Simulation method and system for operation process of variable frequency unit of refrigerated container

Abstract

This invention discloses a simulation method and system for the operation of a variable frequency drive unit in a refrigerated container. The method includes constructing a simplified simulation model and setting initial system parameters; periodically calculating the real-time values ​​of evaporation and condensation pressures based on refrigerant flow balance using the simplified simulation model; determining the target evaporation pressure based on the operating mode and the container temperature, and dynamically adjusting the opening value of the electronic expansion valve using a proportional-integral (PI) control algorithm based on the real-time evaporation pressure to bring the evaporation pressure close to the target evaporation pressure; calculating the periodic change in the container temperature based on the compressor speed, evaporator fan speed, and container temperature control deviation, and obtaining the return air temperature and supply air temperature based on the container temperature; and finally displaying the results through a human-machine interface. This invention effectively overcomes the problems of high maintenance and testing costs, unintuitive teaching simulations, lack of process control logic, and difficulties in simulating advanced functions in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of simulation technology for variable frequency drives (VFDs) in refrigerated containers, and in particular to a simulation method and system for the operation of VFDs in refrigerated containers. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Refrigerated containers, as core equipment in cold chain transportation, require precise control of their internal environment and reliable operation. Variable frequency drives (VFDs) are widely used due to their excellent energy-saving performance. To ensure effective evaluation of these units during maintenance, training, and design verification phases, a simulation method and system that can realistically simulate their operation and is easy for operators to understand and learn is of significant practical importance.

[0004] In existing technologies, there are three main approaches to the simulation and testing of refrigerated container units: The first is learning through actual unit operation, which is direct functional testing based on physical equipment. This involves connecting the single or multiple control units under test (such as CPU boards, I / O boards) to a test bench containing actual compressors, fans, sensors, and other loads for power-on testing. This method relies on the operation of real physical components; the test bench is bulky, costly, space-consuming, energy-intensive, noisy, and inefficient, and it cannot visually demonstrate the evolution of internal thermodynamic processes. Secondly, the simulation test bench using a real controller is suitable for the repair and testing of control unit components. However, the parameters cannot change continuously according to the system process, which is not conducive to the simulation demonstration of the complete working process and cannot realize the complete PTI function demonstration.

[0005] Thirdly, there are high-precision thermodynamic system simulations (computer simulations). These models are often based on detailed fluid dynamics and thermodynamic equations, aiming to accurately predict the performance parameters of the unit under different environments. However, such models are usually complex in structure, computationally intensive, and have high requirements for hardware platforms. They also have poor interface interactivity, mainly serving professional designers and are difficult to directly apply to rapid fault location in maintenance sites or intuitive teaching demonstrations in training sites.

[0006] In summary, existing technologies provide basic means for the testing and simulation of generator units, but significant shortcomings still exist: Maintenance testing is inefficient and costly: Direct testing methods based on physical loads require connection to high-power equipment such as compressors and fans, resulting in large test benches, significant energy consumption, and operating noise. This raises the barrier to entry and increases the cost of maintenance testing.

[0007] The disconnect between simulation and training applications: While high-precision thermodynamic simulation models can reflect the physical nature of a system, their "black box" calculation process and complex parameter setting interface make them difficult for maintenance personnel or trainees without a professional background to understand. They also lack intuitive visual interfaces to demonstrate dynamic processes such as refrigerant flow and valve operation, thus limiting their effectiveness in operational training and fault demonstration.

[0008] Lack of process control-oriented teaching simulation: Existing simulation technologies often focus on steady-state performance verification or single-component functional testing, lacking a simulation method that can completely and continuously simulate the switching of multiple operating modes and the dynamic process of control logic of the unit. This makes it difficult for trainees to grasp the overall working logic and control flow of the system. Summary of the Invention

