively adjusting the opening of the auxiliary valve in the embodiment of the present invention;

[0036] Figure 5 A one-button PID parameter self-tuning flow chart in an embodiment of the present invention;

[0037] Figure 6 is a graph showing the relationship between the opening increment and the temperature deviation of the electronic expansion valve in an embodiment of the present invention;

[0038] Figure 7 is a diagram showing the relationship between the electronic expansion valve adjustment period and the temperature deviation in an embodiment of the present invention;

[0039] Figure 8 A schematic diagram of the structure of a high-precision adaptive energy-saving refrigeration constant temperature control system in an embodiment of the present invention;

[0040] Explanation of reference numbers: 1. Controller; 2. Variable frequency compressor; 3. Main valve electronic expansion valve; 4. Auxiliary valve electronic expansion valve; 5. Exhaust temperature sensor; 6. Evaporator inlet temperature sensor; 7. Evaporator outlet (return air) temperature sensor; 8. Controlled object (storage temperature) temperature sensor; 9. Condenser; 10. Evaporator; 11. Dry filter; 12. Switching solenoid valve. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0044] The words “include,” “including,” “have,” “contain,” etc. used in this article are open-ended terms, meaning including but not limited to.

[0045] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0046] Embodiment 1

[0047] like Figure 1 - Figure 8 As shown, this embodiment provides an adaptive energy-saving refrigeration constant temperature control method, including:

[0048] Step 1: starting the refrigeration system, obtaining the exhaust temperature of the compressor and the ambient temperature in the refrigeration system, and controlling the opening of the main valve in the refrigeration system based on a comparison result between the exhaust temperature and the ambient temperature;

[0049] Step 2: After the main valve control is completed, the real-time temperature of the controlled equipment in the refrigeration system is obtained based on the preset PID program, and it is determined whether the real-time temperature reaches the preset target temperature, and the opening of the auxiliary valve in the refrigeration system is controlled based on the determination result;

[0050] Step 3: After the auxiliary valve control is completed, the auxiliary valve is adaptively controlled for energy saving based on the real-time temperature and the operating frequency of the compressor;

[0051] Step 4: After the adaptive energy-saving control is completed, start the self-tuning mode, which includes:

[0052] The compressor, the main valve and the auxiliary valve in the refrigeration system are operated in a preset mode, and the real-time temperature within a preset period is obtained, and the mean square error of the real-time temperature within the preset period is calculated. If the mean square error is less than a preset threshold, the parameters of the preset PID program are updated, and the constant temperature control of the refrigeration system for the next period is performed based on the PID program after the parameter update; if the mean square error is greater than the preset threshold, the self-tuning mode is terminated, and the constant temperature control of the refrigeration system for the next period is performed based on the original preset PID program.

[0053] An adaptive energy-saving refrigeration constant temperature control system, used to implement the adaptive energy-saving refrigeration constant temperature control method, includes a controller 1, a variable frequency compressor 2, a main valve electronic expansion valve 3, a secondary valve electronic expansion valve 4, an exhaust temperature sensor 5, an evaporator inlet temperature sensor 6, an evaporator outlet (return air) temperature sensor 7, a controlled object (storage temperature) temperature sensor 8, a condenser 9, an evaporator 10, a drying filter 11, and a switch type solenoid valve 12. The controller 1 is composed of a microprocessor, a storage, a digital-to-analog converter, an RS485 communication circuit, an electronic expansion valve drive circuit, and a power supply circuit; the controlled object is the temperature of a refrigerator or a cold storage.

[0054] The purpose of this embodiment is to propose a high-precision and high-energy-efficiency constant temperature control method and system for application in cold storage and freezers, aiming to improve the quality of these equipment. However, a more valuable application is for application scenarios that require a high-quality constant temperature environment, such as medicine warehouses, fruit and vegetable preservation, CNC precision processing, etc. The control method and system proposed in this embodiment will play a key role. The method proposed in this embodiment is a control scheme based on variable frequency combined with traditional PID algorithm. The more significant feature is the integration of the exponential trend opening adjustment of the throttling electronic expansion valve and the bypass electronic expansion valve, thereby avoiding the conflict of complex systems using multiple PID algorithms and obtaining a better constant temperature effect.

