CN115325783B - Control system of heat pump drying system for preserved fruits - Google Patents
Control system of heat pump drying system for preserved fruits Download PDFInfo
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- CN115325783B CN115325783B CN202210857223.4A CN202210857223A CN115325783B CN 115325783 B CN115325783 B CN 115325783B CN 202210857223 A CN202210857223 A CN 202210857223A CN 115325783 B CN115325783 B CN 115325783B
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- heat pump
- heat exchanger
- stop valve
- frequency
- drying
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B9/00—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards
- F26B9/06—Machines or apparatus for drying solid materials or objects at rest or with only local agitation; Domestic airing cupboards in stationary drums or chambers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B30/00—Heat pumps
- F25B30/02—Heat pumps of the compression type
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B41/00—Fluid-circulation arrangements
- F25B41/20—Disposition of valves, e.g. of on-off valves or flow control valves
- F25B41/24—Arrangement of shut-off valves for disconnecting a part of the refrigerant cycle, e.g. an outdoor part
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B41/00—Fluid-circulation arrangements
- F25B41/30—Expansion means; Dispositions thereof
- F25B41/31—Expansion valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/06—Controlling, e.g. regulating, parameters of gas supply
- F26B21/08—Humidity
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/06—Controlling, e.g. regulating, parameters of gas supply
- F26B21/10—Temperature; Pressure
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B25/00—Details of general application not covered by group F26B21/00 or F26B23/00
- F26B25/06—Chambers, containers, or receptacles
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P60/00—Technologies relating to agriculture, livestock or agroalimentary industries
- Y02P60/80—Food processing, e.g. use of renewable energies or variable speed drives in handling, conveying or stacking
- Y02P60/85—Food storage or conservation, e.g. cooling or drying
Abstract
The application relates to the technical field of heat pump drying, in particular to a heat pump drying system for preserved fruits and a control system thereof. The heat pump drying system can adjust the working frequency of the compressor and the working frequency of the fan by adopting the frequency converter so as to adjust the flow of the refrigerant and the drying air quantity, thereby realizing the adjustment according to the requirement. The control system of the application adopts the fuzzy principle-based control of the frequency of the compressor, the opening degree of the second expansion stop valve and the opening degree of the first expansion stop valve, and the PID proportion control is adopted to adjust the opening degree of the moisture discharging port, and the design of the fuzzy rule table is designed based on the negative feedback principle and expert experience. The intelligent control strategy and the Internet of things technology are adopted to solve the problems of low control precision, poor disturbance resistance, low informatization and the like in the existing heat pump drying system, the automation and intelligent level is improved, and the main indexes of energy conservation, product quality improvement, high efficiency and reliability of the system are realized.
Description
Technical Field
The application relates to the technical field of heat pump drying, in particular to a control system of a heat pump drying system for preserved fruits.
Background
The working principle of heat pump drying is that the heat pump provides heat energy to heat the drying working medium (air), and the moisture of the drying material is gradually separated from the surface through the action of the drying working medium and the drying material, so that the drying purpose is realized. The heat pump drying system is composed of a heat pump system and a drying chamber, wherein the heat pump system mainly comprises a compressor, an expansion valve, an evaporator, a condenser and the like. The heat pump can work in a heating mode and a refrigerating mode, so that the free setting of the drying temperature in the material drying process can be realized, and the different drying process temperature requirements are met. Compared with the traditional mode of obtaining heat energy by burning fossil energy, the heat pump has the remarkable advantages of no pollution, high efficiency and the like, and is focused and widely researched and applied as a new energy technology.
Heat pump drying is a complex process control system, and the working process involves process variables such as evaporator temperature, refrigerant flow and pressure, drying room temperature humidity, drying air speed, etc., and actuators in the system include compressors, expansion valves, fans, electric heaters, on-off actuators, etc. The heat pump drying is applied to the food fields of preserved fruits (dried fruits) and the like, and higher requirements are put on the quality of dried foods and the energy efficiency of a drying system.
