Drying chamber characteristic and heat pump drying system dynamic modeling method based on Modelica

Abstract

The invention discloses a drying chamber characteristic and heat pump drying system dynamic modeling method based on Modelica. The method comprises the steps that connectors of different physical domains in a heat pump drying system are designed; splitting the system into component model libraries according to different functions, and performing physical modeling respectively; adding a defined connector in the component model, and constructing a drying loop and a heat pump loop according to a system structure; the unstable drying characteristic of the drying chamber in the drying loop is explored, and a safe operation boundary is provided for the heat pump loop; designing parameters of key components of a heat pump loop and designing a PID controller; and carrying out simulation research to obtain dynamic response of the key parameters. According to the method, a physical model library of each component of the heat pump drying system is established, and a dynamic simulation model of the heat pump drying system is established on the basis; and the unstable drying characteristic of the drying chamber is disclosed, heat pump loop parameter design and PID control design are carried out, and the dynamic response performance of the system under closed-loop response is obtained through a step response experiment.

Description

Technical Field

[0001] The invention belongs to the field of heat pump drying system simulation, and in particular relates to a drying chamber characteristic and a heat pump drying system dynamic modeling method based on Modelica. Background Art

[0002] Heat pump drying uses heat pump technology to efficiently transfer environmental heat energy to dry grains, significantly reducing energy consumption compared to traditional methods. Originated from heat pump air conditioning technology, it achieves energy transfer through cyclic compression and expansion of working fluids, improves energy utilization efficiency, reduces environmental impact, and has become an important development direction of modern grain drying technology.

[0003] In response to the waste of waste heat at the outlet of the drying chamber, the patent (patent number: 202411001331.7) proposes a new type of heat pump drying system, which uses a regenerator and an evaporator to recover the waste heat of the warm and humid air at the outlet of the drying chamber in two stages. Although this can effectively recover heat, the unstable drying characteristics of the drying chamber cause the entire system to be in an open-loop unstable state. At the same time, due to the use of fresh air and changes in the external environment during the operation of the system, the entire integrated system is frequently in variable operating conditions, and there is a serious phenomenon of heat and moisture coupling, and the dynamic characteristics of the entire system are unclear. Therefore, in order to understand the operating characteristics of the new heat pump drying system in the dynamic process, and thus design an efficient and economical controller, a high-precision, easy-to-expand and transplant numerical simulation model is required.

[0004] For the new heat pump drying system, which is a strongly coupled system, the traditional modeling methods have common shortcomings in dealing with strongly coupled systems, such as high model complexity, difficulty in accurately capturing coupling effects, difficulty in cross-disciplinary integration, low simulation efficiency, and poor model reusability and scalability. These problems make the traditional methods inflexible and inefficient when dealing with complex dynamic systems. Summary of the invention

[0005] Purpose of the invention: The purpose of the invention is to provide a method for modeling the characteristics of a drying chamber and a heat pump drying system based on Modelica, which is convenient for studying the dynamic characteristics of a drying chamber and a new heat pump drying system, and provides a reference for system manufacturing and controller design.

[0006] Technical solution: A method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica of the present invention comprises the following steps:

[0007] S1: Determine the physical fields involved in the dynamic simulation model of the new heat pump drying system, and design the connector model under each physical field;

[0008] S2: Modular modeling of the new heat pump drying system is carried out according to different functions, and it is split into different component model libraries, including compressor model, expansion valve model, evaporator model, condenser model, drying chamber model, regenerator model and fan model;

[0009] S3: Place the connector model defined in S1 into the model in the component model library established in S2 through graphical modeling; and connect the connectors of different components to each other according to the system structure to form a dynamic simulation model of the heat pump circuit and the drying circuit;

[0010] S4: Study the dynamic process of heat and moisture coupling in the drying circuit, reveal the unstable drying characteristics of the drying chamber, determine the output of the heat and moisture characteristics of the drying chamber during the entire drying process, and provide safety boundary conditions for the safe operation of the heat pump circuit during the entire drying process;

[0011] S5: Based on the dynamic models of the drying circuit and the heat pump circuit, a dynamic simulation model of the entire heat pump drying system is constructed. According to the safety boundary conditions provided in S4, the operating parameters of the key equipment in the heat pump circuit are adjusted, including the volume and speed of the compressor, the flow area of ​​the expansion valve, and the heat exchange structure parameters of the condenser and evaporator. The PID controller is designed to clarify the control object and the controlled quantity, overcome the impact of the unstable characteristics of the drying chamber on the entire coupling system, and ensure the drying quality and safe operation of the system.

[0012] S6: Conduct dynamic simulation research, and obtain the closed-loop dynamic response characteristics of key parameters of the new heat pump drying system by performing step change experiments on the fresh air mass flow rate. Analyze the causes of the dynamic characteristics and provide a reference for the design of the system and new controller.

[0013] Furthermore, step 1 is specifically as follows: design connectors of different physical domains in the heat pump drying system, and define the logistics type, circulation variables, potential variables and flow variables in each connector; wherein the connector types include two-phase flow and humid air, the circulation variables are used to represent energy; the difference of potential variables is used to represent temperature and pressure; and the flow variables are used to describe enthalpy or components.

[0014] Furthermore, step 2 specifically includes the following steps:

[0015] S21: Dynamic modeling of heat pump circuit;

[0016] S211: Compressor Dynamic Modeling:

[0017] Since the compressor is fast in the dynamic response process, the operation process of the compressor is considered as a transient process, and the exhaust flow rate of the compressor is:

[0018]

[0019] Where η v is the volumetric efficiency of the compressor; ρ s is the suction density, kg / m 3 ; V c is the exhaust volume, m 3 / rad; N c is the rotation speed, rad / s;

[0020] The power consumption of the compressor is:

[0021]

[0022] Where, h″ is the outlet specific enthalpy of the isentropic compression process, kJ / kg; h′ is the suction specific enthalpy, kJ / kg; η s is the isentropic efficiency of the compressor;

[0023] The actual specific enthalpy at the compressor outlet is:

[0024]

[0025] S212: Condenser and Evaporator:

[0026] Both the condenser and the evaporator are fin-tube heat exchangers. The condensation process of the refrigerant in the condenser consists of a superheated zone, a two-phase zone, and a subcooled zone. The evaporation process in the evaporator consists of a two-phase zone and a superheated zone. For each zone in the condenser and the evaporator, the dynamic conservation equations of mass, pressure, and energy on the refrigerant side are shown in Equation (4);

[0027]

[0028] In the formula, q mr is the mass flow rate of refrigerant, kg / s; ξ r is the Lewis number of the refrigerant; the subscripts in and out represent the inlet and outlet; p r is the pressure of the refrigerant, kPa;