[0009] To address the aforementioned issues, this invention proposes a simulation method and system for the operation of a variable frequency drive unit in a refrigerated container. This invention constructs a simulation model and method that balances simplicity, intuitiveness, and completeness, effectively overcoming problems such as high maintenance and testing costs, unintuitive teaching simulations, lack of process control logic, and difficulties in simulating advanced functions in existing technologies.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a simulation method for the operation of a variable frequency drive unit in a refrigerated container, comprising the following steps: A simplified simulation model of the variable frequency unit's refrigeration system was constructed, and initial system parameters were set. Based on a simplified simulation model, the real-time values ​​of evaporation pressure and condensation pressure are calculated periodically based on refrigerant flow balance iterations. The target evaporation pressure is determined based on the operating mode and the temperature inside the chamber. Based on the real-time value of the evaporation pressure, the opening value of the electronic expansion valve is dynamically adjusted using a proportional-integral (PI) control algorithm to make the evaporation pressure approach the target evaporation pressure. Based on the compressor speed, evaporator fan speed, and chamber temperature control deviation, the periodic change in chamber temperature is calculated, and the return air temperature and supply air temperature are obtained based on the chamber temperature. The simulation-derived evaporation pressure, condensation pressure, electronic expansion valve opening value, chamber temperature, return air temperature, and supply air temperature, as well as the equipment operating status of the compressor, fan, and solenoid valve determined based on the simulation model, are output to the human-machine interface for centralized visualization and monitoring.

[0011] As an alternative implementation, the initial system parameters include condensation pressure, evaporation pressure, chamber temperature, ambient temperature, and operating mode settings.

[0012] As an optional implementation, the specific method for calculating the real-time value of the evaporation pressure is as follows: periodically calculate the difference between the refrigerant mass flow rate flowing through the electronic expansion valve and the refrigerant mass flow rate of the compressor to obtain a first difference, and iteratively update the evaporation pressure based on the first difference; wherein, the refrigerant mass flow rate flowing through the electronic expansion valve is expressed as: ;in, This refers to the refrigerant mass flow rate passing through the electronic expansion valve. The pressure difference across the expansion valve. This represents the current opening degree of the electronic expansion valve; The refrigerant mass flow rate of the compressor is expressed as: ;in, This refers to the refrigerant mass flow rate of the compressor. The reference value is a constant. The compressor speed influence coefficient. The coefficient representing the influence of inhalation pressure. This refers to the compressor speed. This refers to the compressor's suction pressure.

[0013] As an optional implementation, the specific method for calculating the real-time value of the condensing pressure is as follows: periodically calculate the difference between the refrigerant mass flow rate of the compressor and the condensation capacity of the condenser to obtain a second difference, and iteratively update the condensing pressure based on the second difference; wherein, the condensation capacity of the condenser is expressed as: ;in, The condensing capacity of the condenser. This is the condenser fan speed coefficient. For ambient temperature, This is the condensation temperature.

[0014] As an alternative implementation, a proportional-integral (PI) control algorithm is used to dynamically adjust the opening value of the electronic expansion valve, expressed as: ; ; in, This is the pressure deviation value. Set the evaporation pressure value. This is the actual value of the evaporation pressure. This refers to the number of pulses required to open the electronic expansion valve. This is the proportionality coefficient. is the integral coefficient.

[0015] As an alternative implementation method, calculating the periodic change in temperature inside the chamber is equivalent to calculating the temperature change over a fixed time interval, specifically expressed as follows: ; in, This represents the temperature change inside the chamber at fixed intervals; negative values ​​are used for cooling mode and positive values ​​for heating mode. This represents the temperature change inside the casing corresponding to the compressor speed. This is the influence coefficient corresponding to the evaporator fan speed. This represents the influence coefficient corresponding to the temperature control deviation in the chamber.

[0016] As an alternative implementation, the method of obtaining the return air temperature and supply air temperature based on the internal temperature of the chamber specifically involves: The calculated internal temperature of the chamber is directly used as the return air temperature. When the operating mode is cooling, a preset supply air temperature difference value related to the temperature control deviation inside the box is subtracted from the return air temperature to obtain the supply air temperature; when the operating mode is heating, a preset supply air temperature difference value related to the temperature control deviation inside the box is added to the return air temperature to obtain the supply air temperature; wherein the temperature control deviation inside the box is the difference between the actual value of the temperature inside the box and its set value.

