Two-parameter electronic expansion valve control system and control method thereof

Abstract

The invention discloses a two-parameter electronic expansion valve control system and a control method thereof. The two-parameter electronic expansion valve control system comprises a temperature sensor, a pressure sensor and a control unit, wherein the control unit is used for being connected with the sensors, collecting data in real time, calculating relevant parameters and dynamically adjusting the system according to preset conditions; the control unit comprises a suction pressure control module, an exhaust superheat degree control module and a correction module; through a two-parameter control method of suction pressure and exhaust superheat degree, precise adjustment of the electronic expansion valve is achieved; at the initial stage of starting, the system is ensured to quickly enter a stable state through suction pressure control; in the transition stage, intelligent switching of control modes is achieved by monitoring the exhaust temperature and the exhaust superheat degree; in the exhaust superheat degree control stage, the system performance is further optimized by dynamically correcting a set value, a PID control algorithm and a fuzzy calculation method are combined in the whole control process, and the intelligent level and adaptability of the system are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of industrial control, and particularly to a dual-parameter electronic expansion valve control system and a control method thereof. Background Art

[0002] In the prior art, the control of an electronic expansion valve usually uses the suction superheat or the discharge superheat as a single parameter for adjustment. In addition, there are also technical solutions that combine the suction and discharge superheats for comprehensive control. In flooded and falling film water chillers, the application of discharge superheat control for the electronic expansion valve is relatively widespread. However, in the initial stage of system startup, due to the lag in the detection of the discharge temperature, it is impossible to effectively use the discharge superheat for control. To solve this problem, some alternative solutions have been adopted in the prior art, such as maintaining a fixed opening of the electronic expansion valve during startup or controlling it according to a preset startup curve. However, these methods have obvious limitations. Since different models of electronic expansion valves and units with different energy levels have significant differences in the requirements for control parameters, it is impossible to use unified parameters for control. This may lead to problems such as low pressure or oil carryover during startup, thereby affecting the operating life of the compressor. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to provide a dual-parameter electronic expansion valve control system that solves the problems of single parameter and temperature lag in the prior art. The second object of the present invention is to provide a control method for the dual-parameter electronic expansion valve control system to improve the safety, stability, and economy of the system.

[0004] Technical Solution: A dual-parameter electronic expansion valve control system according to the present invention includes a temperature sensor, a pressure sensor, and a control unit for connecting with the sensors, collecting data in real time, calculating relevant parameters, and dynamically adjusting the system according to preset conditions; the control unit includes a suction pressure control module, a discharge superheat control module, and a correction module; the temperature sensor and the pressure sensor are respectively installed at the discharge port, the suction port of the compressor, and the water outlet of the refrigeration system, and are electrically connected to the control unit.

[0005] Preferably, the suction pressure control module is used to control the opening of the electronic expansion valve according to the suction pressure P2 in the initial stage of startup; the discharge superheat control module is used to control the opening of the electronic expansion valve according to the discharge superheat Tcg after the system runs stably.

[0006] Preferably, the correction module is used to dynamically correct the set value Tcgs of the discharge superheat according to the change of the suction pressure P2.

[0007] Preferably, the control unit dynamically adjusts the opening degree of the electronic expansion valve according to the deviation of the suction pressure P2 or the exhaust superheat degree Tcg through the PID control algorithm.

[0008] Preferably, the control unit further includes a circuit board, and the circuit board can adapt to multiple units and implement specific functions.

[0009] The control method of a dual-parameter electronic expansion valve control system according to the present invention includes the following steps:

[0010] S1. The exhaust temperature T1, the suction temperature T2, and the water outlet temperature T5 of the compressor are collected in real time by the temperature sensor; the exhaust pressure P1 and the suction pressure P2 are collected in real time by the pressure sensor; the condensation temperature Tc, the evaporation temperature Te, the exhaust superheat degree Tcg, the low-pressure set value Pes, the upper limit Pemax of low-pressure operation, the lower limit Pemin of low-pressure operation, the exhaust superheat degree set value Tcgs, and the pressure set value Pes are obtained through calculation;

[0011] S2. The system dynamically adjusts the opening degree of the electronic expansion valve according to the suction pressure deviation ΔP through the PID control algorithm, so that the suction pressure P2 satisfies between the lower limit Pemin of low-pressure operation and the upper limit Pemax of low-pressure operation; the suction pressure deviation ΔP is the difference between the suction pressure P2 and the pressure set value Pes;

[0012] S3. It is judged whether the system enters a stable state through a preset condition, and the preset condition is that the exhaust superheat degree Tcg is greater than the exhaust superheat degree set value Tcgs;