[0029] The mass, pressure and energy conservation equations on the moist air side of each region are shown in equation (5);

[0030]

[0031] In the formula, q ma,c is the mass flow rate of wet air condensation, kg / s; p a is the pressure of moist air, kPa;

[0032] In the heat transfer process on the wet air side, the wet air will form a layer of water film on the metal wall surface. The mass and energy conservation equations of the water film are shown in Equation (6);

[0033]

[0034] S213: Dynamic modeling of expansion valve:

[0035] The throttling process of the expansion valve is relatively fast and is considered as a transient process. It is regarded as an adiabatic isenthalpic process. The relationship between the enthalpy values ​​of the refrigerant on both sides of the expansion valve is:

[0036]

[0037] In the formula, and are the specific enthalpies of the expansion valve inlet and outlet, kJ / kg, respectively;

[0038] S22: Dynamic modeling of drying circuit;

[0039] S221: Based on the micro-element of the drying chamber, a dynamic model of thin layer drying is established, including the drying rate equation, component conservation equation, mass conservation equation, energy conservation equation and heat transfer rate equation. The micro-element is then iteratively solved to obtain the dynamic simulation model of the entire drying chamber:

[0040]

[0041] Where, M is the moisture content of grain; K is the drying rate coefficient; M e Balance grain moisture content for drying;

[0042]

[0043] In the formula, H in and H out is the moisture content of the inlet and outlet of the micro-element wet air in the drying chamber; x in and x out is the mass fraction of water vapor at the inlet and outlet of the drying chamber microelement wet air; ρ g is the dry microelement grain density, kg / m 3 ; A is the contact area between wet air and grain, m 2 ; ΔL is the dry microelement thickness, m; m in is the mass flow rate of wet air at the inlet of the dry microelement, kg / s;

[0044]

[0045] Where M0 is the initial moisture content of grain; out is the wet air mass flow rate at the outlet of the dry microelement, kg / s;

[0046]

[0047] In the formula, h cv is the heat transfer coefficient between grain and moist air, kW / (m2 .℃); c w is the specific heat capacity of water vapor at constant pressure, kJ / (kg.℃); c a is the constant pressure specific heat capacity of dry air, kJ / (kg.℃); T in and T out T is the inlet and outlet temperature of the dry micro-element wet air, °C; g is the grain temperature, °C;

[0048]

[0049] In the formula, c g is the specific heat capacity of grain at constant pressure, kJ / (kg.K); c l is the specific heat capacity of water at constant pressure, kJ / (kg.K); L a is the latent heat of vaporization, kJ / kg;

[0050] S222: Regenerator Dynamic Modeling:

[0051] The regenerator uses a plate heat exchanger. During the dynamic response of the regenerator, the mass conservation equation, pressure drop equation and energy conservation equation of the wet air and water film on the metal wall surface on both sides are based on formulas (5) and (6);

[0052] S223: Fan Dynamic Modeling:

[0053] The operation process of the fan is also considered as a transient process, and the power consumption of the fan is:

[0054]

[0055] Where V a is the fresh air volume flow rate, m 3 / s;p a is the fresh air pressure, kPa; η f is the fan efficiency.

[0056] Furthermore, step 3 is specifically as follows: add a two-phase flow inlet connector and a two-phase flow outlet connector to the compressor model; add a two-phase flow inlet connector and a two-phase flow outlet connector to the expansion valve model; add a two-phase flow inlet connector, a two-phase flow outlet connector, a wet air inlet connector, and a wet air outlet connector to the evaporator and condenser models; place a wet air inlet connector and a wet air outlet connector in the fan model; place a wet air inlet connector and a wet air outlet connector in the drying chamber model; place two wet air inlet connectors and two wet air outlet connectors in the regenerator model; wherein the fan inlet connector is connected to the atmospheric environment, and the fan outlet is connected to the The connector is connected to the wet air inlet connector of the condenser, the wet air outlet connector of the condenser is connected to the drying chamber inlet connector, the drying chamber outlet connector is connected to the first wet air inlet connector of the regenerator, the first wet air outlet connector of the regenerator is connected to the wet air inlet connector of the evaporator, and the wet air outlet connector of the evaporator leads to the external environment to form a drying circuit; the two-phase flow outlet connector of the compressor is connected to the two-phase flow inlet connector of the condenser, the two-phase flow outlet connector of the condenser is connected to the two-phase flow inlet connector of the expansion valve, the two-phase flow outlet connector of the expansion valve is connected to the two-phase flow inlet connector of the evaporator, and the two-phase flow outlet connector of the evaporator is connected to the two-phase flow inlet connector of the compressor to form a heat pump circuit.

[0057] Furthermore, step 4 is specifically as follows: setting the fresh air volume to 0.5 kg / s, setting the ambient temperature to 20°C, setting the ambient relative humidity to 70%, setting the drying temperature to 55°C, the initial moisture content of the grain to 0.3, the target moisture content to 0.14, the initial mass to 100 kg, and the length, width and height of the drying chamber to 0.4 m, 0.4 m and 1.1 m respectively; when the rated grain moisture content target is reached, the temperature of the wet air at the outlet of the drying chamber varies from 37.6°C to 50.3°C, and the relative humidity varies from 72% to 56%, providing safety boundary conditions for the subsequent heat pump loop parameter design and PID control design.

[0058] Furthermore, step 5 specifically includes the following steps:

[0059] S51: Based on the dynamic models of the drying circuit and the heat pump circuit, a dynamic simulation model of the entire heat pump drying system is constructed;

[0060] S52: Based on the operating range of the temperature and relative humidity of the wet air at the drying chamber outlet provided in S4, open-loop simulation operation is performed by adjusting the operating parameters of each key device in the heat pump circuit, including the volume and speed of the compressor, the flow area of ​​the expansion valve, and the heat exchange structure parameters of the condenser and the evaporator; since the drying chamber outlet temperature is the lowest and the waste heat recovery effect is the worst at the initial stage of drying, the heat pump circuit needs to be debugged at the initial stage of drying to meet the system operating conditions under this extreme condition, including the drying temperature and superheat. When the drying temperature is lower than the set value, the volume and speed of the compressor and the heat exchange area of ​​the condenser are increased; when the drying temperature exceeds the set value, the opposite is performed. Operation, so that the drying temperature is near the set value at the initial stage of drying; when the superheat is lower than the set value, the flow area of ​​the expansion valve and the heat exchange area of ​​the evaporator are increased, and when the superheat exceeds the set value, the opposite operation is performed to make the superheat near the set value at the initial stage of drying; in addition, due to the integrated coupling characteristics of the system, there is a serious coupling between the drying temperature and the superheat, the two are positively correlated and affect each other; therefore, in the process of parameter debugging, the debugging range can be reduced to avoid overshoot; based on the above debugging results, the volume parameters of the compressor, the heat exchange structure parameters of the evaporator and condenser, and the initial values ​​of the compressor speed and the expansion valve opening are provided for the subsequent design of the PID controller;