[0017] Secondly, the present invention provides a simulation system for the operation of a variable frequency unit in a refrigerated container, comprising the following modules: The simulation model construction and initialization module is configured to: construct a simplified simulation model of the variable frequency unit's refrigeration system and set the initial system parameters; The pressure simulation module is configured to periodically calculate the real-time values ​​of evaporation pressure and condensation pressure based on a simplified simulation model and refrigerant flow balance. The expansion valve control module is configured to: determine the target evaporation pressure based on the operating mode and the temperature inside the chamber, and dynamically adjust the opening value of the electronic expansion valve based on the real-time value of the evaporation pressure using a proportional-integral (PI) control algorithm, so that the evaporation pressure approaches the target evaporation pressure; The chamber environment simulation module is configured to: calculate the periodic change of the chamber temperature based on the compressor speed, evaporator fan speed and chamber temperature control deviation, and obtain the return air temperature and supply air temperature based on the chamber temperature. The visualization module is configured to output the simulated evaporation pressure, condensation pressure, electronic expansion valve opening value, box temperature, return air temperature and supply air temperature, as well as the equipment operating status of the compressor, fan and solenoid valve determined based on the simulation model, to the human-machine interface for centralized visualization display and monitoring.

[0018] Thirdly, the present invention provides an electronic device, including a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, complete the simulation method for the operation process of a refrigerated container variable frequency unit as described in the first aspect.

[0019] Fourthly, the present invention provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, complete the simulation method for the operation process of a refrigerated container variable frequency unit as described in the first aspect.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention constructs a simplified simulation model, eliminating the reliance on physical compressors, fans, and refrigerant piping in traditional testing. This makes the testing system lightweight, noiseless, and energy-efficient, significantly reducing equipment purchase, operation, and maintenance costs. Furthermore, by eliminating the limitations of physical equipment, testing can be performed repeatedly, greatly improving the convenience and efficiency of maintenance testing and training.

[0021] This invention simplifies the complex thermodynamics and control processes of refrigeration systems into a dynamic calculation model centered on flow balance and PI control. This simplified model has a low computational burden and can run in real-time on ordinary PLCs or PCs, meeting the immediacy requirements of teaching demonstrations. Furthermore, this invention displays all internal calculation processes and final operating states through a human-machine interface, making the previously invisible internal logic and physical processes intuitive and visible. This allows trainees to clearly understand the complete control chain from setpoint input to system state response, significantly improving teaching effectiveness.

[0022] This invention not only simulates a single refrigeration state, but also guides the simulation model to follow control logic consistent with actual units through the input of "operating mode". By setting the target evaporation pressure and using a PI control algorithm, it realistically simulates the dynamic adjustment process of the electronic expansion valve in different modes such as refrigeration and heating. Simultaneously, it calculates the internal temperature change based on compressor / fan speed and chamber temperature deviation, and derives the return / supply air temperature. This allows the system to realistically demonstrate the switching and operation of multiple operating modes, providing trainees with a comprehensive and practical operating experience.

[0023] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a flowchart illustrating the simulation method for the operation of a variable frequency unit in a refrigerated container, as provided in Embodiment 1 of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] It should be noted that the following detailed description is exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0029] Example 1 like Figure 1 As shown, this embodiment provides a simulation method for the operation of a refrigerated container variable frequency unit. It is implemented through programming in a programmable logic controller (PLC). The core of this method lies in building and running a simplified refrigeration system simulation model to efficiently and intuitively simulate the actual operation of the unit. The specific steps are as follows: S1: Construct a simplified simulation model of the variable frequency unit's refrigeration system and set the initial system parameters.

[0030] In step S1, a simplified simulation model (refrigeration system model) is constructed in the PLC. The core of the simplified simulation model includes four major components: compressor, condenser, electronic expansion valve (EEV), and evaporator.

[0031] And set the initial system parameters for the simplified simulation model, specifically including: condensing pressure. Evaporation pressure (Initial values ​​can be set to compressor suction pressure), internal temperature, ambient temperature, and operating mode settings.

[0032] S2: Based on the simplified simulation model, the real-time values ​​of evaporation pressure and condensation pressure are calculated periodically based on refrigerant flow balance iteration.

[0033] In step S2, based on the principle of flow balance, the evaporation pressure is calculated iteratively at a fixed time period (e.g., every 1 second). and condensation pressure The real-time value.