Disclosure of Invention
In order to solve the problems, and meet the requirements of high precision, high disturbance rejection and equipment intellectualization of controlled quantity in a drying process, the application provides a control system of a heat pump drying system for preserved fruits, which comprises the following specific technical scheme:
the heat pump drying system for the preserved fruits comprises a heat pump subsystem, a drying chamber and a frequency converter, wherein the heat pump subsystem comprises a first heat exchanger, a first expansion stop valve, a second expansion stop valve, a four-way reversing valve, a second heat exchanger and a compressor;
the second heat exchanger is arranged at the top of the drying chamber, and the first heat exchanger, the first expansion stop valve, the second expansion stop valve and the second heat exchanger are sequentially connected; the four-way reversing valve is respectively connected with the second heat exchanger, the compressor and the first heat exchanger;
the top of the drying chamber is also provided with a fan and an electric heater, the upper part of the drying chamber is provided with a moisture discharging port, the lower part of the drying chamber is provided with a drying material rack, the lower part of the drying chamber is provided with a weight sensor, and the drying chamber is also provided with a humidity sensor and a temperature sensor;
the compressor and the fan are respectively connected with a frequency converter, and the frequency converter is used for adjusting the working frequency of the compressor and the working frequency of the fan so as to adjust the flow of the refrigerant and the dry air quantity;
the working modes of the heat pump subsystem comprise a heating mode and a refrigerating mode, when the heat pump subsystem works in the heating mode, the second heat exchanger is a condenser, and the first heat exchanger is an evaporator; when operating in the cooling mode, the second heat exchanger is an evaporator and the first heat exchanger is a condenser.
The control system for the heat pump drying system for the preserved fruits is applied to the heat pump drying system and comprises a PLC (programmable logic controller), a data acquisition module, a human-machine interface HMI and a cloud platform;
the data acquisition module is connected with a humidity sensor, a temperature sensor, a weight sensor and the heat pump subsystem of the heat pump drying system, and is used for acquiring operation condition data of the heat pump subsystem, temperature and humidity in the drying chamber and weight of the drying material rack, and transmitting the acquired data to the PLC; the PLC is respectively connected with the frequency converter, the first expansion stop valve, the second expansion stop valve and the moisture outlet actuator, the moisture outlet actuator is connected with the moisture outlet, and the PLC is used for controlling the opening of the moisture outlet according to the expert database, the fuzzy rule and the PID control rule, controlling the opening of the first expansion stop valve and the second expansion stop valve so as to regulate the flow of the refrigerant and controlling the frequency of the frequency converter;
the human-machine interface HMI is connected with the PLC and used for carrying out human-machine interaction;
the cloud platform is connected with the human-machine interface HMI and is used for monitoring the operation condition of the heat pump drying system and storing monitoring data.
Preferably, the cloud platform comprises an MQTT message proxy server and a database server, wherein the human-machine interface HMI is connected with the MQTT message proxy server and distributes equipment running state and fault information to the client through an MQTT protocol; the database server is used for storing data and providing data services.
Preferably, the PLC controls the operation condition of the heat pump drying system according to an expert database, and the expert database stores the temperature and humidity of preserved fruit drying, the water content of materials, the drying time, the energy efficiency of the system and the superheat degree of a compressor, a fan, a first heat exchanger or a second heat exchanger.
Preferably, the PLC adjusts the frequency of the frequency converter and the opening degrees of the first expansion stop valve and the second expansion stop valve according to a fuzzy rule, when the frequency of the frequency converter is adjusted, the input variable is a temperature error value between the temperature in the drying chamber and the set temperature, and the output value is the frequency of the frequency converter;
when the opening degrees of the first expansion stop valve and the second expansion stop valve are adjusted, the input amount is an error between the superheat degree of the first heat exchanger or the second heat exchanger and the set superheat degree, and the output is the opening degrees of the first expansion stop valve and the second expansion stop valve.
