A precise regulation method for cold chain low-temperature environment

Abstract

The application relates to a cold-chain low-temperature environment precision regulation method and relates to the technical field of cold-chain logistics and refrigeration control. The method comprises the following steps: acquiring real-time operation parameters such as an evaporator outlet temperature, return air relative humidity, return air temperature, a vertical temperature distribution in a compartment and an electronic expansion valve opening degree, calculating a frosting risk index, and combining a dynamic threshold affected by an environment temperature and return air humidity to judge whether the current should enter three control states of stable-state refrigeration, pre-frosting suppression or active defrosting, so that the precision regulation of the cold-chain environment is realized. The application can effectively avoid unnecessary defrosting operation, reduce energy consumption, and simultaneously improve the stability and control precision of the temperature in the cold-chain compartment.

Description

Technical Field

[0001] This application relates to the field of cold chain logistics and refrigeration control technology, specifically to a method for precise control of low-temperature environment in cold chain. Background Technology

[0002] Cold chain logistics, a crucial link in ensuring the quality and safety of perishable goods such as food and medicine, relies on maintaining a constant low-temperature environment during transportation and storage. Current cold chain container technology commonly employs refrigeration systems equipped with variable frequency compressors, electronic expansion valves, and multi-outlet air supply mechanisms for temperature control. These systems typically collect basic parameters such as the container's internal temperature, evaporator temperature, and return air temperature and humidity, and use preset fixed logic or simple proportional-integral-derivative (PID) algorithms to adjust the compressor frequency and valve opening. When the evaporator surface temperature is detected to be below the dew point or the operating time reaches a set value, the system executes a standardized defrosting procedure, stopping the refrigeration cycle and activating the heating device to remove frost. Refrigeration operation is then resumed, and this cycle is repeated to maintain thermal balance within the container.

[0003] However, in actual long-term operation, existing technical solutions face the common challenge of insufficient frosting control precision and difficulty in achieving both energy efficiency and stability. Due to frequent fluctuations in the external environment and the complex and variable loading conditions inside the container, fixed defrosting triggering mechanisms often fail to accurately match the actual frosting trend. This leads to unnecessary defrosting operations when there is no significant risk of frosting, or failure to intervene in time at the initial stage of frosting, resulting in a sharp drop in heat exchange efficiency. This mismatch between the control strategy and actual operating conditions causes problems such as large temperature fluctuations inside the cold chain container, reduced refrigeration efficiency ratio, and limited equipment operational stability, making it difficult to meet the dual stringent requirements of high-quality cold chain transportation for a constant temperature environment and low energy consumption. Summary of the Invention

[0004] This application provides a method for precise control of low-temperature environment in cold chain, which can solve the common challenges faced by existing technical solutions, such as insufficient frosting control precision and difficulty in balancing energy consumption efficiency. This leads to unnecessary defrosting operations when there is no significant risk of frosting, or failure to intervene in time at the beginning of frosting, resulting in a sharp drop in heat exchange efficiency, causing large temperature fluctuations in the cold chain compartment, reduced refrigeration energy efficiency ratio, and limited equipment operation stability.

[0005] To achieve the above objectives, this application provides the following technical solution: The present application provides a precise regulation method for cold chain low-temperature environments, which is applicable to a cold chain compartment equipped with a variable-frequency compressor, an electronic expansion valve, an evaporator, a multi-air-outlet air supply mechanism, a return air humidity sensor, an evaporator temperature sensor and a compartment interior temperature sensor. The method includes the following steps: S1: Acquire real-time operating parameters, where the real-time operating parameters include: evaporator outlet temperature T1, return air relative humidity RH1, return air temperature T2, compartment interior vertical temperature distribution T(z,t), and electronic expansion valve opening A1; calculate a frosting risk index R1 based on the difference between the return air relative humidity RH1 and the evaporator outlet temperature T1: R1= RH1× (T2- T1) / ΔT0; where ΔT0 is a reference temperature difference constant; S2: Select to enter one of the following three control states according to the comparison result of the frosting risk index R1 and a dynamic threshold R2: when R1<R2, enter a steady-state cooling state; when R2≤ R1<1.5·R2, enter a pre-frost-suppression state; when R1≥1.5·R2, enter an active defrosting state; where the dynamic threshold R2 is calculated in real time by the following formula: R2= R0+a1· (T3- T0) + b1· (RH1-85%); R0 is a reference threshold, a1 and b1 are correction coefficients, T3 is the ambient temperature, and T0 is the target temperature.