[0055] A high-precision and high-energy-efficiency refrigeration constant temperature control method mainly includes the following steps: 1-fast refrigeration startup process, 2-PID adjustment of the frequency of the frequency conversion device (hereinafter referred to as the frequency conversion compressor) to make the controlled temperature close to the target temperature, 3-throttling electronic expansion valve (hereinafter referred to as the main valve) to adjust the superheat of the evaporator, 4-bypass electronic expansion valve (hereinafter referred to as the auxiliary valve) to adjust the opening in accordance with the frequency change of the frequency conversion device to further reduce the system control error, 5-adaptive energy-saving adjustment, 6-exponential trend type nonlinear valve opening adjustment method.

[0056] 1. Rapid refrigeration startup process: A refrigeration process with rapid startup performance plays a key role in achieving rapid response of the system. This embodiment proposes an effective startup control logic for this characteristic. The implementation process is as follows. Target exhaust temperature T EsvIt is set according to the inherent characteristics of the refrigeration system and is often required to have a higher value, such as T Esv >75℃ and above, the system begins to have a good refrigeration capacity. Therefore, when the control logic system involved in this embodiment starts, it first determines the exhaust temperature T of the variable frequency compressor. Epv Whether the target exhaust temperature T is reached Esv If the target exhaust temperature is not reached, the main valve opening is adjusted to a smaller value to increase the refrigerant pressure and raise the exhaust temperature. Epv Greater than T Esv After that, the main valve exits the control mode of small opening adjustment and enters the superheat adjustment mode.

[0057] 2. PID regulation control, adjust the frequency of the variable frequency compressor according to the deviation between the measured temperature and the target temperature to obtain different cooling capacities and control the measured temperature to be close to the target temperature. PID regulation is also known as proportional, integral, and differential regulation. It is a classic and mature control method that has been widely used in many application scenarios such as speed, position, and temperature control. However, the constant temperature control method involved in this embodiment proposes a one-button self-tuning PID parameter control logic to solve the difficulty of adjusting PID parameters in the process of PID control.

[0058] 3. Main valve throttling adjustment. The main valve is mainly used to adjust the flow of refrigerant entering the evaporator to achieve superheat regulation. The control method involved in this embodiment uses the difference between the outlet temperature and the inlet temperature of the evaporator as the superheat of the refrigeration system. According to the inherent characteristics of the refrigeration system, the closer the superheat is to zero, the more fully the refrigerant is evaporated in the evaporator and the higher the refrigeration efficiency of the system. By adjusting the opening of the main valve to control the flow of refrigerant entering the evaporator, the evaporation degree of the refrigerant can be effectively controlled. Therefore, the control method involved in this embodiment controls the superheat by controlling the difference between the outlet and inlet temperatures of the evaporator, so that the temperature difference is close to zero.

[0059] 4. Auxiliary valve adjustment. The auxiliary valve in the constant temperature system involved in this embodiment is used as a bypass valve, that is, the refrigerant sprayed from the compressor is directly returned to the compressor without passing through the evaporator for heat exchange. The main function of this control method is to weaken the refrigeration effect and can effectively avoid temperature overshoot when the PID adjustment frequency is used for temperature control.