[0013] S4. The system dynamically adjusts the opening degree of the electronic expansion valve according to the deviation ΔT between the exhaust superheat degree Tcg and the exhaust superheat degree set value Tcgs through the PID control algorithm;

[0014] S5. The system dynamically corrects the exhaust superheat degree set value Tcgs according to the change of the suction pressure P2. When the suction pressure P2 is not between the lower limit Pemin of low-pressure operation and the upper limit Pemax of low-pressure operation, the pressure deviation table is searched to correct the exhaust superheat degree set value Tcgs, and the cycle detection method is used for cyclic detection until the suction pressure P2 is between the lower limit Pemin of low-pressure operation and the upper limit Pemax of low-pressure operation.

[0015] Preferably, in the step S1, the acquisition frequencies of the temperature sensor and the pressure sensor match the response time of the system.

[0016] Preferably, in the step S2, the parameters of the PID control algorithm are dynamically adjusted according to the actual operating conditions of the system.

[0017] Preferably, in the step S5, the pressure deviation table is generated based on historical operation data and fuzzy calculation methods.

[0018] Preferably, in the step S5, the detection period of the periodic detection method is dynamically adjusted according to the actual operation state of the system.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: By introducing the dual-parameter control method of pressure and superheat degree, the lag in exhaust temperature detection at the initial stage of startup is effectively overcome; it can be flexibly adjusted according to different working conditions, avoiding problems such as low pressure or oil leakage caused by parameter mismatch, significantly improving the stability and reliability of the system, effectively optimizing the system operation performance, and enhancing the energy-saving effect of the system. Description of the Drawings

[0020] Figure 1 It is a control flow chart of the present invention. Detailed Embodiments

[0021] The technical solutions of the present invention will be further described below with reference to the drawings.

[0022] The present invention mainly includes four stages: system initialization and initial startup control, transition stage and control mode switching, exhaust superheat degree control stage, and system stable operation and optimization, which are specifically as follows:

[0023] The first stage is system initialization and initial startup control

[0024] System initialization; after the unit is started up, the system first collects relevant data through temperature sensors and pressure sensors. Specifically, it includes: the exhaust temperature T1 at the exhaust port of the compressor, the suction temperature T2 at the suction port of the compressor, the water outlet temperature T5 at the water outlet of the refrigeration system, the exhaust pressure P1 of the compressor, and the suction pressure P2 of the compressor. By comprehensively collecting the key parameters in the initial stage of system operation, it provides basic data support for subsequent control strategies, ensuring that the system can quickly respond and enter a stable operation state. The condensation temperature Tc and the evaporation temperature Te are obtained by combining the exhaust pressure P1 and the suction pressure P2 with the pressure-enthalpy diagram of the refrigerant or relevant formulas, and then the exhaust superheat degree Tcg is obtained through formula calculation. The calculation formula is: Tcg = T1 - Tc. According to the set temperature T, the temperature deviation ΔT, and the condensation pressure P, the low-pressure set value Pes, the upper limit Pemax of low-pressure operation, the lower limit Pemin of low-pressure operation, and the preset exhaust superheat degree set value Tcgs are calculated. The specific calculation formulas are:

[0025] Pes = h(T, K), where h is a function for calculating the low-pressure set value;

[0026] Pemax = i(T, K, ΔT), where i is a function for calculating the upper limit of low-pressure operation;

[0027] Pemin = j(T, K, ΔT), where j is a function for calculating the lower limit of low-pressure operation;

[0028] Tcgs = k(Tcg, P), where k is a function for calculating the set value of the preset exhaust superheat degree.

[0029] The system determines the control range of the suction pressure P2 according to the load and the unit design parameters, including setting the lower limit value Pemin of low-pressure operation and the upper limit value Pemax of low-pressure operation. Among them, the lower limit value Pemin of low-pressure operation is used to prevent the efficiency decline caused by too low suction pressure, and the upper limit value Pemax of low-pressure operation is used to prevent the compressor liquid slugging or system overload caused by too high suction pressure.

[0030] In the initial stage of startup, the main control objective of the system is to maintain the suction pressure P2 within the preset working range of the suction pressure. The system compares the detected current suction pressure P2 with the lower limit value Pemin of low-pressure operation. When the detected suction pressure P2 is lower than the lower limit value Pemin of low-pressure operation, it indicates that the system needs to increase the refrigerant flow rate to increase the suction pressure. At this time, the system calculates the opening adjustment amount of the electronic expansion valve through the PID control algorithm, and the formula is as follows:

[0031] ΔV = Kp×ΔP + Ki×∫ΔP dt + Kd×dΔP / dt

[0032] Among them, ΔV is the change amount of the opening of the electronic expansion valve, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, and ΔP is the suction pressure deviation ΔP = P2 - Pes. The present invention adopts the PID control algorithm to dynamically adjust the opening of the electronic expansion valve according to the suction pressure deviation, ensuring that the suction pressure P2 quickly and stably approaches the pressure set value Pes and realizing precise control.