[0006] In an optional embodiment, the reference temperature difference constant ΔT0 has a value of 10 to 15K, which is calibrated and determined before delivery according to the design working condition of the cold chain compartment; the correction coefficients a1, b1 and the reference threshold R0 are determined through a standard working condition calibration test before the cold chain compartment leaves the factory, and are solidified in the controller; the dynamic threshold R2 is recalculated in each control cycle, and the control cycle is 500 milliseconds, which ensures that the threshold is adaptively adjusted in real time with the ambient working condition.

[0007] In an optional embodiment, the method further includes S211: In the steady-state cooling state, the compressor frequency is subjected to PID closed-loop adjustment according to the target temperature deviation, the adjustment cycle is 1 second, the proportional gain coefficient is 0.8, the integral time is 120 seconds, and the differential time is 15 seconds.

[0008] In an optional embodiment, the method further includes S212: In the steady-state cooling state, the opening of the electronic expansion valve tracks the superheat at the evaporator outlet, the target superheat value is 5.5K, the allowable fluctuation range is ±0.5K, the adjustment step of the electronic expansion valve opening is 1.5% each time, and the opening of each air supply outlet is uniformly set to 100% to realize balanced air supply.

[0009] In an optional embodiment, the method further includes S221: In the pre-defrost state, the opening of the electronic expansion valve is gradually reduced at a rate of 3% per second within 3 seconds after entering the pre-defrost state, with a total reduction of 8% to 14% of the current opening; after the reduction, the evaporator wall temperature change is monitored. If the wall temperature increase does not reach 0.3K, an additional 2% reduction is made in the next control cycle; if the wall temperature increase exceeds 0.8K, a 1.5% adjustment is made in the next control cycle.

[0010] In an optional embodiment, the method further includes S222: In the pre-frost suppression state, the air volume ratio of the top and bottom air outlets is adjusted according to the vertical temperature difference ΔT1 inside the chamber: when ΔT1>1.5°C, the opening of the top air outlet is increased to 70% and the opening of the bottom air outlet is decreased to 30%, and the adjustment is completed within 2 seconds; when ΔT1≤1.5°C, the openings of both the top and bottom air outlets are restored to 50%, and the air is supplied evenly.

[0011] In an optional embodiment, the method further includes S231: In active defrosting mode, the compressor is immediately stopped, the electronic expansion valve is closed to 0% opening, and the defrosting heating device is turned on. The defrosting heating device starts at 80% of its rated power and continues for 30 seconds before rising to 100% of its rated power.

[0012] In an optional embodiment, it further includes S232: In the active defrosting state, the defrosting termination condition is that the evaporator outlet temperature T1 ≥ 2°C and the duration exceeds 30 seconds, or the total defrosting time exceeds the preset maximum defrosting time of 15 minutes; after defrosting, the defrosting heating device is turned off, the compressor is restarted after waiting for 30 seconds, and the opening of the electronic expansion valve is restored to the opening before entering the active defrosting state, and then it returns to the steady-state refrigeration state.

[0013] In an optional embodiment, it further includes S233: during the active defrosting state, the blower operates in reverse mode, the reverse air speed is 30% to 60% of the normal air supply speed, the reverse start delay is 5 seconds after the start of defrosting, the reverse duration is 80% of the total defrosting time, and the forward air supply is restored 30 seconds before the end of defrosting to exhaust residual heat.