[0034] The specific method for calculating the real-time value of evaporation pressure is as follows: Periodically calculate the refrigerant mass flow rate through the electronic expansion valve. Refrigerant mass flow rate of the compressor The difference is used to obtain the first difference, and the evaporation pressure is iteratively updated based on the first difference; more specifically: The refrigerant mass flow rate through the electronic expansion valve is expressed as: ;in, This refers to the refrigerant mass flow rate passing through the electronic expansion valve. ( The pressure difference across the expansion valve is denoted as . This represents the current opening degree of the electronic expansion valve (expressed in pulse count, 0 for fully closed, 427 for fully open). The refrigerant mass flow rate of the compressor is expressed as: ;in, This refers to the refrigerant mass flow rate of the compressor. The reference value is a constant. The compressor speed influence coefficient. The coefficient representing the influence of inhalation pressure. This refers to the compressor speed. This refers to the compressor's suction pressure.

[0035] Change in evaporation pressure ;in, Let be the influence coefficient, and be a constant. Superimposed on the previous cycle The new real-time value of the evaporation pressure is obtained from the value.

[0036] The specific method for calculating the real-time value of condensing pressure is as follows: periodically calculate the difference between the refrigerant mass flow rate of the compressor and the condensation rate of the condenser to obtain a second difference, and iteratively update the condensing pressure based on the second difference; more specifically: The condensing capacity of the condenser is expressed as follows: ;in, The condensing capacity of the condenser. This is the condenser fan speed coefficient. For ambient temperature, This is the condensation temperature.

[0037] Change in condensing pressure in, Let be the influence coefficient, and be a constant. Superimposed on the previous cycle The new real-time value of the condensing pressure is obtained from the value. During normal refrigeration operation, the compressor discharge pressure is considered. equal .

[0038] S3: Determine the target evaporation pressure based on the operating mode and the temperature inside the chamber, and dynamically adjust the opening value of the electronic expansion valve based on the real-time value of the evaporation pressure using a proportional-integral (PI) control algorithm to make the evaporation pressure approach the target evaporation pressure.

[0039] In step S3, the target evaporation pressure is determined according to the currently set operating mode (refrigeration or freezing) and the internal temperature, based on preset rules. For example, in refrigeration mode, when the box temperature is ≥10℃, Set to 249 kPa (corresponding to an evaporation temperature of 5℃); when the chamber temperature is between -10℃ and 10℃... It varies linearly between 64 kPa and 249 kPa.

[0040] The opening value of the electronic expansion valve is dynamically adjusted using a proportional-integral (PI) control algorithm, expressed as: ; ; in, This is the pressure deviation value. Set the evaporation pressure value. This is the actual value of the evaporation pressure. This refers to the number of pulses required to open the electronic expansion valve. This is the proportionality coefficient. is the integral coefficient.

[0041] S4: Based on the compressor speed, evaporator fan speed, and chamber temperature control deviation, the periodic change in the chamber temperature is calculated, and the return air temperature and supply air temperature are obtained based on the chamber temperature.

[0042] In step S4, the temperature inside the chamber is calculated as follows: the temperature change inside the chamber at each fixed time interval is specifically expressed as follows: ; in, This represents the temperature change inside the chamber at fixed intervals; negative values ​​are used for cooling mode and positive values ​​for heating mode. This represents the temperature change inside the compressor chamber corresponding to the compressor speed. The higher the speed, the higher the temperature change. The larger the absolute value, This is the influence coefficient corresponding to the evaporator fan speed. This is the influence coefficient corresponding to the temperature control deviation in the chamber; the larger the deviation, the greater the influence coefficient. The larger the value. During cooling operation. Take a negative value; take a positive value during heating operation. The temperature is accumulated to the current internal temperature of the chamber to obtain a new internal temperature value.

[0043] The return air temperature and supply air temperature are obtained based on the temperature inside the chamber, specifically: The calculated internal temperature of the chamber is directly used as the return air temperature. When the operating mode is cooling, a preset supply air temperature difference value related to the temperature control deviation inside the box is subtracted from the return air temperature to obtain the supply air temperature; when the operating mode is heating, a preset supply air temperature difference value related to the temperature control deviation inside the box is added to the return air temperature to obtain the supply air temperature; wherein the temperature control deviation inside the box is the difference between the actual value of the temperature inside the box and its set value.