[0061] S53: Design a PID controller, set the controlled variable y to the drying temperature y1 and the superheat y2, the drying temperature y1 is set to 55°C, the superheat y2 is set to 5°C, and the control object u is set to the expansion valve opening u1 and the compressor speed u2; according to the different control objects, two control schemes are obtained: Scheme 1, expansion valve opening u1 and compressor speed u2, the expansion valve opening is used to control the drying temperature, and the compressor speed is used to control the superheat; Scheme 2, compressor speed u1 and expansion valve opening u2, the compressor speed is used to control the drying temperature, and the expansion valve opening is used to control the superheat; Based on the structural parameters of the compressor, condenser and evaporator provided in S52, as well as the initial values ​​of the compressor speed and the expansion valve opening, debug the parameter K in the PID controller in the two control schemes p , K i and K d , and compare and analyze the feasibility and superiority of the two control schemes.

[0062] Furthermore, step 6 specifically includes the following steps:

[0063] S61: Set the initial fresh air mass flow rate to 0.5kg / s, increase it to 0.55kg / s at 7000s, and then decrease it to 0.45kg / s at 10000s. Adjust the step process of the fresh air mass flow rate. Under this step condition, adjust the dynamic response process of the humid air heat absorption in the condenser, the compressor and the fan power consumption. The fresh air mass flow rate increases stepwise, and the compressor power consumption, fan power consumption and humid air heat absorption all increase suddenly. The increase in fan power consumption is caused by the step increase in the fresh air flow rate, and its power consumption is positively correlated with the fresh air mass flow rate; the compressor power consumption is first ignored. It gradually increases after a slight decrease. This is because the compressor speed is used to control the superheat. The superheat has a step-up phenomenon at the beginning of the step, so the compressor speed is reduced at the initial stage; the heat absorption of wet air in the condenser shows a two-stage trend, first a step-up, then a slight decrease and then an increase. This is a step increase in the mass flow of fresh air. The heat exchange area is more fully utilized, and more heat is taken away instantly. The subsequent trend corresponds to the law of the compressor speed, which first decreases and then increases. When the mass flow of fresh air decreases in a step, the power consumption of the compressor, the power consumption of the fan and the heat absorption of wet air have opposite responses.

[0064] S62: Dynamic response process of adjusting drying temperature and superheat. The fresh air mass flow rate increases in steps. The heat released by the refrigerant in the condenser cannot meet the demand of wet air. The drying temperature drops sharply. The PID control intervenes to reduce the expansion valve opening and the outlet refrigerant pressure decreases. Therefore, the superheat will have an initial reverse phenomenon, showing a trend of first increasing in steps and then decreasing. Since the compressor speed is used to control the superheat, the compressor power consumption will also change accordingly, first slightly decreasing and then increasing. The fresh air mass flow rate decreases in steps. The heat released by the refrigerant in the condenser exceeds the demand of wet air. The drying temperature increases sharply. The PID control intervenes to increase the expansion valve opening and the outlet refrigerant pressure increases. Therefore, the superheat will first decrease in steps and then increase. In addition, since the superheat is affected by the expansion valve opening and the compressor speed at the same time, it is also affected by the expansion valve outlet refrigerant pressure and flow rate. Therefore, the sensitivity of the superheat under disturbance is much higher than that of the drying temperature. The step increase of the fresh air mass flow rate is the opposite.

[0065] S63: Adjust the dynamic response process of the heat pump coefficient of performance (COP) and dehumidification per unit energy consumption (SMER). The fresh air mass flow rate increases step by step. Since the amount of heat absorbed by the humid air increases step by step, and there is a response time for the increase in the compressor speed, the COP first increases step by step and then decreases, while the SMER decreases significantly. Although the increase in the fresh air mass will lead to an increase in the drying rate of the drying chamber to a certain extent, its increase rate is much smaller than the increase rate of the compressor power consumption and the fan power consumption, while the step decrease in the fresh air flow rate is the opposite. In addition, as the drying process proceeds, the COP gradually increases, while the SMER gradually decreases. This is because the temperature of the humid air at the outlet of the drying chamber continues to increase, the amount of waste heat recovered in the regenerator increases, the compressor power consumption increases and decreases, and the drying rate decreases at a rate much higher than the compressor power consumption decreases, so the SMER gradually decreases.

[0066] The present invention also discloses a computer device, comprising a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method of the present invention.

[0067] The present invention also discloses a computer-readable storage medium on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method of the present invention are implemented.

[0068] The present invention also discloses a computer program product, comprising a computer program / instruction, which implements the steps of the method of the present invention when executed by a processor.

[0069] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention discloses a method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica, and proposes a new heat pump drying model library including compressor model, expansion valve model, evaporator model, condenser model, drying chamber model, regenerator model and fan model; reveals the unstable drying characteristics of the drying chamber, and carries out heat pump loop parameter design and PID control design, overcoming the influence of the unstable characteristics of the drying chamber on the safe operation of the entire integrated system, and then through step response experiments, obtains the dynamic response curve of key parameters under closed-loop response, which is used for the design of advanced controllers. The modern modeling language Modelica can more effectively describe and simulate strongly coupled systems through its declarative and multi-physical domain integration capabilities, improve the maintainability and simulation efficiency of the model, and promote the progress of engineering design and optimization processes. It is suitable for new heat pump drying systems with strong coupling including multiple physical domains. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a structural schematic diagram of a dynamic model of a novel heat pump drying system in a specific embodiment of the present invention;

[0071] Figure 2 It is a graphical modeling interface of a new heat pump drying system based on Modelica in a specific implementation manner of the present invention;

[0072] Figure 3 This is a schematic diagram of the one-dimensional dynamic modeling idea of ​​the drying chamber;

[0073] Figure 4 It is a schematic diagram of the change of the wet air temperature at the outlet of the drying chamber at the rated drying temperature;

[0074] Figure 5 It is a schematic diagram of the changes in the relative humidity of the wet air at the drying chamber outlet and the moisture content of the grains at the rated drying temperature;

[0075] Figure 6 It is a step situation diagram of the fresh air mass flow rate in a specific implementation manner of the present invention;