[0014] In one optional embodiment, when a door opening event is detected, the dynamic threshold is corrected based on the cumulative opening time t0 and the number of people entering and exiting n1: R3 = R2 × (1 - 0.2 × t0 / t1 - 0.1 × n1 / 5); where t1 is the control cycle, and the active defrosting state is forcibly exited during the door opening period. If defrosting is in progress, it is paused and switched to the pre-defrosting state until it resumes after the door is closed. During the defrosting pause, the defrosting heating device stops working, the compressor remains in a stopped state, and the blower resumes positive low-speed air supply with a wind speed of 20% of the normal air supply wind speed.

[0015] This application provides a method for precise control of low-temperature environments in the cold chain. The scheme acquires real-time operating parameters such as evaporator outlet temperature, return air relative humidity, return air temperature, vertical temperature distribution within the compartment, and electronic expansion valve opening. Based on the difference between return air relative humidity and evaporator outlet temperature, a frosting risk index R1 is constructed. This index is then compared in real-time with a dynamic threshold R2, which is affected by ambient and target temperatures. This allows the system to precisely switch between steady-state cooling, pre-frost suppression, and active defrosting states based on the comparison results. By introducing the frosting risk index R1 to quantitatively assess the likelihood of frosting and using the dynamic threshold R2 to compensate for environmental and humidity fluctuations in real time, adaptive matching between the control strategy and actual operating conditions is achieved. This effectively avoids misjudgments caused by fixed thresholds and reduces unnecessary defrosting operations. Furthermore, the tiered control strategy can employ differentiated adjustment methods at different risk levels, ensuring efficient cooling in low-risk conditions and early intervention when risks first appear, thereby achieving a stable balance between temperature control and optimized energy consumption within the cold chain compartment.

[0016] This effectively solves the common challenge of insufficient frosting control precision and difficulty in balancing energy efficiency in existing technical solutions. This leads to unnecessary defrosting operations when there is no significant risk of frosting, or a sharp drop in heat exchange efficiency due to failure to intervene in time at the beginning of frosting. This results in large temperature fluctuations, reduced refrigeration efficiency ratio, and limited equipment operation stability in the cold chain compartment. Therefore, it avoids drastic temperature fluctuations and energy waste caused by improper frosting control, and improves the overall operational reliability of the cold chain system and the quality of goods preservation. Attached Figure Description

[0017] Figure 1 A flowchart of a method for precise control of low-temperature environment in cold chain provided in this application; Figure 2 The flowchart shows the process of gradually reducing the opening of the pre-frost-suppressing electronic expansion valve and adjusting it based on the wall temperature change in the precise control method for cold chain low-temperature environment provided in this application. Figure 3 A flowchart illustrating the method for precise control of cold chain low-temperature environment provided in this application, which adjusts the air volume ratio of the top and bottom air outlets based on the vertical temperature difference inside the compartment. Figure 4 A flowchart illustrating the process of terminating defrosting and restoring steady-state refrigeration based on temperature duration or total duration in the precise control method for cold chain low-temperature environment provided in this application; Figure 5 The flowchart illustrates how the method for precise control of low-temperature cold chain environment provided in this application corrects the dynamic threshold and forcibly exits or pauses the active defrosting state when a door opening event is detected. Detailed Implementation

[0018] The present application will now be described in further detail with reference to embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the scope of the application.