Preferably, the PLC controller adopts PID control rule to control the moisture discharging port actuator, so as to adjust the opening degree of the moisture discharging port, specifically, the error value between the set humidity of the drying chamber and the actual humidity measured by the humidity sensor is input into the PLC controller, and the opening degree of the moisture discharging port is output to adjust the humidity of the drying chamber.
Preferably, in the fuzzy rule that the PLC controller adjusts the frequency of the frequency converter, the input variable is an error value of the set temperature, and the language variable is expressed as: negative big, negative medium, negative small, zero, positive small, medium and positive big, respectively denoted as NL, NM, NS, Z, PS, PM, PL, and input ranges are respectively: -6, -4, -6, -2, -4,0, -2, 0,4, -2, 6, 4,6, membership function selects a trapezoidal distribution or triangle;
the linguistic variables of the output compressor frequency variation are: NL, NM, NS, Z, PS, PM, PL the increase of the compressor frequency is from negative to positive, the positive is a rapid increase of the frequency, the negative is a rapid decrease of the frequency, and the normalized domain range is [ -1, 1]Scale factorK u Set to 0.01.
Preferably, the fuzzy rule adopts an if-then fuzzy reasoning method, and the fuzzy rule table is shown in table 1:
TABLE 1 fuzzy rule TABLE
Weights OW [ i ] output in Table 1]Taking the intermediate value of each fuzzy set, performing defuzzification by adopting a weighted average method, and adopting a calculation formula as follows:，FS i to output membership of fuzzy sets.
The beneficial effects of the application are as follows: the application provides a control system of a heat pump drying system for preserved fruits, wherein the heat pump drying system can adjust the working frequency of a compressor and the working frequency of a fan by adopting a frequency converter so as to adjust the flow of a refrigerant and the drying air quantity, thereby realizing the adjustment according to the requirement.
Because the heat pump drying chamber is a nonlinear time-varying system, and a model is difficult to build by using a differential equation of a traditional physical system, the control system provided by the application adopts a fuzzy principle-based mode to adjust the frequency of the compressor, adjust the opening of the second expansion stop valve and the opening of the first expansion stop valve, adopts PID proportion control to adjust the opening of the moisture discharging port, and designs a fuzzy rule table based on a negative feedback principle and expert experience. The intelligent control strategy and the Internet of things technology are adopted to solve the problems of low control precision, poor disturbance resistance, low informatization and the like in the existing heat pump drying system, the automation and intelligent level is improved, and the main indexes of energy conservation, product quality improvement, high efficiency and reliability of the system are realized.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. Like elements or portions are generally identified by like reference numerals throughout the several figures. In the drawings, elements or portions thereof are not necessarily drawn to scale.
FIG. 1 is a schematic diagram of a heat pump drying system of the present application;
FIG. 2 is a schematic diagram of a control system of the present application;
fig. 3 is a view of a cloud platform MQTT architecture diagram of the present application.
FIG. 4 is a schematic diagram of the fuzzy control of the present application;
FIG. 5 is a trapezoidal membership function of error values for temperature;
FIG. 6 is a triangle membership function of error values for temperature;
FIG. 7 is a triangular membership function of output compressor frequency.
Description of the embodiments
The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
It should be understood that the terms "comprises" and "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.