[0060] 5. Adaptive energy-saving adjustment. The main energy-consuming device of the constant temperature control system involved in this embodiment is the variable frequency compressor. The higher the operating frequency, the higher the energy consumption, and the lower the operating frequency, the lower the energy consumption. Therefore, the opening adjustment of the auxiliary valve in the control method proposed in this embodiment not only bypasses the cooling capacity to avoid overshoot of the temperature response process, but is also the key to adaptive energy saving. When the measured temperature has gone through a cooling process and approaches the target temperature and enters the dead zone, the system will determine whether the measured temperature has stabilized. If the measured temperature has stabilized, it will determine whether the compressor operating frequency is greater than the minimum operating frequency. If it is greater than the minimum operating frequency, it will determine whether the auxiliary valve opening is open. If the auxiliary valve opening is greater than zero at this time, it indicates that there is still some excess refrigerant being bypassed at the current operating frequency. The system will try to close the auxiliary valve opening with a longer cycle, such as 5 minutes, and a smaller step size, such as 1%, so as to increase the refrigerant entering the evaporator for heat exchange. The final effect is that the measured temperature will exceed the dead zone and be slightly lower than the target temperature. However, due to the automatic adjustment capability of PID, the output frequency of PID will be reduced at this time to compensate for the downward deviation of the measured temperature. Finally, the measured temperature will stabilize at a lower compressor operating frequency, thereby achieving energy-saving effects.

[0061] 6. Exponential trend nonlinear valve opening adjustment method. The adjustment of the main valve and the auxiliary valve in the thermostatic control system involved in this embodiment does not adopt the traditional linear adjustment or PID adjustment, but adopts the exponential cycle and exponential step adjustment method. The main valve is used to control the superheat of the system, and the opening is adjusted according to the set target superheat; the auxiliary valve is used to bypass the excess cooling capacity under the current target temperature, and adopts the exponential cycle and exponential step adjustment method like the main valve. This adjustment method is based on the measured value T pv With the target value T sv The difference is adjusted, that is, T pv With T sv The larger the deviation, the shorter the valve adjustment cycle and the larger the opening increment each time. pv With T sv The smaller the deviation, the longer the valve adjustment cycle, the smaller the opening each time, and the trend process is based on the exponential curve. Epv With T Esv If the deviation is smaller than the system preset dead zone, such as 0.3°C, the valve will not operate.

[0062] The specific implementation process of this embodiment includes:

[0063] (1) The startup process control method of the refrigeration system determines whether the exhaust temperature reaches the ambient temperature + exhaust temperature return difference. If it does not reach it, the main valve gradually decreases according to the exponential law. If it reaches it, it switches to superheat control.

[0064] (2) The main valve superheat adjustment method uses the difference between the evaporator outlet temperature and the inlet temperature as the superheat to determine whether the superheat is within the target superheat ± dead zone value range. If it is within the range, the main valve does not operate. If the actual superheat is greater than the target superheat + dead zone value, the main valve opening increases exponentially. If the actual superheat is less than the target superheat - dead zone value, the main valve opening decreases exponentially.

[0065] (3) The auxiliary valve is used as a bypass valve and cooperates with the main control PID program to perform temperature control. When the measured temperature approaches the target temperature downward (or upward), it is determined whether the measured temperature is greater than the target temperature + dead zone value. If it is greater, the valve opening is reduced exponentially. If the measured temperature is less than the target temperature - dead zone value, the valve opening is increased exponentially.

[0066] (4) Adjust the auxiliary valve adaptive energy control method to determine whether the measured temperature is less than the target temperature + dead zone value and greater than the measured temperature - dead zone value. If so, calculate the mean square error of the measured temperature within 5 minutes. If the mean square error is less than the preset value of 0.3°C, determine whether the current operating frequency of the compressor is greater than the minimum frequency and whether the auxiliary valve opening is greater than zero. If so, reduce the auxiliary valve opening according to the preset cycle and small steps.

[0067] (5) The opening increment of the electronic expansion valve follows an exponential law Changes, and limits the maximum value of the increment y to the maximum allowed value of the system, and the minimum value to the minimum allowed value of the system.

[0068] (6) The time interval for adjusting the opening of the electronic expansion valve follows an exponential law Change, the time unit is minutes, and the maximum value of y is limited to 45 minutes and the minimum value is 0.1 minutes.