[0033] The second stage is the transition stage and the control mode switching:

[0034] When the suction pressure P2 meets the working range of the suction pressure, the system enters the transition stage. First, it is necessary to determine whether the system enters a stable state. The system will judge whether one of the two conditions is met, namely Condition 1: The discharge temperature T1 is basically stable, that is, the change within 1 minute does not exceed 2°C; Condition 2: The superheat degree of discharge Tcg is greater than the set target value Tcgs. If any one of the above two conditions is met, the system will trigger the switching of the control strategy, switching from the control based on the suction pressure P2 to the control based on the superheat degree of discharge Tcg. Among them, Condition 1: The discharge temperature T1 reflects the operating state of the compressor and the circulation of the refrigerant in the system. When the change of the discharge temperature T1 within 1 minute does not exceed 2°C, it can be considered that the discharge temperature T1 has been basically stable. This judgment standard is set based on actual operating experience. At this time, the switching of the control strategy can avoid control errors caused by system fluctuations. Condition 2: The superheat degree of discharge Tcg is the difference between the compressor discharge temperature T1 and the condensation temperature Tc, that is, Tcg = T1 - Tc. The superheat degree target value Tcgs of discharge is preset according to the system design and operating requirements to ensure that the system operates in an efficient and safe state. The present invention preferably uses the superheat degree of discharge Tcg greater than the set target value Tcgs to determine whether the system enters a stable state.

[0035] The third stage is the superheat degree of discharge control stage

[0036] After switching to the superheat degree of discharge control mode, the system dynamically adjusts the opening of the electronic expansion valve according to the deviation ΔT = Tcg - Tcgs between the superheat degree of discharge Tcg and the set target value Tcgs through the PID control algorithm. The superheat degree of discharge control can more accurately reflect the operating state of the system, ensure that the system operates in an efficient and safe state, and further optimize the system performance. Such as Figure 1As shown, the set value of the exhaust superheat is dynamically corrected. The system dynamically corrects the set value of the exhaust superheat Tcgs according to the change of the suction pressure P2: when the suction pressure P2 is less than the lower limit of low-pressure operation Pemin, it indicates that the set value of the exhaust superheat Tcgs is too large, and the set value is corrected by looking up the pressure deviation table Tcgs' = Tcgs - ΔTcgs; when the suction pressure P2 is greater than the upper limit of low-pressure operation Pemax, it indicates that the set value of the exhaust superheat Tcgs is too small, and the set value is corrected by looking up the pressure deviation table Tcgs' = Tcgs + ΔTcgs. By dynamically correcting the set value of the exhaust superheat Tcgs, the system can adapt to the operating requirements under different working conditions, and avoid system fluctuations or efficiency degradation caused by unreasonable set value of the exhaust superheat Tcgs. Further, the pressure deviation table is generated based on the fuzzy calculation method, which specifically includes the following steps: collecting the pressure deviation and its change rate data in the refrigeration system; performing fuzzy processing on the collected pressure deviation and change rate data to convert them into fuzzy sets; establishing a fuzzy control rule base according to the fuzzy sets, and the rule base is stored in the form of a table, recording the output control quantities under different combinations of pressure deviation and change rate; calculating the output fuzzy control quantity through fuzzy inference and converting it into a clear control signal by using the defuzzification method. Among them, the defuzzification method preferably adopts the maximum membership degree method to convert the fuzzy output into a specific control signal; generating a pressure deviation table according to the fuzzy inference result, and the table records the pressure deviation and its corresponding control strategy under different input conditions. Through the fuzzy calculation method, the uncertainty in the system operation can be processed, and the generated pressure deviation table provides a scientific basis for the dynamic correction of the set value of the exhaust superheat, further improving the intelligent level and adaptability of the system

[0037] The fourth stage is the stable operation and optimization of the system

[0038] In the exhaust superheat control mode, the system continuously monitors the suction pressure P2 and the exhaust superheat Tcg, and dynamically adjusts the opening of the electronic expansion valve according to the real-time data. When the suction pressure P2 is within the control range from Pemin to Pemax, the set value of the exhaust superheat Tcgs remains unchanged, and the system maintains stable operation through the PID control algorithm. Through the dual-parameter control of pressure and exhaust superheat, the system can achieve precise adjustment under different working conditions, optimize the system performance, improve the operation efficiency, extend the equipment life, and reduce the energy consumption