As shown in fig. 1, the embodiment of the application provides a heat pump drying system for preserved fruits, which comprises a heat pump subsystem, a drying chamber 1 and a frequency converter, wherein the heat pump subsystem comprises a first heat exchanger 13, a first expansion stop valve 11, a second expansion stop valve 14, a four-way reversing valve 10, a second heat exchanger 2 and a compressor 9;
the second heat exchanger 2 is arranged at the top of the drying chamber 1, and the first heat exchanger 13, the first expansion stop valve 11, the second expansion stop valve 14 and the second heat exchanger 2 are connected in sequence; the four-way reversing valve 10 is respectively connected with the second heat exchanger 2, the compressor 9 and the first heat exchanger 13;
the top of the drying chamber 1 is also provided with a fan 3 and an electric heater 4, the upper part of the drying chamber 1 is provided with a moisture discharge port 8, the lower part of the drying chamber 1 is provided with a drying material rack 6, the lower part of the drying material rack 6 is provided with a weight sensor 7, and the drying chamber 1 is also provided with a humidity sensor 5 and a temperature sensor 12;
the compressor 9 and the fan 3 are respectively connected with a frequency converter, and the frequency converter is used for adjusting the working frequency of the compressor and the working frequency of the fan so as to adjust the flow of the refrigerant and the dry air quantity;
the working modes of the heat pump subsystem comprise a heating mode and a refrigerating mode, when the heat pump subsystem works in the heating mode, the second heat exchanger 2 is a condenser, and the first heat exchanger 13 is an evaporator; when operating in the cooling mode, the second heat exchanger 2 is an evaporator and the first heat exchanger 13 is a condenser. The inside of the drying chamber 1 forms a closed circulation system, the heating mode makes the temperature of the drying chamber 1 rise, at this time, the second heat exchanger 2 is a condenser, the first heat exchanger 13 is an evaporator, the expansion valve of the second expansion stop valve 14 at the outlet of the condenser stops working, the stop valve connected in parallel with the second expansion stop valve is conducted and flows through the refrigerating medium, the expansion valve of the first expansion stop valve 11 at the inlet of the evaporator works, and the stop valve connected in parallel with the first expansion stop valve is cut off and conducted. In contrast, in the cooling mode, the temperature of the drying chamber 1 is lowered, at this time, the second heat exchanger 2 is an evaporator, the first heat exchanger 13 is a condenser, the expansion valve of the first expansion stop valve 11 at the outlet of the condenser is stopped, the stop valve connected in parallel with the second heat exchanger is turned on, the refrigerant flows through the expansion valve of the second expansion stop valve 14 at the inlet of the evaporator is operated, and the stop valve connected in parallel with the second heat exchanger is turned off.
As shown in fig. 2, the specific embodiment of the application also provides a control system of the heat pump drying system for preserved fruits, which is applied to the heat pump drying system and comprises a PLC controller, a data acquisition module, a human-machine interface HMI and a cloud platform;
the data acquisition module is connected with the humidity sensor 5, the temperature sensor 12, the weight sensor 7 and the heat pump subsystem of the heat pump drying system, and is used for acquiring the operation condition data of the heat pump subsystem, the temperature and humidity in the drying chamber and the weight of the drying material rack 6, and transmitting the acquired data to the PLC; the PLC is respectively connected with the frequency converter, the first expansion stop valve 11, the second expansion stop valve 14 and the moisture discharge port actuator, the moisture discharge port actuator is connected with the moisture discharge port 8, and the PLC is used for controlling the opening of the moisture discharge port 8 according to an expert database, fuzzy rules and PID control rules, and controlling the opening of the first expansion stop valve 11 and the second expansion stop valve 14 so as to regulate the flow of the refrigerant and control the frequency of the frequency converter;
the human-machine interface HMI is connected with the PLC and used for carrying out human-machine interaction;
the cloud platform is connected with the PLC and the human-machine interface HMI respectively and is used for monitoring the operation condition of the heat pump drying system and storing monitoring data.
As shown in fig. 3, the cloud platform comprises an MQTT message proxy server and a database server, wherein the human-machine interface HMI is connected with the MQTT message proxy server and issues equipment running state and fault information to the client through an MQTT protocol; the database server is used for storing data and providing data services.
The MQTT message proxy server adopts an Ali cloud MQTT server, after the human-machine interface HMI is connected with the Ali cloud MQTT server, information such as equipment operation, state, faults and the like is published to the cloud platform through an MQTT protocol, clients such as mobile phone APP and Web subscribe related operation data information, and when the operation data changes, the clients receive the data sent by the MQTT server. Compared with a traditional client-server response communication mode, the MQTT communication mode reduces the burden of a server and saves communication flow, and has excellent performance when the cloud platform performs group control on a plurality of dryer devices.