[0069] (7) One-button PID parameter self-tuning method: one-button operation sets the self-tuning flag to true value and enters the self-tuning mode. First, the compressor is set to operate at the lowest frequency, then the main valve is set to the preset opening, and then the auxiliary valve is adjusted to 0% opening. Then the timing is started. At the same time, it is determined that the mean square error of the measured temperature within 5 minutes is less than the preset value. Then the inflection point calculation method is called to calculate the PID parameters. Finally, it is determined whether the calculation result is valid. If it is valid, the original parameters are updated. If it is invalid, the self-tuning mode is directly exited.

[0070] This embodiment realizes a quick response after the refrigeration system is started; the one-button PID parameter self-tuning control logic of this embodiment can obtain better control parameters to achieve higher precision control, and can effectively control the deviation between the temperature and the target temperature within ±0.1°C; the superheat control method of the main valve of this embodiment makes the refrigerant heat exchange more sufficient to obtain a better refrigeration effect; the bypass adjustment of the auxiliary valve of this embodiment can effectively reduce the overshoot in the temperature response process, and more effectively reduce energy consumption in the constant temperature process. The one-button parameter self-tuning logic of this embodiment makes its implementation plan simpler and has higher application significance.

[0071] like Figure 1 As shown, when the system starts, it is first determined whether the compressor exhaust temperature is greater than the ambient temperature + exhaust temperature hysteresis. If not, the main valve gradually reduces its opening according to the exponential law. If it has reached, the program switches to superheat control. Among them, the exhaust temperature hysteresis is a system parameter that can be modified. In the control method proposed in this embodiment, at an ambient temperature of 25-40℃, the exhaust temperature hysteresis value of 40℃ is more appropriate.

[0072] like Figure 2 As shown, the system follows Figure 1 The method starts executing after the startup is completed Figure 2 The control logic performs superheat control. A dead zone value such as 0.2°C is preset in the superheat control program. This value should not be too large or too small, otherwise it will affect the accuracy of the final controlled temperature of the system. Figure 2 As shown in the figure, if the measured actual superheat > target superheat process + dead zone value, the main valve increases the opening according to the cycle and step size obtained by the exponential law; if the measured actual superheat < target superheat process - dead zone value, the main valve decreases the opening according to the cycle and step size obtained by the exponential law; if the actually measured superheat is within the dead zone value range, the main valve does not operate to avoid frequent operations affecting the system control accuracy.

[0073] like Figure 3 The auxiliary valve bypass adjustment logic shown in the figure is used to return the refrigerant directly to the compressor before passing through the evaporator, reducing the refrigerant entering the evaporator, thereby reducing the cooling capacity, which can effectively reduce the overshoot phenomenon that occurs when the controller 1 executes the PID program to control the temperature to drop and approach the target temperature; because the variable frequency compressor has a minimum operating frequency, in some application scenarios, when the compressor is at the minimum operating frequency, the actual temperature is still lower than the target temperature. Figure 3 The auxiliary valve bypass adjustment can effectively reduce the cooling capacity and avoid excessively low temperature.

[0074] like Figure 4As shown in the figure, the adaptive energy-saving control logic, if the controlled temperature is less than the target temperature + dead zone value, and greater than the target temperature - dead zone value, and the mean square error in the past 5 minutes is less than the preset value, it can be judged that the temperature has entered a stable state. At this time, the compressor operating frequency is judged. If its operating frequency is greater than the minimum frequency and the auxiliary valve opening is greater than zero, it means that the excess cooling capacity generated at the current operating frequency is bypassed back to the compressor. At this time, according to Figure 4 The control logic gradually closes the auxiliary valve opening according to the preset cycle and small steps, such as Figure 4 In the control logic, the 5-minute time for calculating the mean square error can be modified as a system operating parameter. It is more appropriate to use a 5-minute calculation for the control method proposed in this embodiment; the valve adjustment cycle and step size can be modified as system operating parameters. In order to achieve the control accuracy of the control method proposed in this embodiment, the small step size should not be too large, and it is usually more appropriate to take a 1% opening.