[0076] Figure 7 It is a dynamic response diagram of the heat absorption of wet air in the condenser, the power consumption of the compressor and the fan when the fresh air mass flow rate undergoes a step change in a specific embodiment of the present invention;

[0077] Figure 8 It is a dynamic response diagram of the drying temperature when the fresh air mass flow rate undergoes a step change in a specific embodiment of the present invention;

[0078] Fig. 9 It is a dynamic response diagram of superheat when the fresh air mass flow rate undergoes a step change in a specific embodiment of the present invention;

[0079] Fig.10 It is a dynamic response diagram of the coefficient of performance (COP) of the heat pump when the fresh air mass flow rate undergoes a step change in a specific embodiment of the present invention;

[0080] Fig.11 It is a dynamic response diagram of the dehumidification capacity per unit energy consumption (SMER) when the fresh air mass flow rate undergoes a step change in a specific implementation manner of the present invention. DETAILED DESCRIPTION

[0081] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0082] This specific embodiment discloses a drying chamber characteristic and heat pump drying system dynamic modeling method based on Modelica, comprising the following steps:

[0083] S1: Clarify the physical fields involved in the dynamic simulation model of the new heat pump drying system, and design the connector model under each physical field.

[0084] S2: Modular modeling of the new heat pump drying system is carried out according to different functions, and it is split into a model library containing different components, including compressor model, expansion valve model, evaporator model, condenser model, drying chamber model, regenerator model and fan model;

[0085] S3: Place the connector defined in S1 into the model in the component model library established in S2 through graphical modeling; and connect the connectors of different components to each other according to the system structure to form a dynamic simulation model of the heat pump circuit and the drying circuit;

[0086] S4: Explore the dynamic process of thermal and moisture coupling in the drying circuit, reveal the unstable drying characteristics of the drying chamber, determine the output of the thermal and moisture characteristics of the drying chamber during the entire drying process, and provide safety boundary conditions for the safe operation of the heat pump circuit during the entire drying process;

[0087] S5: Based on the dynamic models of the drying circuit and the heat pump circuit, a dynamic simulation model of the entire heat pump drying system is constructed. According to the safety boundary conditions provided in S4, the operating parameters of the key equipment in the heat pump circuit are adjusted, including the volume and speed of the compressor, the flow area of ​​the expansion valve, the heat exchange structure parameters of the condenser and the evaporator, and other parameters. The PID controller is designed to clarify the control object and the controlled quantity, overcome the impact of the unstable characteristics of the drying chamber on the entire coupling system, and ensure the drying quality and safe operation of the system.

[0088] S6: Conduct dynamic simulation research, and obtain the closed-loop dynamic response characteristics of key parameters of the new heat pump drying system by performing step-change experiments on the fresh air mass flow rate. Analyze the causes of the dynamic characteristics and provide reference for the design of the system and new controller.

[0089] The dynamic simulation model of the new heat pump drying system in step S1 has two types of connectors, namely, a two-phase flow connector and a wet air connector, and each connector may have circulation variables, potential variables, and flow variables. Among them, the circulation variable in the two-phase flow connector is the mass flow rate of the refrigerant, the potential variable is the pressure, and the flow variable is the temperature and the mass fraction of the refrigerant; the circulation variable in the wet air connector is the mass flow rate of the wet air, the potential variable is the pressure, and the flow variable is the specific enthalpy and moisture content of the wet air; the circulation variable in the heat connector is the heat flow, and the potential variable is the temperature.

[0090] The modeling of each component in step S2 specifically includes the following steps:

[0091] S21: Dynamic modeling of heat pump circuit;

[0092] S211: Compressor Dynamic Modeling:

[0093] Since the compressor is fast in the dynamic response process, the operation process of the compressor is considered as a transient process, and the exhaust flow rate of the compressor is:

[0094]

[0095] Where η v is the volumetric efficiency of the compressor; ρ s is the suction density, kg / m 3 ; V c is the exhaust volume, m 3 / rad; N c is the rotation speed, rad / s;

[0096] The power consumption of the compressor is:

[0097]

[0098] Where, h″ is the outlet specific enthalpy of the isentropic compression process, kJ / kg; h′ is the suction specific enthalpy, kJ / kg; η s is the isentropic efficiency of the compressor;

[0099] The actual specific enthalpy at the compressor outlet is:

[0100]

[0101] S212: Condenser and Evaporator:

[0102] Both the condenser and the evaporator are fin-tube heat exchangers. The condensation process of the refrigerant in the condenser consists of a superheated zone, a two-phase zone, and a subcooled zone. The evaporation process in the evaporator consists of a two-phase zone and a superheated zone. For each zone in the condenser and the evaporator, the dynamic conservation equations of mass, pressure, and energy on the refrigerant side are shown in Equation (4);

[0103]

[0104] In the formula, q mr is the mass flow rate of refrigerant, kg / s; ξ r is the Lewis number of the refrigerant; the subscripts in and out represent the inlet and outlet; p r is the pressure of the refrigerant, kPa;

[0105] The mass, pressure and energy conservation equations on the moist air side of each region are shown in equation (5);

[0106]

[0107] In the formula, q ma,c is the mass flow rate of wet air condensation, kg / s; p a is the pressure of moist air, kPa;

[0108] In the heat transfer process on the wet air side, the wet air will form a layer of water film on the metal wall surface. The mass and energy conservation equations of the water film are shown in Equation (6);

[0109]

[0110] S213: Dynamic modeling of expansion valve:

[0111] The throttling process of the expansion valve is relatively fast and is considered as a transient process. It is regarded as an adiabatic isenthalpic process. The relationship between the enthalpy values ​​of the refrigerant on both sides of the expansion valve is:

[0112]

[0113] In the formula, and are the specific enthalpies of the expansion valve inlet and outlet, kJ / kg, respectively;

[0114] S22: Dynamic modeling of drying circuit;

[0115] S221: Based on the micro-element of the drying chamber, a dynamic model of thin layer drying is established, including the drying rate equation, component conservation equation, mass conservation equation, energy conservation equation and heat transfer rate equation. The micro-element is then iteratively solved to obtain the dynamic simulation model of the entire drying chamber:

[0116]

[0117] Where, M is the moisture content of grain; K is the drying rate coefficient; M e Balance grain moisture content for drying;

[0118]

[0119] In the formula, H in and H out is the moisture content of the inlet and outlet of the micro-element wet air in the drying chamber; x in and x out is the mass fraction of water vapor at the inlet and outlet of the drying chamber micro-element wet air; ρ g is the dry microelement grain density, kg / m 3 ; A is the contact area between wet air and grain, m 2 ; ΔL is the dry microelement thickness, m; m in is the mass flow rate of wet air at the inlet of the dry microelement, kg / s;