The PLC controller controls the operation condition of the heat pump drying system according to an expert database, and the expert database stores the temperature and humidity of preserved fruit drying, the water content of materials, the drying time, the energy efficiency of the system and the superheat degree of the compressor 9, the fan 3, the first heat exchanger 13 or the second heat exchanger 2.
The PLC adjusts the frequency of the frequency converter and the opening degrees of the first expansion stop valve 11 and the second expansion stop valve 14 according to the fuzzy rule, when the frequency of the frequency converter is adjusted, the input variable is the temperature error value between the temperature in the drying chamber 1 and the set temperature, and the output value is the frequency of the frequency converter;
when the opening degrees of the first expansion shutoff valve 11 and the second expansion shutoff valve 14 are adjusted, the input amount is an error between the degree of superheat of the first heat exchanger 13 or the second heat exchanger 2 and the set degree of superheat, and the output is the opening degrees of the first expansion shutoff valve 11 and the second expansion shutoff valve 14.
As shown in fig. 4, in the fuzzy rule that the PLC controller adjusts the frequency of the inverter, the input variable is an error value of the set temperature, and the output variable is a variation of the compressor frequency. The language variable is expressed as: negative big, negative medium, negative small, zero, positive small, median, positive big, respectively denoted as NL, NM, NS, Z, PS, PM, PL; within the range of the argument [ -6 6], the input ranges are respectively: the membership functions of the [ -6, -4], [ -6, -2], [ -4,0], [ -2,2], [0,4], [2,6], [4,6] select a trapezoid distribution shape or a triangle, and the membership of the input value to each fuzzy variable is calculated through the membership functions as shown in fig. 5 and 6 respectively.
The input temperature is x, and the membership degree of the fuzzy set can be calculated by the following C language function, wherein a, b, C, d is the range of the universe of the fuzzy set, and b and C are equal when the membership function is a triangle:
float fuzzy_dmf (float x,a,b,c,d )
{ float dmf;
if(x>a&&x<b) {dmf = (x-a)/(b-a);}
else if(x>c&&x<d) {dmf=(d-x)/(d-c);}
else if(x<=b&&x<=c) {dmf=1}
else{dmf=0;}
return dmf ;
}
the linguistic variables of the output compressor frequency variation are: NL, NM, NS, Z, PS, PM, PL the increase of the compressor frequency is from negative to positive, the positive is a rapid increase of the frequency, the negative is a rapid decrease of the frequency, and the normalized domain range is [ -1, 1]Scale factorK u Set to 0.01, the membership function is shown in fig. 7.
The fuzzy rule is designed by expert experience knowledge and adopts an if-then fuzzy reasoning method, the error is large, the control quantity should be increased, the error is in direct proportion to the control quantity, the fuzzy rule table is shown in table 1, and the design of the fuzzy rule table is generally designed based on the negative feedback principle and expert experience.
TABLE 1 fuzzy rule TABLE
The weight OW [ i ] output in the table 1 takes the intermediate value of each fuzzy set, and the output fuzzy variable value obtained based on fuzzy reasoning is clarified by adopting a weighted average method, wherein the calculation formula is as follows:
，FS i to output membership of fuzzy sets.
The fuzzy rule table is expressed as follows by the structural variables in the C language, and is initialized according to the fuzzy rule table:
struct fuzzy_rule
{ float input 1;// input membership
float output1;// fuzzy output value
float f,// fuzzy rule weight
}struct fuzzy_rule R[7]。
After defuzzification, the compressor frequency is outputfThe calculation formula is as follows:
f=f_old+ output/K u ，f_oldinitialized to 50Hz, K u The quantization scale value is output for blurring.