[0075] like Figure 5 The one-button PID parameter self-tuning method proposed in this embodiment is shown. The program scans whether the self-tuning flag is set. If the flag is set to a true value, the compressor is set to run at the lowest frequency, and the main valve is adjusted to a preset opening. The opening can be modified as a system parameter. The method proposed in this embodiment is set to 30% opening, which is more appropriate. Then the auxiliary valve opening is set to zero, and the timing is started to determine the mean square error of the controlled temperature within 5 minutes. If the mean square error is less than the preset value, it is also set as a system parameter that can be modified. The method proposed in this embodiment uses 0.5°C, which is more appropriate. If the controlled temperature meets the mean square error, the inflection point method PID parameter self-tuning program is called. After the self-tuning program is executed, it is determined whether the calculation result is valid. If it is valid, the PID parameters are updated. If it is invalid, the tuning mode is directly exited.

[0076] One-button PID parameter self-tuning process, the self-tuning mark is a variable in the program operation, which can be controlled by the operation button. Press the button to set the self-tuning mark to the TRUE value, and then enter the parameter self-tuning mode. First, set the compressor operating frequency to the lowest frequency, and then set the main valve to a fixed opening. The opening can be modified as a system parameter. Then, the auxiliary valve opening is set to zero. The system starts to run in this mode and starts timing. At the same time, it determines whether the mean square error of the measured temperature within 5 minutes is less than the preset value. The 5-minute time can be modified in advance as a system parameter. When the mean square error of the measured temperature is less than the preset value, it is determined that the temperature has entered a steady state, and the inflection point method PID parameter tuning program is called to calculate the PID parameters. The tuning program is executed and it is determined whether the parameters are valid. If valid, the original PID parameters are updated and the tuning mode is exited. If invalid, the tuning mode is directly exited.

[0077] like Figure 6 As shown, it is the relationship between adjusting the opening of the electronic expansion valve and the controlled temperature deviation, according to the exponential law: Change, y is the increment of each adjustment of the valve opening, x is the difference between the measured temperature and the target temperature, where A1 and B1 are system parameters that can be modified. In the control method proposed in this embodiment, B1=0.8 and B1=0.5 are more appropriate, indicating that when the temperature deviation is greater, the increment of the valve opening is greater for each adjustment, and the smaller the deviation is, the smaller the opening is for each adjustment. When the calculated result of the valve opening increment is greater than 100%, it is opened at 100%, and if the calculated result of the valve opening increment is less than 0, it is opened at 0%. At the same time, a dead zone value can be set for the horizontal axis temperature deviation value x. If x is within the dead zone value range, there is no need to calculate the valve opening increment according to the exponential law, and the valve does not need to act.

[0078] like Figure 7 As shown, it is the relationship between the electronic expansion valve adjustment cycle and temperature deviation, according to the exponential law: Change, y is the time interval of each valve adjustment, that is, the adjustment cycle, in minutes, x is the difference between the measured temperature and the target temperature, where A2 and B2 are system parameters that can be modified. In the control method proposed in this embodiment, A2=50 and B2=0.4 are more suitable. When the calculated result y is greater than 45 minutes, it is adjusted according to a 45-minute cycle. If the calculated result valve opening increment is less than 0.1 minutes, it is adjusted according to a 0.1-minute cycle. At the same time, the horizontal axis x temperature deviation value can set a dead zone value. If x is within the dead zone value range, there is no need to calculate the adjustment cycle according to the exponential law, and the valve does not need to act. The main electronic expansion valve and the auxiliary electronic expansion valve can take different parameters A and B according to system requirements.

[0079] like Figure 8 As shown, the controller is a microprocessor that runs the program compiled by the control method proposed in this embodiment. It can detect temperature by writing a program, control the working frequency of the variable frequency compressor through RS485 communication, drive the electronic expansion valve to adjust the opening, control the speed of the fan in the condenser, and control the speed of the fan in the evaporator. The controller runs the programs of the above-mentioned various links in the control method proposed in this embodiment.