[0044] S5: The simulation results of evaporation pressure, condensation pressure, electronic expansion valve opening value, box temperature, return air temperature and supply air temperature, as well as the equipment operating status of compressor, fan and solenoid valve determined based on the simulation model, are output to the human-machine interface for centralized visualization and monitoring.

[0045] In step S5, all key system state parameters obtained from simulation calculations in S2 to S4, including evaporation pressure, are processed. Condensing pressure The system outputs the following data to the human-machine interface (HMI): electronic expansion valve opening pulse count, chamber temperature, return air temperature, supply air temperature, and operating status (start / stop, high / low speed, open / close) of the compressor, condenser fan, evaporator fan, and various solenoid valves (LSV, HSV, ESV, RSV) determined by the simulation model logic (such as pressure and temperature threshold judgment).

[0046] Example 2 This embodiment provides a simulation system for the operation of a variable frequency drive unit in a refrigerated container, including the following modules: The simulation model construction and initialization module is configured to: construct a simplified simulation model of the variable frequency unit's refrigeration system and set the initial system parameters; The pressure simulation module is configured to periodically calculate the real-time values ​​of evaporation pressure and condensation pressure based on a simplified simulation model and refrigerant flow balance. The expansion valve control module is configured to: determine the target evaporation pressure based on the operating mode and the temperature inside the chamber, and dynamically adjust the opening value of the electronic expansion valve based on the real-time value of the evaporation pressure using a proportional-integral (PI) control algorithm, so that the evaporation pressure approaches the target evaporation pressure; The chamber environment simulation module is configured to: calculate the periodic change of the chamber temperature based on the compressor speed, evaporator fan speed and chamber temperature control deviation, and obtain the return air temperature and supply air temperature based on the chamber temperature. The visualization module is configured to output the simulated evaporation pressure, condensation pressure, electronic expansion valve opening value, box temperature, return air temperature and supply air temperature, as well as the equipment operating status of the compressor, fan and solenoid valve determined based on the simulation model, to the human-machine interface for centralized visualization display and monitoring.

[0047] It should be noted that the above modules correspond to the steps in Embodiment 1, and the examples and application scenarios implemented by the above modules and their corresponding steps are the same, but are not limited to the content disclosed in Embodiment 1. It should also be noted that the above modules can be executed in a computer system as part of the system.

[0048] In further embodiments, the following is also provided: An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, perform the method described in Embodiment 1. For brevity, further details are omitted here.

[0049] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0050] A computer-readable storage medium for storing computer instructions that, when executed by a processor, perform the method of Embodiment 1.

[0051] The method in Example 1 can be directly executed by a hardware processor, or it can be executed by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0052] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A simulation method for the operation of a variable frequency drive unit in a refrigerated container, characterized in that, include: A simplified simulation model of the variable frequency unit's refrigeration system was constructed, and initial system parameters were set. Based on a simplified simulation model, the real-time values ​​of evaporation pressure and condensation pressure are calculated periodically based on refrigerant flow balance iterations. The target evaporation pressure is determined based on the operating mode and the temperature inside the chamber. Based on the real-time value of the evaporation pressure, the opening value of the electronic expansion valve is dynamically adjusted using a proportional-integral (PI) control algorithm to make the evaporation pressure approach the target evaporation pressure. Based on the compressor speed, evaporator fan speed, and chamber temperature control deviation, the periodic change in the chamber temperature is calculated, and the return air temperature and supply air temperature are obtained based on the chamber temperature. The simulation-derived evaporation pressure, condensation pressure, electronic expansion valve opening value, chamber temperature, return air temperature, and supply air temperature, as well as the equipment operating status of the compressor, fan, and solenoid valve determined based on the simulation model, are output to the human-machine interface for centralized visualization and monitoring.

2. The simulation method for the operation of a refrigerated container variable frequency unit as described in claim 1, characterized in that, The initial system parameters include condensation pressure, evaporation pressure, chamber temperature, ambient temperature, and operating mode settings.