[0120]

[0121] Where M0 is the initial moisture content of grain; out is the wet air mass flow rate at the outlet of the dry microelement, kg / s;

[0122]

[0123] In the formula, h cv is the heat transfer coefficient between grain and moist air, kW / (m 2 .℃); c w is the specific heat capacity of water vapor at constant pressure, kJ / (kg.℃); c a is the constant pressure specific heat capacity of dry air, kJ / (kg.℃); T in and T out T is the inlet and outlet temperature of the dry micro-element wet air, °C; g is the grain temperature, °C;

[0124]

[0125] In the formula, c g is the specific heat capacity of grain at constant pressure, kJ / (kg.K); c l is the specific heat capacity of water at constant pressure, kJ / (kg.K); L a is the latent heat of vaporization, kJ / kg;

[0126] S222: Regenerator Dynamic Modeling:

[0127] The regenerator uses a plate heat exchanger. During the dynamic response of the regenerator, the mass conservation equation, pressure drop equation and energy conservation equation of the wet air and water film on the metal wall surface on both sides are based on formulas (5) and (6);

[0128] S223: Fan Dynamic Modeling:

[0129] The operation process of the fan is also considered as a transient process, and the power consumption of the fan is:

[0130]

[0131] Where V a is the fresh air volume flow rate, m 3 / s;p a is the fresh air pressure, kPa; η f is the fan efficiency.

[0132] In step S3, a two-phase flow inlet connector and a two-phase flow outlet connector are added to the compressor model; a two-phase flow inlet connector and a two-phase flow outlet connector are added to the expansion valve model; a two-phase flow inlet connector, a two-phase flow outlet connector, a wet air inlet connector, and a wet air outlet connector are added to the evaporator and condenser models; a wet air inlet connector and a wet air outlet connector are placed in the fan model; a wet air inlet connector and a wet air outlet connector are placed in the drying chamber model; two wet air inlet connectors and two wet air outlet connectors are placed in the regenerator model. The connection relationship between the connectors is as follows: Figure 2 As shown. Among them, the fan inlet connector is connected to the atmospheric environment, the fan outlet connector is connected to the wet air inlet connector of the condenser, the wet air outlet connector of the condenser is connected to the drying chamber inlet connector, the drying chamber outlet connector is connected to the first wet air inlet connector of the regenerator, the first wet air outlet connector of the regenerator is connected to the wet air inlet connector of the evaporator, and the wet air outlet connector of the evaporator leads to the external environment to form a drying circuit; the two-phase flow outlet connector of the compressor is connected to the two-phase flow inlet connector of the condenser, the two-phase flow outlet connector of the condenser is connected to the two-phase flow inlet connector of the expansion valve, the two-phase flow outlet connector of the expansion valve is connected to the two-phase flow inlet connector of the evaporator, and the two-phase flow outlet connector of the evaporator is connected to the two-phase flow inlet connector of the compressor to form a heat pump circuit.

[0133] In step S4, the fresh air volume is set to 0.5 kg / s, the ambient temperature is set to 20 ° C, the relative humidity is set to 70%, the drying temperature is set to 55 ° C, the initial moisture content of the grain is 0.3, the target moisture content is 0.14, the initial mass is 100 kg, and the length, width and height of the drying chamber are 0.4 m, 0.4 m and 1.1 m respectively. Based on these conditions, the dynamic process of thermal and humid coupling and the unstable drying characteristics of the drying chamber are explored. During the entire drying process, the temperature of the wet air at the outlet of the drying chamber is as follows: Figure 4 As shown, the relative humidity of the wet air at the drying chamber outlet and the moisture content of the grain are as follows Figure 5As shown. It can be found that as the drying process proceeds, the temperature at the outlet of the drying chamber gradually increases, the moisture content of the outlet wet air gradually decreases, and the moisture content of the grains gradually decreases. This is because as the drying process proceeds, the moisture content of the grains continues to decrease, while the relative humidity and moisture content of the wet air in the hot dry air remain unchanged. As the drying process proceeds, the moisture gradient difference between the hot dry air and the grains continues to decrease, and the dehumidification driving force gradually decreases. The ability of the hot dry air to take away moisture from the grains becomes weaker and weaker, and the sensible heat of the hot dry air is used less and less for the latent heat of the moisture in the grains. Therefore, the temperature of the hot dry air will gradually increase, and the amount of moisture in the grains transferred to the wet air will gradually decrease. Based on the above results, it can be seen that the temperature of the wet air at the outlet of the drying chamber continues to increase, and the moisture content continues to decrease, which is in an unstable state, resulting in the thermodynamic parameters of the inlet wet air of the regenerator and the evaporator are also in a continuous changing process, which ultimately causes the entire new heat pump drying system to be in an open-loop unstable state. Therefore, it is necessary to carry out full-condition design and PID control design of the parameters of the heat pump circuit. In addition, when the rated grain moisture content target is reached, the temperature of the wet air at the drying chamber outlet varies from 37.6℃ to 50.3℃, and the relative humidity varies from 72% to 56%, which can provide safety boundary conditions for the subsequent heat pump loop parameter design and PID control design.

[0134] Step S5 specifically includes the following steps:

[0135] S51: Based on the dynamic models of the drying circuit and the heat pump circuit, a dynamic simulation model of the entire heat pump drying system is constructed;

[0136] S52: Based on the operating range of the temperature and relative humidity of the wet air at the outlet of the drying chamber provided in S4, the operating parameters of each key device in the heat pump circuit, including the volume and speed of the compressor, the flow area of ​​the expansion valve, the heat exchange structure parameters of the condenser and the evaporator, are adjusted to perform open-loop simulation operation. Since the outlet temperature of the drying chamber is the lowest and the waste heat recovery effect is the worst at the initial stage of drying, the heat pump circuit needs to be debugged at the initial stage of drying to meet the system operating conditions (drying temperature and superheat) under this extreme condition. When the drying temperature is lower than the set value, the volume and speed of the compressor and the heat exchange area of ​​the condenser can be increased. When the drying temperature exceeds the set value, the opposite operation can be performed to try to make the drying temperature near the set value at the initial stage of drying, which is convenient for the subsequent PID controller design; when the superheat is lower than the set value, the flow area of ​​the expansion valve and the heat exchange area of ​​the evaporator can be increased. When the superheat exceeds the set value, the opposite operation can be performed to try to make the superheat near the set value at the initial stage of drying, which is convenient for the subsequent PID controller design. In addition, due to the integrated coupling characteristics of the system, the drying temperature and superheat are seriously coupled, and the two are positively correlated and affect each other. Therefore, during the parameter debugging process, the debugging amplitude can be reduced to avoid overshoot. Based on the above debugging results, the volume parameters of the compressor, the heat exchange structure parameters of the evaporator and condenser, and the initial values ​​of the compressor speed and expansion valve opening can be provided for the subsequent PID controller design.