[0019] like Figure 1 The diagram shown is a flowchart of a method for precise control of low-temperature environment in a cold chain provided in an embodiment of this application. The method includes: Step S1: Obtain real-time operating parameters, including: evaporator outlet temperature T1, return air relative humidity RH1, return air temperature T2, vertical temperature distribution inside the chamber T(z,t) and electronic expansion valve opening A1; The aforementioned real-time operating parameters are collected through a sensor network and actuator feedback loop deployed in the cold chain system. Specifically, the evaporator outlet temperature T1 reflects the evaporation pressure and heat exchange efficiency of the refrigeration system, and is collected by a temperature sensor (such as a platinum resistance thermometer or thermocouple) installed at the evaporator manifold outlet, and converted to a digital temperature value after analog-to-digital conversion. The return air relative humidity RH1 and return air temperature T2 characterize the humidity state of the air inside the compartment, and are acquired in real-time by a temperature and humidity composite sensor installed in the return air duct and transmitted to the control unit. The vertical temperature distribution inside the compartment T(z,t) describes the temperature gradient in the vertical direction of the internal space of the cold chain compartment. It is measured by an array of temperature sensors arranged at different height levels (such as the top, middle, and bottom) of the compartment, forming a spatial temperature data sequence that varies with time t and height z, used to monitor the temperature uniformity of the cargo stacking area. The electronic expansion valve opening A1 represents the degree of opening of the throttling mechanism valve core, usually expressed as a percentage (0%~100%), and is read directly from the feedback signal of the stepper motor controller or actuator driving the electronic expansion valve. The acquisition of multi-dimensional real-time operating parameters provides a comprehensive understanding of the current thermal state of the cold chain compartment, offering a data foundation for subsequent frost risk assessment and control decisions.

[0020] Based on the difference between the return air relative humidity RH1 and the evaporator outlet temperature T1, the frost risk index R1 is calculated: R1=RH1× (T2- T1) / ΔT0; Where ΔT0 is the reference temperature difference constant; The frosting risk index R1 is a dimensionless indicator that quantifies the likelihood of frosting on the evaporator surface. Its value is positively correlated with return air humidity and the temperature difference between the return air temperature and the evaporator outlet temperature. A reference temperature difference constant ΔT0 is used as a normalized baseline parameter to calibrate the standard temperature difference level under specific operating conditions. The formula for calculating the frosting risk index R1 is as follows: In the formula, RH1 is the relative humidity of the return air (unit: %); T2 is the return air temperature (unit: ℃ or K); T1 is the evaporator outlet temperature (unit: ℃ or K). Reference temperature difference constant (unit: K). The value range thereof is, for example, 10 to 15K, and the specific value is calibrated and determined before delivery according to the design working conditions of the cold-chain compartment. For example, it can be set to 12.5K for a standard refrigerated transport compartment; for a cryogenic transport compartment, it can be set to 14K in consideration of a larger heat transfer temperature difference. The calculated R1 value reflects in real time the dew condensation and frosting trend when air flows through the evaporator. A higher R1 value indicates that a frost layer is more likely to form on the surface of the evaporator.

[0021] Step S2: According to the comparison result between the frosting risk index R1 and the dynamic threshold R2, select to enter one of the following three control states: When R1<R2, enter the steady-state refrigeration state; When R2≤ R1<1.5·R2, enter the pre-frost-suppression state; When R1≥1.5·R2, enter the active defrosting state; The dynamic threshold R2 is calculated in real time by the following formula: R2= R0+ a1· (T3- T0) + b1· (RH1-85%); R0 is the reference threshold, a1 and b1 are correction coefficients, T3 is the ambient temperature, and T0 is the target temperature.

[0022] As an adaptive criterion for judging the frosting risk level, the dynamic threshold R2 is dynamically adjusted with changes in external ambient working conditions and the set target inside the compartment. The reference threshold R0 is an initially set risk threshold of the system, representing the judgment reference for frosting risk under ideal working conditions. The correction coefficients a1 and b1 are respectively used to adjust the influence weight of the ambient temperature deviation and the humidity deviation on the threshold. The ambient temperature T3 refers to the air temperature outside the cold-chain compartment, which is collected by an external temperature sensor; the target temperature T0 is a preset temperature value expected to be maintained inside the compartment. The calculation logic of the dynamic threshold R2 is as follows: In the formula, R0 is the reference threshold; a1 and b1 are correction coefficients; T3 is the ambient temperature (unit: °C); T0 is the target temperature (unit: °C); RH1 is the return air relative humidity (unit: %). The correction coefficients a1, b1 and the reference threshold R0 are, for example, determined through a standard working condition calibration test before the cold-chain compartment leaves the factory and solidified in the controller. For example, a1 can be set to 0.05, and b1 can be set to 0.1; for different types of goods, different parameter combinations can also be configured to meet differentiated temperature control requirements. The dynamic threshold R2 is recalculated in each control cycle, and the control cycle is set to, for example, 500 milliseconds, so as to ensure that the threshold is adaptively adjusted in real time with the ambient working conditions.