3. The simulation method for the operation of a refrigerated container variable frequency unit as described in claim 1, characterized in that, The specific method for calculating the real-time value of the evaporation pressure is as follows: periodically calculate the difference between the refrigerant mass flow rate through the electronic expansion valve and the refrigerant mass flow rate through the compressor to obtain a first difference, and iteratively update the evaporation pressure based on the first difference; wherein, the refrigerant mass flow rate through the electronic expansion valve is expressed as: ;in, This refers to the refrigerant mass flow rate passing through the electronic expansion valve. The pressure difference across the expansion valve. This represents the current opening degree of the electronic expansion valve; The refrigerant mass flow rate of the compressor is expressed as: ;in, This refers to the refrigerant mass flow rate of the compressor. The reference value is a constant. The compressor speed influence coefficient. The coefficient representing the influence of inhalation pressure. This refers to the compressor speed. This refers to the compressor's suction pressure.

4. The simulation method for the operation of a refrigerated container variable frequency unit as described in claim 1, characterized in that, The specific method for calculating the real-time value of the condensing pressure is as follows: periodically calculate the difference between the refrigerant mass flow rate of the compressor and the condensing capacity of the condenser to obtain a second difference, and iteratively update the condensing pressure based on the second difference; wherein, the condensing capacity of the condenser is expressed as: ;in, The condensing capacity of the condenser. This is the condenser fan speed coefficient. For ambient temperature, This is the condensation temperature.

5. The simulation method for the operation of a variable frequency unit in a refrigerated container as described in claim 1, characterized in that, The opening value of the electronic expansion valve is dynamically adjusted using a proportional-integral (PI) control algorithm, expressed as: ； ； in, This is the pressure deviation value. Set the evaporation pressure value. This is the actual value of the evaporation pressure. This refers to the number of pulses required to open the electronic expansion valve. This is the proportionality coefficient. is the integral coefficient.

6. The simulation method for the operation of a refrigerated container variable frequency unit as described in claim 1, characterized in that, The periodic change in temperature inside the chamber is calculated as the temperature change over a fixed time interval, specifically expressed as: ； in, This represents the temperature change inside the chamber at fixed intervals; negative values ​​are used for cooling mode and positive values ​​for heating mode. This represents the temperature change inside the casing corresponding to the compressor speed. This is the influence coefficient corresponding to the evaporator fan speed. This represents the influence coefficient corresponding to the temperature control deviation in the chamber.

7. The simulation method for the operation of a refrigerated container variable frequency unit as described in claim 1, characterized in that, The return air temperature and supply air temperature are obtained based on the temperature inside the box, specifically as follows: The calculated internal temperature of the chamber is directly used as the return air temperature. When the operating mode is cooling, the supply air temperature is obtained by subtracting a preset supply air temperature difference value related to the temperature control deviation inside the box from the return air temperature; when the operating mode is heating, the supply air temperature is obtained by adding a preset supply air temperature difference value related to the temperature control deviation inside the box to the return air temperature. The temperature control deviation inside the chamber is the difference between the actual temperature inside the chamber and its set value.

8. A simulation system for the operation of a variable frequency unit in a refrigerated container, characterized in that, Includes the following modules: The simulation model construction and initialization module is configured to: construct a simplified simulation model of the variable frequency unit's refrigeration system and set the initial system parameters; The pressure simulation module is configured to periodically calculate the real-time values ​​of evaporation pressure and condensation pressure based on a simplified simulation model and refrigerant flow balance. The expansion valve control module is configured to: determine the target evaporation pressure based on the operating mode and the temperature inside the chamber, and dynamically adjust the opening value of the electronic expansion valve based on the real-time value of the evaporation pressure using a proportional-integral (PI) control algorithm, so that the evaporation pressure approaches the target evaporation pressure; The chamber environment simulation module is configured to: calculate the periodic change of the chamber temperature based on the compressor speed, evaporator fan speed and chamber temperature control deviation, and obtain the return air temperature and supply air temperature based on the chamber temperature. The visualization module is configured to output the simulated evaporation pressure, condensation pressure, electronic expansion valve opening value, box temperature, return air temperature and supply air temperature, as well as the equipment operating status of the compressor, fan and solenoid valve determined based on the simulation model, to the human-machine interface for centralized visualization display and monitoring.

9. An electronic device, characterized in that, The method includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, complete the simulation of the operation process of a refrigerated container variable frequency unit as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, Used to store computer instructions, which, when executed by a processor, complete the simulation method for the operation process of a refrigerated container variable frequency unit as described in any one of claims 1-7.

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