[0137] S53: Carry out PID controller design, set the controlled quantity (y) to drying temperature (y1) and superheat (y2). The former is set to 55°C to ensure the drying quality, and the latter is set to 5°C to ensure the safe operation of the heat pump circuit. The control object (u) is set to the expansion valve opening and the compressor speed. According to the different control objects, two control schemes can be obtained: Scheme 1, expansion valve opening (u1) and compressor speed (u2), the expansion valve opening is used to control the drying temperature, and the compressor speed is used to control the superheat; Scheme 2, compressor speed (u1) and expansion valve opening (u2), the compressor speed is used to control the drying temperature, and the expansion valve opening is used to control the superheat. Based on the structural parameters of the compressor, condenser and evaporator provided in S52, as well as the initial values ​​of the compressor speed and the expansion valve opening, debug the parameter K in the PID controller in the two control schemes. p , K i and K d, and compared and analyzed the feasibility and superiority of the two control schemes. The results show that the control scheme 1 can realize the control of the drying temperature and superheat of the entire integrated system, but the control scheme 2 cannot realize the control of the drying temperature and superheat of the entire integrated system. Therefore, in the subsequent closed-loop response simulation, the expansion valve opening is used to control the drying temperature, and the compressor speed is used to control the superheat to overcome the impact of the unstable characteristics of the drying chamber on the entire coupling system, ensuring the drying quality and safe operation of the system.

[0138] Expansion valve opening (u1) and compressor speed (u2)

[0139] Step S6 specifically includes the following steps:

[0140] The initial fresh air mass flow rate is set to 0.5 kg / s, which is increased to 0.55 kg / s at 7000 s and then decreased to 0.45 kg / s at 10000 s. The step process of the fresh air mass flow rate is as follows: Figure 6 In this step case, the dynamic response process of the heat absorption of wet air in the condenser, the power consumption of the compressor and the fan is as follows Figure 7 As shown in the figure, the fresh air mass flow rate increases in a step, and the compressor power consumption, fan power consumption and humid air heat absorption all increase suddenly. The increase in fan power consumption is caused by the step increase in fresh air flow, and its power consumption is positively correlated with the fresh air mass flow rate; the compressor power consumption first decreases slightly and then gradually increases. This is because the compressor speed is used to control the superheat. The superheat has a step increase phenomenon at the beginning of the step, so the compressor speed is first reduced in the initial stage; the condenser humid air heat absorption shows a two-stage trend, first a step increase, then a slight decrease and then an increase. This is a step increase in the fresh air mass flow rate, and the heat exchange area is more fully utilized, which instantly takes away more heat. The subsequent period corresponds to the law of the compressor speed, which first decreases and then increases. When the fresh air mass flow rate decreases in a step, the compressor power consumption, fan power consumption and humid air heat absorption have opposite responses.

[0141] The dynamic response processes of drying temperature and superheat are as follows: Figure 8 and Fig. 9As shown, the fresh air mass flow rate increases in a step-up manner, the heat released by the refrigerant in the condenser cannot meet the demand of the wet air, the drying temperature drops sharply, the PID control intervenes, the expansion valve opening is reduced, and the outlet refrigerant pressure decreases, so the superheat will have an initial reverse phenomenon, showing a trend of first increasing in a step and then decreasing. Since the compressor speed is used to control the superheat, the compressor power consumption will also change accordingly, first slightly decreasing and then increasing; the fresh air mass flow rate decreases in a step-down manner, the refrigerant heat released in the condenser exceeds the demand of the wet air, the drying temperature increases sharply, the PID control intervenes, the expansion valve opening is increased, and the outlet refrigerant pressure increases, so the superheat will first decrease in a step and then increase. In addition, since the superheat is affected by both the expansion valve opening and the compressor speed, and is also affected by the expansion valve outlet refrigerant pressure and flow, it can be found that the sensitivity of the superheat under disturbance is much higher than the drying temperature. The step-up of the fresh air mass flow rate is the opposite.

[0142] The dynamic response process of COP and SMER is as follows Fig.10 and Fig.11 As shown, the fresh air mass flow rate increases in steps. Since the amount of heat absorbed by the humid air increases in steps, and there is a response time for the increase in the compressor speed, the COP first increases in steps and then decreases, while the SMER decreases significantly. Although the increase in the fresh air quality will lead to an increase in the drying rate of the drying chamber to a certain extent, its increase rate is much smaller than the increase rate of the compressor power consumption and the fan power consumption, while the step decrease in the fresh air flow rate is the opposite. In addition, it can be found that as the drying process proceeds, the COP gradually increases, while the SMER gradually decreases. This is because the temperature of the humid air at the outlet of the drying chamber has been increasing, the amount of waste heat recovered by the regenerator has increased, the compressor power consumption has increased and decreased, and the drying rate reduction rate is much higher than the compressor power consumption reduction rate, so the SMER gradually decreases.

Claims

1. A method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica, characterized in that: The steps include: S1: Determine the physical fields involved in the dynamic simulation model of the new heat pump drying system, and design the connector model under each physical field; S2: Modular modeling of the new heat pump drying system is carried out according to different functions, and it is split into different component model libraries, including compressor model, expansion valve model, evaporator model, condenser model, drying chamber model, regenerator model and fan model; S3: Place the connector model defined in S1 into the model in the component model library established in S2 through graphical modeling; and connect the connectors of different components to each other according to the system structure to form a dynamic simulation model of the heat pump circuit and the drying circuit; S4: Study the dynamic process of heat and moisture coupling in the drying circuit, reveal the unstable drying characteristics of the drying chamber, determine the output of the heat and moisture characteristics of the drying chamber during the entire drying process, and provide safety boundary conditions for the safe operation of the heat pump circuit during the entire drying process; S5: Based on the dynamic models of the drying circuit and the heat pump circuit, a dynamic simulation model of the entire heat pump drying system is constructed. According to the safety boundary conditions provided in S4, the operating parameters of the key equipment in the heat pump circuit are adjusted, including the volume and speed of the compressor, the flow area of ​​the expansion valve, and the heat exchange structure parameters of the condenser and evaporator. The PID controller is designed to clarify the control object and the controlled quantity, overcome the impact of the unstable characteristics of the drying chamber on the entire coupling system, and ensure the drying quality and safe operation of the system. S6: Conduct dynamic simulation research, and obtain the closed-loop dynamic response characteristics of key parameters of the new heat pump drying system by performing step change experiments on the fresh air mass flow rate. Analyze the causes of the dynamic characteristics and provide a reference for the design of the system and new controller.