The expansion valve flow control system adopts fuzzy logic control, and controls the refrigerant flow of the evaporator through the opening degree of the electronic expansion valve, so that the superheat degree of the evaporator is optimal, the refrigerant is fully provided for the evaporator, and the stable operation of the system is ensured. The input of the fuzzy control is the superheat error, and the output is the opening of the expansion valve. The design of the fuzzy rule table is generally designed based on the negative feedback principle and expert experience, and the design method is the same as described above.
The PLC controller adopts PID control rule to control the moisture discharging port actuator, and then adjusts the opening degree of the moisture discharging port 8, specifically inputs the error value between the set humidity of the drying chamber 1 and the actual humidity measured by the humidity sensor 5 into the PLC controller, and outputs the opening degree of the moisture discharging port 8 to adjust the humidity of the drying chamber 1.
Those of ordinary skill in the art will appreciate that the elements of the examples described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the elements of the examples have been described generally in terms of functionality in the foregoing description to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
In the embodiments provided in the present application, it should be understood that the division of the units is merely a logic function division, and there may be other division manners in actual implementation, for example, multiple units may be combined into one unit, one unit may be split into multiple units, or some features may be omitted.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the application, and are intended to be included within the scope of the appended claims and description.
Claims (3)
1. The control system for the heat pump drying system of the preserved fruit comprises a heat pump subsystem, a drying chamber (1) and a frequency converter, wherein the heat pump subsystem comprises a first heat exchanger (13), a first expansion stop valve (11), a second expansion stop valve (14), a four-way reversing valve (10), a second heat exchanger (2) and a compressor (9);
the second heat exchanger (2) is arranged at the top of the drying chamber (1), and the first heat exchanger (13), the first expansion stop valve (11), the second expansion stop valve (14) and the second heat exchanger (2) are connected in sequence; the four-way reversing valve (10) is respectively connected with the second heat exchanger (2), the compressor (9) and the first heat exchanger (13);
the top of the drying chamber (1) is also provided with a fan (3) and an electric heater (4), the upper part of the drying chamber (1) is provided with a moisture discharge port (8), the lower part of the drying chamber is provided with a drying material rack (6), the lower part of the drying material rack (6) is provided with a weight sensor (7), and the drying chamber (1) is also provided with a humidity sensor (5) and a temperature sensor (12);
the compressor (9) and the fan (3) are respectively connected with a frequency converter, and the frequency converter is used for adjusting the working frequency of the compressor and the working frequency of the fan so as to adjust the flow rate of the refrigerant and the dry air quantity;
the working modes of the heat pump subsystem comprise a heating mode and a refrigerating mode, when the heat pump subsystem works in the heating mode, the second heat exchanger (2) is a condenser, and the first heat exchanger (13) is an evaporator; when the air conditioner works in a refrigeration mode, the second heat exchanger (2) is an evaporator, and the first heat exchanger (13) is a condenser; the control system is characterized by comprising a PLC controller, a data acquisition module, a human-machine interface HMI and a cloud platform;
the data acquisition module is connected with a humidity sensor (5) and a temperature sensor (12) of the heat pump drying system, a weight sensor (7) and the heat pump subsystem, and is used for acquiring operation condition data of the heat pump subsystem, temperature and humidity in the drying chamber and weight of the drying material rack (6) and transmitting the acquired data to the PLC; the PLC is respectively connected with the frequency converter, the first expansion stop valve (11), the second expansion stop valve (14) and the moisture discharge port actuator, and the moisture discharge port actuator is connected with the moisture discharge port (8);
the human-machine interface HMI is connected with the PLC and used for carrying out human-machine interaction;
the cloud platform is connected with the human-machine interface HMI and is used for monitoring the operation condition of the heat pump drying system and storing monitoring data;
the PLC controls the operation condition of the heat pump drying system according to an expert database, wherein the expert database stores the temperature and humidity of preserved fruit drying, the water content of materials, the drying time, the energy efficiency of the system and the superheat degree of a compressor (9), a fan (3), a first heat exchanger (13) or a second heat exchanger (2);
the PLC adjusts the frequency of the frequency converter and the opening of the first expansion stop valve (11) and the second expansion stop valve (14) according to a fuzzy rule, when the frequency of the frequency converter is adjusted, the input variable is a temperature error value between the temperature in the drying chamber (1) and the set temperature, and the output value is the frequency of the frequency converter;
when the opening degree of the first expansion stop valve (11) and the second expansion stop valve (14) is regulated, the input quantity is the error between the superheat degree of the first heat exchanger (13) or the second heat exchanger (2) and the set superheat degree, and the output quantity is the opening degree of the first expansion stop valve (11) and the second expansion stop valve (14);
the PLC controller adopts PID control rules to control the moisture discharging port actuator, so as to adjust the opening of the moisture discharging port (8), specifically, an error value between the set humidity of the drying chamber (1) and the actual humidity measured by the humidity sensor (5) is input into the PLC controller, and the opening of the moisture discharging port (8) is output to adjust the humidity of the drying chamber (1);
the cloud platform comprises an MQTT message proxy server and a database server, wherein the human-machine interface HMI is connected with the MQTT message proxy server and distributes equipment running state and fault information to the client through an MQTT protocol; the database server is used for storing data and providing data services.