[0023] The switching logic of the control states is determined based on the ratio relationship between the frosting risk index R1 and the dynamic threshold R2. When R1<R2, it is determined that the current frosting risk is low, and the system enters a steady-state cooling state to maintain conventional cooling operation so as to keep the temperature inside the compartment stable. When R2≤ R1<1.5·R2, it is determined that there is a potential frosting trend, and the system enters a pre-frost-suppression state to suppress frost layer growth by adjusting operating parameters. When R1≥1.5·R2, it is determined that the frosting risk is high, and the system enters an active defrosting state to start a defrosting procedure to remove the accumulated frost on the surface of the evaporator. This hierarchical control strategy dynamically adjusts the operation mode according to the real-time frosting risk, and avoids energy waste caused by excessive defrosting while ensuring the cooling effect.

[0024] The above technical features work in a coordinated manner to realize precise regulation and control of the low-temperature cold chain environment. By acquiring multi-dimensional parameters such as the evaporator outlet temperature, return air temperature and humidity, and the temperature distribution inside the compartment in real time, the risk index R1 that accurately characterizes the current frosting trend is calculated; combined with the dynamic threshold R2 corrected in real time according to the ambient temperature and target temperature, the system adaptively determines the current frosting risk level; based on the determination result, intelligent switching is performed among the three states of steady-state cooling, pre-frost suppression and active defrosting, so as to achieve a balance between suppressing frosting, maintaining temperature uniformity and reducing energy consumption.

[0025] In an optional embodiment, the method further comprises: the reference temperature difference constant ΔT0 has a value of 10 to 15K, which is calibrated and determined before delivery according to the design working condition of the cold chain compartment; the correction coefficients a1, b1 and the reference threshold R0 are determined through a standard working condition calibration test before the cold chain compartment leaves the factory under the design working condition of the cold chain compartment, and are solidified in the controller; the dynamic threshold R2 is recalculated in each control cycle, and the control cycle is 500 milliseconds, which ensures that the threshold is adaptively adjusted in real time along with the environmental working conditions.

[0026] As a key denominator parameter for calculating the frosting risk index R1, the reference temperature difference constant ΔT0 essentially represents the allowable reference temperature difference between the evaporator surface and the return air. This value directly affects the sensitivity of the frosting model, and is not a simple empirical setting value. Under the design working condition of the cold chain compartment, for example, under the combined condition of specific ambient temperature and target temperature, a series of heat balance tests are carried out to test the heat exchange characteristics of the evaporator under different loads. Multiple sets of sample data of return air relative humidity, return air temperature and evaporator outlet temperature are collected, and the distribution law of temperature difference in the critical state of frosting is analyzed. Finally, an optimal value that can best reflect the thermophysical properties of the specific compartment is determined within the range of 10K to 15K, and stored as a system configuration parameter.

[0027] The correction coefficients a1 and b1, along with the baseline threshold R0, constitute the decision criterion for the dynamic threshold R2. R0 defines the initial frosting risk threshold under standard operating conditions, while a1 and b1 are used to correct for the influence weights of ambient temperature fluctuations and humidity deviations on the frosting process, respectively. The determination of these parameters follows the standard operating condition calibration test specifications: First, a standard transportation environment is simulated in the annular chamber, setting the target temperature T0 and standard humidity level; second, by changing the ambient temperature T3 and the return air relative humidity RH1, the critical R1 values ​​when the system performs frosting or defrosting actions under different operating conditions are recorded; third, using data fitting algorithms such as multiple linear regression or least squares, a linear mapping relationship is established between the critical R1 value and (T3-T0) and (RH1-85%), thereby resolving the specific values ​​of the correction coefficients a1 and b1, as well as the intercept term, i.e., the baseline threshold R0; finally, the verified parameter set is written into the controller's non-volatile memory for solidification, ensuring the stability of the parameters during long-term operation.