2. The method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica according to claim 1, characterized in that: Step 1 is specifically as follows: design connectors for different physical domains in the heat pump drying system, and define the logistics type, circulation variables, potential variables, and flow variables in each connector; the connector types include two-phase flow and humid air, and the circulation variables are used to represent energy; the difference of potential variables is used to represent temperature and pressure; and the flow variables are used to describe enthalpy or components.

3. The method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica according to claim 1, characterized in that: Step 2 specifically includes the following steps: S21: Dynamic modeling of heat pump circuit; S211: Compressor Dynamic Modeling: Since the compressor is fast in the dynamic response process, the operation process of the compressor is considered as a transient process, and the exhaust flow rate of the compressor is: Where η v is the volumetric efficiency of the compressor; ρ s is the suction density, kg / m 3 ; V c is the exhaust volume, m 3 / rad; N c is the rotation speed, rad / s; The power consumption of the compressor is: Where, h″ is the outlet specific enthalpy of the isentropic compression process, kJ / kg; h′ is the suction specific enthalpy, kJ / kg; η s is the isentropic efficiency of the compressor; The actual specific enthalpy at the compressor outlet is: S212: Condenser and Evaporator: Both the condenser and the evaporator are fin-tube heat exchangers. The condensation process of the refrigerant in the condenser consists of a superheated zone, a two-phase zone, and a subcooled zone. The evaporation process in the evaporator consists of a two-phase zone and a superheated zone. For each zone in the condenser and the evaporator, the dynamic conservation equations of mass, pressure, and energy on the refrigerant side are shown in Equation (4); In the formula, q mr is the mass flow rate of refrigerant, kg / s; ξ r is the Lewis number of the refrigerant; the subscripts in and out represent the inlet and outlet; p r is the pressure of the refrigerant, kPa; The mass, pressure and energy conservation equations on the moist air side of each region are shown in equation (5); In the formula, q ma,c is the mass flow rate of wet air condensation, kg / s; p a is the pressure of moist air, kPa; In the heat transfer process on the wet air side, the wet air will form a layer of water film on the metal wall surface. The mass and energy conservation equations of the water film are shown in Equation (6); S213: Dynamic modeling of expansion valve: The throttling process of the expansion valve is relatively fast and is considered as a transient process. It is regarded as an adiabatic isenthalpic process. The relationship between the enthalpy values ​​of the refrigerant on both sides of the expansion valve is: In the formula, and are the specific enthalpies of the expansion valve inlet and outlet, kJ / kg; S22: Dynamic modeling of drying circuit; S221: Based on the micro-element of the drying chamber, a dynamic model of thin layer drying is established, including the drying rate equation, component conservation equation, mass conservation equation, energy conservation equation and heat transfer rate equation. The micro-element is then iteratively solved to obtain the dynamic simulation model of the entire drying chamber: Where, M is the moisture content of grain; K is the drying rate coefficient; M e Balance grain moisture content for drying; In the formula, H in and H out is the moisture content of the inlet and outlet of the micro-element wet air in the drying chamber; x in and x out is the mass fraction of water vapor at the inlet and outlet of the drying chamber micro-element wet air; ρ g is the dry microelement grain density, kg / m 3 ; A is the contact area between wet air and grain, m 2 ; ΔL is the dry microelement thickness, m; m in is the mass flow rate of wet air at the inlet of the dry microelement, kg / s; Where M0 is the initial moisture content of grain; out is the wet air mass flow rate at the outlet of the dry microelement, kg / s; In the formula, h cv is the heat transfer coefficient between grain and moist air, kW / (m 2 .℃); c w is the specific heat capacity of water vapor at constant pressure, kJ / (kg.℃); c a is the constant pressure specific heat capacity of dry air, kJ / (kg.℃); T in and T out T is the inlet and outlet temperature of the dry micro-element wet air, °C; g is the grain temperature, °C; In the formula, c g is the specific heat capacity of grain at constant pressure, kJ / (kg.K); c l is the specific heat capacity of water at constant pressure, kJ / (kg.K); L a is the latent heat of vaporization, kJ / kg; S222: Regenerator Dynamic Modeling: The regenerator uses a plate heat exchanger. During the dynamic response of the regenerator, the mass conservation equation, pressure drop equation and energy conservation equation of the wet air and water film on the metal wall surface on both sides are based on formulas (5) and (6); S223: Fan Dynamic Modeling: The operation process of the fan is also considered as a transient process, and the power consumption of the fan is: Where V a is the fresh air volume flow rate, m 3 / s;p a is the fresh air pressure, kPa; η f is the fan efficiency.

4. The method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica according to claim 1, characterized in that: Step 3 is as follows: add a two-phase flow inlet connector and a two-phase flow outlet connector to the compressor model; add a two-phase flow inlet connector and a two-phase flow outlet connector to the expansion valve model; add a two-phase flow inlet connector, a two-phase flow outlet connector, a wet air inlet connector, and a wet air outlet connector to the evaporator and condenser models; place a wet air inlet connector and a wet air outlet connector in the fan model; place a wet air inlet connector and a wet air outlet connector in the drying chamber model; place two wet air inlet connectors and two wet air outlet connectors in the regenerator model; among which, the fan inlet connector is connected to the atmospheric environment, and the fan outlet connector It is connected to the wet air inlet connector of the condenser, the wet air outlet connector of the condenser is connected to the drying chamber inlet connector, the drying chamber outlet connector is connected to the first wet air inlet connector of the regenerator, the first wet air outlet connector of the regenerator is connected to the wet air inlet connector of the evaporator, and the wet air outlet connector of the evaporator leads to the external environment to form a drying circuit; the two-phase flow outlet connector of the compressor is connected to the two-phase flow inlet connector of the condenser, the two-phase flow outlet connector of the condenser is connected to the two-phase flow inlet connector of the expansion valve, the two-phase flow outlet connector of the expansion valve is connected to the two-phase flow inlet connector of the evaporator, and the two-phase flow outlet connector of the evaporator is connected to the two-phase flow inlet connector of the compressor to form a heat pump circuit.