2. The control system of a heat pump drying system for preserved fruit according to claim 1, wherein in the fuzzy rule that the PLC controller adjusts the frequency of the frequency converter, the input variable is a temperature error value between the temperature in the drying chamber (1) and the set temperature, and the language variable is expressed as: negative big, negative medium, negative small, zero, positive small, medium and positive big, respectively denoted as NL, NM, NS, Z, PS, PM, PL, and input ranges are respectively: -6, -4, -6, -2, -4,0, -2, 0,4, -2, 6, 4,6, membership function selects a trapezoidal distribution or triangle;
the linguistic variables of the output compressor frequency variation are: NL, NM, NS, Z, PS, PM, PL the increase of the compressor frequency is from negative to positive, the positive is a rapid increase of the frequency, the negative is a rapid decrease of the frequency, and the normalized domain range is [ -1, 1]Scale factorK u Set to 0.01.
3. The control system for a heat pump drying system for preserved fruit according to claim 2, wherein the fuzzy rule adopts if-then fuzzy inference method, and the weight OW [ i ] is outputted]Taking the intermediate value of each fuzzy set, performing defuzzification by adopting a weighted average method, and adopting a calculation formula as follows:，FS i to output membership of fuzzy sets.
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| CN103175382A (en) * | 2011-12-26 | 2013-06-26 | 中国科学院理化技术研究所 | Heat pump drying system |
| CN104904894A (en) * | 2015-06-30 | 2015-09-16 | 四川中测量仪科技有限公司 | Tea leaf aroma improving machine and tea leaf intelligent control aroma improving pattern |
| CN109632304A (en) * | 2018-12-25 | 2019-04-16 | 哈尔滨工业大学 | Four-point contact ball running in machine and control method |
| CN111365977A (en) * | 2020-03-23 | 2020-07-03 | 顺德职业技术学院 | Control method of closed type variable frequency heat pump drying equipment |
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| US20150153078A1 (en) * | 2013-12-02 | 2015-06-04 | Hyundai Motor Company | Heat pump system for vehicle |
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| CN1737456A (en) * | 2004-08-17 | 2006-02-22 | Lg电子株式会社 | Electricity generating and air conditioning system with dehumidifier |
| CN103175382A (en) * | 2011-12-26 | 2013-06-26 | 中国科学院理化技术研究所 | Heat pump drying system |
| CN104904894A (en) * | 2015-06-30 | 2015-09-16 | 四川中测量仪科技有限公司 | Tea leaf aroma improving machine and tea leaf intelligent control aroma improving pattern |
| CN109632304A (en) * | 2018-12-25 | 2019-04-16 | 哈尔滨工业大学 | Four-point contact ball running in machine and control method |
| CN111365977A (en) * | 2020-03-23 | 2020-07-03 | 顺德职业技术学院 | Control method of closed type variable frequency heat pump drying equipment |
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