[0028] A control cycle of 500 milliseconds defines the time refresh rate of the dynamic threshold R2, characterizing the timeliness requirement of the control logic's response to environmental changes. This cycle value is set by comprehensively considering the thermal inertia of the refrigeration system and the sampling delay of the sensors. It calculates the time constant required for the system to stabilize from a sudden change in operating conditions, selecting a time interval that covers most fluctuations in operating conditions without wasting computational resources. During actual operation, the internally configured timer or scheduling loop triggers a parameter calculation task every 500 milliseconds, reading the latest ambient temperature T3 and return air relative humidity RH1 data. Combined with the R0, a1, and b1 parameters embedded in the controller, the dynamic threshold R2 is updated in real time. Through this high-frequency calculation and update mechanism, the system can capture rapid fluctuations in ambient temperature or humidity changes caused by cargo respiration, ensuring that the frost risk assessment benchmark remains synchronized with the current physical thermal environment, avoiding control lag or misjudgment caused by using a fixed threshold.

[0029] In one possible implementation, the method further includes S211: In steady-state refrigeration, the compressor frequency is PID closed-loop regulated according to the target temperature deviation, with an adjustment period of 1 second, a proportional gain coefficient of 0.8, an integral time of 120 seconds, and a derivative time of 15 seconds.

[0030] Once the system enters steady-state refrigeration, it initiates precise control logic for the variable frequency compressor to maintain dynamic temperature balance within the cold chain compartment. This control logic employs a continuous adjustment mechanism based on a Proportional-Integral-Derivative (PID) algorithm, replacing the traditional on / off control mode. The difference between the target temperature and the actual temperature inside the compartment is used as the core input signal. The proportional, integral, and derivative components of this deviation are calculated, and then a control command for the compressor's operating frequency is synthesized.

[0031] The adjustment cycle is set to 1 second, meaning the controller collects temperature deviation data and updates the output frequency every second. This shorter sampling and adjustment interval ensures the system responds quickly to changes in heat load, effectively suppressing large temperature fluctuations caused by control lag.

[0032] At the parameter configuration level, the proportional gain coefficient is set to 0.8 to linearly map the temperature deviation into a control variable. This value aims to balance the system's response speed and stability, preventing excessive gain from causing system oscillations and avoiding insufficient gain from causing sluggish response. The integral time is set to 120 seconds to eliminate steady-state error through the accumulation of historical deviations, ensuring that the chamber temperature eventually converges to the target setpoint without steady-state error. The derivative time is set to 15 seconds to implement anticipatory adjustment based on the rate of change of the deviation, suppressing overshoot when the temperature approaches the target value and enhancing the system's damping characteristics.

[0033] Through PID closed-loop regulation using the aforementioned specific parameter combination, the system can automatically correct the compressor output power based on real-time heat load fluctuations during the steady-state refrigeration phase, thereby achieving high-precision temperature maintenance and enhancing the quality assurance capability of goods during cold chain transportation.

[0034] The method also includes S212: In steady-state refrigeration, the opening of the electronic expansion valve tracks the superheat at the evaporator outlet. The target value of the superheat is 5.5K, and the allowable fluctuation range is ±0.5K. The adjustment step of the opening of the electronic expansion valve is 1.5% each time, and the opening of each air outlet is uniformly set to 100% to achieve balanced air supply.