5. The method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica according to claim 1, characterized in that: Step 4 is as follows: set the fresh air volume to 0.5kg / s, set the ambient temperature to 20℃, set the ambient relative humidity to 70%, set the drying temperature to 55℃, the initial moisture content of the grain to 0.3, the target moisture content to 0.14, the initial mass to 100kg, and the length, width and height of the drying chamber to 0.4m, 0.4m and 1.1m respectively; when the rated grain moisture content target is reached, the temperature of the wet air at the drying chamber outlet ranges from 37.6℃ to 50.3℃, and the relative humidity ranges from 72% to 56%, providing safety boundary conditions for the subsequent heat pump loop parameter design and PID control design.

6. The method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica according to claim 1, characterized in that: Step 5 specifically includes the following steps: S51: Based on the dynamic models of the drying circuit and the heat pump circuit, a dynamic simulation model of the entire heat pump drying system is constructed; S52: Based on the operating range of the temperature and relative humidity of the wet air at the outlet of the drying chamber provided in S4, the operating parameters of each key device in the heat pump circuit are adjusted, including the volume and speed of the compressor, the flow area of ​​the expansion valve, and the heat exchange structure parameters of the condenser and the evaporator, to perform open-loop simulation operation; since the outlet temperature of the drying chamber is the lowest and the waste heat recovery effect is the worst at the initial stage of drying, the heat pump circuit needs to be debugged at the initial stage of drying to meet the system operating conditions under this extreme condition, including the drying temperature and superheat. When the drying temperature is lower than the set value, the volume and speed of the compressor and the heat exchange area of ​​the condenser are increased. When the drying temperature exceeds the set value, the opposite operation is performed to make the drying temperature near the set value at the initial stage of drying; when the superheat is lower than the set value, the flow area of ​​the expansion valve and the heat exchange area of ​​the evaporator are increased. When the superheat exceeds the set value, the opposite operation is performed to make the superheat near the set value at the initial stage of drying; in addition, due to the integrated coupling characteristics of the system, the drying temperature and the superheat are severely coupled, and the two are positively correlated and affect each other; Therefore, during the parameter debugging process, the debugging range can be reduced to avoid overshoot; based on the above debugging results, the volume parameters of the compressor, the heat exchange structure parameters of the evaporator and condenser, and the initial values ​​of the compressor speed and expansion valve opening are provided for the subsequent PID controller design; S53: Design a PID controller, set the controlled variable y to the drying temperature y1 and the superheat y2, the drying temperature y1 is set to 55°C, the superheat y2 is set to 5°C, and the control object u is set to the expansion valve opening u1 and the compressor speed u2; according to the different control objects, two control schemes are obtained: Scheme 1, expansion valve opening u1 and compressor speed u2, the expansion valve opening is used to control the drying temperature, and the compressor speed is used to control the superheat; Scheme 2, compressor speed u1 and expansion valve opening u2, the compressor speed is used to control the drying temperature, and the expansion valve opening is used to control the superheat; Based on the structural parameters of the compressor, condenser and evaporator provided in S52, as well as the initial values ​​of the compressor speed and the expansion valve opening, debug the parameter K in the PID controller in the two control schemes p , K i and K d , and compare and analyze the feasibility and superiority of the two control schemes.

7. The method for dynamic modeling of drying chamber characteristics and heat pump drying system based on Modelica according to claim 1, characterized in that: Step 6 specifically includes the following steps: S61: Set the initial fresh air mass flow rate to 0.5kg / s, increase it to 0.55kg / s at 7000s, and then decrease it to 0.45kg / s at 10000s. Adjust the step process of the fresh air mass flow rate. Under this step condition, adjust the dynamic response process of the humid air heat absorption in the condenser, the compressor and the fan power consumption. The fresh air mass flow rate increases stepwise, and the compressor power consumption, fan power consumption and humid air heat absorption all increase suddenly. The increase in fan power consumption is caused by the step increase in the fresh air flow rate, and its power consumption is positively correlated with the fresh air mass flow rate; the compressor power consumption is first ignored. It gradually increases after a slight decrease. This is because the compressor speed is used to control the superheat. The superheat has a step-up phenomenon at the beginning of the step, so the compressor speed is reduced at the initial stage; the heat absorption of wet air in the condenser shows a two-stage trend, first a step-up, then a slight decrease and then an increase. This is a step increase in the mass flow of fresh air. The heat exchange area is more fully utilized, and more heat is taken away instantly. The subsequent trend corresponds to the law of the compressor speed, which first decreases and then increases. When the mass flow of fresh air decreases in a step, the power consumption of the compressor, the power consumption of the fan and the heat absorption of wet air have opposite responses. S62: Dynamic response process of adjusting drying temperature and superheat. The fresh air mass flow rate increases in steps. The heat released by the refrigerant in the condenser cannot meet the demand of wet air. The drying temperature drops sharply. The PID control intervenes to reduce the expansion valve opening and the outlet refrigerant pressure decreases. Therefore, the superheat will have an initial reverse phenomenon, showing a trend of first increasing in steps and then decreasing. Since the compressor speed is used to control the superheat, the compressor power consumption will also change accordingly, first slightly decreasing and then increasing. The fresh air mass flow rate decreases in steps. The heat released by the refrigerant in the condenser exceeds the demand of wet air. The drying temperature increases sharply. The PID control intervenes to increase the expansion valve opening and the outlet refrigerant pressure increases. Therefore, the superheat will first decrease in steps and then increase. In addition, since the superheat is affected by the expansion valve opening and the compressor speed at the same time, it is also affected by the expansion valve outlet refrigerant pressure and flow rate. Therefore, the sensitivity of the superheat under disturbance is much higher than that of the drying temperature. The step increase of the fresh air mass flow rate is the opposite. S63: Adjust the dynamic response process of the heat pump performance coefficient COP and the dehumidification capacity per unit energy consumption SMER. The fresh air mass flow rate increases step by step. Since the amount of heat absorbed by the humid air increases step by step, and there is a response time for the increase in the compressor speed, the COP first increases step by step and then decreases, while the SMER decreases significantly. Although the increase in the fresh air quality will lead to an increase in the drying rate of the drying chamber to a certain extent, its increase rate is much smaller than the increase rate of the compressor power consumption and the fan power consumption, while the step decrease in the fresh air flow rate is the opposite. In addition, as the drying process proceeds, the COP gradually increases, while the SMER gradually decreases. This is because the temperature of the humid air at the outlet of the drying chamber continues to increase, the amount of waste heat recovered in the regenerator increases, the compressor power consumption increases and decreases, while the drying rate decreases at a rate much higher than the compressor power consumption decreases, so the SMER gradually decreases.

8. A computer device comprising a memory, a processor and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method of claim 1.

9. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the method according to claim 1 are implemented.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to claim 1 are implemented.

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