[0080] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A control method using an adaptive energy-saving refrigeration constant temperature control system, characterized in that: include: The system comprises a controller and a refrigeration system, wherein the refrigeration system comprises a refrigeration circuit composed of a compressor, a condenser, a drying filter, a switch type solenoid valve, a main valve and an evaporator which are connected in series in sequence, and the exhaust port of the compressor is connected to the inlet of the evaporator through a secondary valve; The evaporator is installed in the controlled device, and the exhaust port of the compressor, the inlet and outlet of the evaporator and the controlled device are all equipped with temperature sensors; The compressor, condenser, filter drier, switch type solenoid valve, main valve, auxiliary valve, evaporator and each of the temperature sensors are electrically connected to the controller; The controller integrates a microprocessor, a storage, a digital-to-analog converter, an RS485 communication circuit, an electronic expansion valve drive circuit and a power supply circuit; The control method comprises: Step 1: starting the refrigeration system, obtaining the exhaust temperature of the compressor and the ambient temperature in the refrigeration system, and controlling the opening of the main valve in the refrigeration system based on a comparison result between the exhaust temperature and the ambient temperature; Step 2: After the main valve control is completed, the real-time temperature of the controlled equipment in the refrigeration system is obtained based on the preset PID program, and it is determined whether the real-time temperature reaches the preset target temperature, and the opening of the auxiliary valve in the refrigeration system is controlled based on the determination result; Step 3: After the auxiliary valve control is completed, the auxiliary valve is adaptively controlled for energy saving based on the real-time temperature and the operating frequency of the compressor; Step 4: After the adaptive energy-saving control is completed, start the self-tuning mode, which includes: The compressor, the main valve and the auxiliary valve in the refrigeration system are operated in a preset mode, and the real-time temperature within a preset period is obtained, and the mean square error of the real-time temperature within the preset period is calculated. If the mean square error is less than a preset threshold, the parameters of the preset PID program are updated, and the constant temperature control of the refrigeration system for the next period is performed based on the PID program after the parameter update; if the mean square error is greater than the preset threshold, the self-tuning mode is terminated, and the constant temperature control of the refrigeration system for the next period is performed based on the original preset PID program.

2. A control method using an adaptive energy-saving refrigeration constant temperature control system according to claim 1, characterized in that: The controlling of the opening degree of the main valve in the refrigeration system specifically includes: When the exhaust temperature is lower than the sum of the ambient temperature and the preset exhaust temperature hysteresis value, reducing the opening of the main valve; When the exhaust temperature is greater than the sum of the ambient temperature and the preset exhaust temperature hysteresis value, main valve superheat control is performed.

3. A control method using an adaptive energy-saving refrigeration constant temperature control system according to claim 2, characterized in that: The process of executing the main valve superheat control specifically includes: Calculate the difference between the outlet and inlet temperatures of the evaporator in the refrigeration system to obtain the superheat; When the superheat is greater than the sum of a preset target superheat and a preset dead zone value, increasing the opening of the main valve; When the superheat is less than the difference between the preset target superheat and the preset dead zone value, the opening of the main valve is reduced.

4. The control method using the adaptive energy-saving refrigeration constant temperature control system according to claim 1 is characterized in that: The controlling of the opening degree of the auxiliary valve in the refrigeration system specifically includes: When the real-time temperature is greater than the sum of the preset target temperature and the preset dead zone value, reducing the opening of the auxiliary valve; When the real-time temperature is less than the difference between the preset target temperature and the preset dead zone value, the opening of the auxiliary valve is increased.

5. The control method using the adaptive energy-saving refrigeration constant temperature control system according to claim 1 is characterized in that: The adaptive energy-saving control of the auxiliary valve based on the real-time temperature and the operating frequency of the compressor specifically includes: The mean square error value of the real-time temperature within a preset period is measured. When the mean square error value is less than the preset value, the operating frequency of the compressor is greater than the preset operating frequency and the auxiliary valve opening is greater than zero, the auxiliary valve opening is reduced according to the preset period and small steps.

6. A control method using an adaptive energy-saving refrigeration constant temperature control system according to claim 1, characterized in that: During the process of controlling the opening of the main valve and the auxiliary valve, the opening increment and adjustment time interval corresponding to each valve both conform to the exponential law.

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