[0035] After entering steady-state refrigeration, the system executes a closed-loop control strategy with the evaporator outlet superheat as the controlled variable, aiming to maintain the evaporator's optimal heat exchange efficiency. Evaporator outlet superheat is defined as the difference between the actual temperature of the refrigerant at the evaporator outlet and the saturation temperature at the corresponding pressure. The real-time superheat is calculated by acquiring the evaporator outlet temperature T1 in real time and combining it with the saturation temperature corresponding to the current operating pressure.

[0036] The target superheat value is set at 5.5K. This value comprehensively considers the heat transfer characteristics of the refrigerant and the safety of system operation: on the one hand, it prevents the risk of liquid slugging caused by incomplete refrigerant evaporation entering the compressor; on the other hand, it avoids excessive superheat leading to a reduction in the effective heat exchange area utilization of the evaporator. Setting an allowable fluctuation range of ±0.5K, that is, tolerating small fluctuations in superheat within the range of 5.0K to 6.0K, can effectively suppress system oscillations caused by frequent adjustments and improve control stability.

[0037] For the adjustment of the electronic expansion valve opening, a fine adjustment is made in fixed steps of 1.5% each time to ensure smooth opening changes. When the detected actual superheat is below 5.0K, it is determined that the refrigerant charge in the evaporator is too high, and the electronic expansion valve is controlled to decrease its opening in 1.5% steps, thereby reducing the refrigerant flow. When the actual superheat is above 6.0K, it is determined that the refrigerant supply is insufficient, and the electronic expansion valve is controlled to increase its opening in 1.5% steps, thereby increasing the refrigerant flow. This gradual approach adjustment mechanism can stably maintain the superheat within the target range, ensuring the efficient and safe operation of the refrigeration cycle.

[0038] Meanwhile, the opening of each air outlet is uniformly controlled at 100% to achieve balanced airflow. In the multi-outlet air supply mechanism, each damper actuator is driven to the fully open state, maximizing the air supply cross-sectional area. This configuration allows the cold air, cooled by the evaporator, to be delivered into the cold chain compartment with minimal air resistance and maximum flow rate. The forced airflow in the fully open state accelerates the circulation of air inside the compartment, causing the cold air to quickly diffuse to every corner, effectively eliminating localized temperature anomalies caused by dead airflow. By maintaining the consistency of the opening of each air outlet, the uniformity of airflow distribution is ensured, making the vertical temperature distribution inside the compartment more uniform, meeting the stringent requirements of cold chain transportation for temperature field uniformity.

[0039] The aforementioned electronic expansion valve's precise closed-loop control of superheat, combined with the fully open and balanced air supply strategy of the air outlet, enables the system to significantly improve the evaporator's energy efficiency ratio and maintain the dynamic balance of the temperature field inside the compartment during the steady-state refrigeration phase, while ensuring safe and stable operation, thus providing a constant and reliable low-temperature storage environment for goods.

[0040] like Figure 2The diagram shows a flowchart illustrating the gradual reduction of the electronic expansion valve opening in the pre-frost suppression state and the additional or retrograde adjustment based on wall temperature changes in a precise control method for cold chain low-temperature environments provided in this application embodiment. The method further includes: in the pre-frost suppression state, the electronic expansion valve opening is gradually reduced at a rate of 3% per second within 3 seconds of entering the pre-frost suppression state, with a total reduction of 8% to 14% of the current opening; after the reduction, the evaporator wall temperature change is monitored; if the wall temperature increase is less than 0.3K, an additional 2% reduction is added in the next control cycle; if the wall temperature increase exceeds 0.8K, a 1.5% retrograde adjustment is performed in the next control cycle.

[0041] In the pre-frost suppression state, the opening of the electronic expansion valve is gradually reduced at a rate of 3% per second within 3 seconds after entering the pre-frost suppression state, with a total reduction of 8% to 14% of the current opening.