[0039] Through the dual-parameter control method of suction pressure and discharge superheat, the precise adjustment of the electronic expansion valve is achieved. In the initial stage of startup, the suction pressure control is used to ensure that the system quickly enters a stable state; in the transition stage, the intelligent switching of the control mode is realized by monitoring the discharge temperature and discharge superheat; in the discharge superheat control stage, the system performance is further optimized by dynamically correcting the set value. The entire control process combines the PID control algorithm and the fuzzy calculation method, significantly improving the intelligent level and adaptability of the system, and solving the problems of control lag in the initial stage of startup and poor adaptability to different working conditions existing in the prior art.

Claims

1. A dual-parameter electronic expansion valve control system, characterized in that: It includes a temperature sensor, a pressure sensor and a control unit connected to the sensors for real-time data collection, calculation of relevant parameters, and dynamic adjustment of the system according to preset conditions; the control unit includes an intake pressure control module, an exhaust superheat control module and a correction module; the temperature sensor and the pressure sensor are respectively installed at the exhaust port, intake port and water outlet of the compressor, and are electrically connected to the control unit.

2. The dual-parameter electronic expansion valve control system according to claim 1, characterized in that: The suction pressure control module is used to control the opening of the electronic expansion valve according to the suction pressure P2 at the initial startup; the exhaust superheat control module is used to control the opening of the electronic expansion valve according to the exhaust superheat Tcg after the system runs stably.

3. The dual-parameter electronic expansion valve control system according to claim 1, characterized in that: The correction module is used to dynamically correct the exhaust superheat setting value Tcgs according to the change of the suction pressure P2.

4. The dual-parameter electronic expansion valve control system according to claim 1, characterized in that: The control unit dynamically adjusts the opening of the electronic expansion valve according to the deviation of the suction pressure P2 or the exhaust superheat Tcg through the PID control algorithm.

5. The dual-parameter electronic expansion valve control system according to claim 1, characterized in that: The control unit also includes a circuit board, which can be adapted to various units and realize specific functions.

6. A control method using the dual-parameter electronic expansion valve control system according to claim 1, characterized in that: The following steps are involved: S1. Collect the exhaust temperature T1, suction temperature T2 and outlet water temperature T5 of the compressor in real time according to the temperature sensor; collect the exhaust pressure P1 and suction pressure P2 in real time according to the pressure sensor; obtain the condensation temperature Tc, evaporation temperature Te, exhaust superheat Tcg, low pressure setting value Pes, low pressure operation upper limit Pemax, low pressure operation lower limit Pemin, exhaust superheat setting value Tcgs and pressure setting value Pes by calculation; S2. The system uses a PID control algorithm to dynamically adjust the opening of the electronic expansion valve according to the suction pressure deviation ΔP, so that the suction pressure P2 satisfies the low-pressure operation lower limit Pemin and the low-pressure operation upper limit Pemax; the suction pressure deviation ΔP is the difference between the suction pressure P2 and the pressure setting value Pes; S3. Determine whether the system enters a stable state according to a preset condition, wherein the preset condition is that the exhaust superheat Tcg is greater than the exhaust superheat setting value Tcgs; S4, the system dynamically adjusts the opening of the electronic expansion valve through the PID control algorithm according to the deviation ΔT between the exhaust superheat Tcg and the exhaust superheat set value Tcgs; S5. The system dynamically corrects the exhaust superheat setting value Tcgs according to the change of the suction pressure P2. When the suction pressure P2 is not between the low-pressure operation lower limit Pemin and the low-pressure operation upper limit Pemax, the system looks up the pressure deviation table to correct the exhaust superheat setting value Tcgs, and uses a periodic detection method to perform cyclic detection until the suction pressure P2 is between the low-pressure operation lower limit Pemin and the low-pressure operation upper limit Pemax.

7. The control method according to claim 6, characterized in that: In the step S1, the acquisition frequency of the temperature sensor and the pressure sensor matches the response time of the system.

8. The control method according to claim 6, characterized in that: In step S2, the parameters of the PID control algorithm are dynamically adjusted according to the actual operating conditions of the system.

9. The control method according to claim 6, characterized in that: In step S5, the pressure deviation table is generated based on historical operation data and fuzzy calculation method.

10. The control method according to claim 6, characterized in that: In step S5, the detection period of the period detection method is dynamically adjusted according to the actual operating state of the system.

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