[0042] When the system determines that it has entered a pre-defrost state based on the frosting risk index, it immediately initiates an intervention procedure on the opening of the electronic expansion valve. This intervention aims to gradually reduce the refrigerant flow into the evaporator, thereby suppressing the frosting rate on the evaporator surface without interrupting the refrigeration cycle. Unlike existing technologies that may cause liquid slugging or low-pressure alarms by directly and drastically closing the valve, this embodiment adopts a dynamic execution strategy of gradually reducing the valve opening.

[0043] Specifically, the adjustment process is limited to the first 3-second time window after entering the pre-defrost state, and the rate of reduction is strictly controlled at 3% per second to ensure the smoothness of the adjustment. The total reduction is set to 8% to 14% of the current opening, a range determined based on the heat load characteristics of a typical cold chain compartment evaporator near the frosting critical point. This range effectively reduces the heat exchange temperature difference on the evaporator surface, delaying moisture condensation, while maintaining sufficient refrigerant flow to meet the basic cooling requirements of the compartment and avoiding temperature fluctuations caused by a sudden decrease in flow.

[0044] After the adjustment is made, monitor the change in evaporator wall temperature. If the increase in wall temperature does not reach 0.3K, then make an additional 2% adjustment in the next control cycle.

[0045] After completing the initial reduction action, the system transitions to a closed-loop monitoring phase to assess the adjustment effect. Evaporator wall temperature, a key physical quantity reflecting the internal phase change heat balance of the evaporator, directly characterizes the matching degree between the refrigerant supply and the heat load. Temperature sensors deployed on the evaporator coil walls collect wall temperature data in real time and calculate its increase relative to the initial reduction. If the monitored wall temperature increase is less than 0.3K, it indicates that although the refrigerant supply has been reduced, the temperature rise on the evaporator surface is insufficient to significantly alter the thermodynamic conditions for frosting, or that the external heat load remains high, and the current reduction in opening is too weak to create an effective defrosting barrier. Therefore, in the next control cycle, an additional reduction strategy is implemented, further reducing the opening by 2% from the existing level. This secondary correction mechanism based on temperature feedback can adapt to fluctuations in operating conditions caused by different cargo heat loads and door opening frequencies, ensuring the effectiveness of the defrosting measures.

[0046] If the wall temperature rises by more than 0.8K, it will be reduced by 1.5% in the next control cycle.

[0047] If the monitored wall temperature increase exceeds 0.8K, it indicates that the initial downward adjustment resulted in insufficient refrigerant flow, causing excessive refrigerant evaporation in the evaporator, and even localized dry-sun exposure. Excessively low evaporation pressure may pose a potential threat to the compressor's operational stability. To prevent a significant drop in the system's energy efficiency ratio due to excessive throttling, or to trigger compressor protection shutdown due to excessively low suction pressure, a callback mechanism is introduced. In the next control cycle, the electronic expansion valve opening is adjusted back by 1.5%, appropriately increasing the valve opening to increase refrigerant supply. This callback action aims to bring the wall temperature back to the normal fluctuation range, eliminating the system operational risks caused by excessive throttling. By setting two clearly defined physical thresholds of 0.3K and 0.8K, a precise quantitative balance is established between defrosting effect and system stability.

[0048] Through the above steps, the opening adjustment of the electronic expansion valve no longer relies on a simple open-loop timing strategy, but instead forms a dual-layer control architecture of coarse adjustment + fine adjustment. The coarse adjustment stage responds quickly to the risk of frosting through preset rates and amplitudes, while the fine adjustment stage performs refined corrections based on real-time feedback from the evaporator wall temperature, a core state variable. This synergistic effect allows the cold chain compartment to maintain optimal refrigerant flow balance under pre-frost suppression conditions, effectively delaying frost growth and ensuring the safe and stable operation of the refrigeration system.

[0049] like Figure 3 The diagram shows a flowchart illustrating an embodiment of this application for adjusting the airflow ratio between the top and bottom air outlets based on the vertical temperature difference within the compartment. The method further includes step S222: In the pre-frost suppression state, adjusting the airflow ratio between the top and bottom air outlets according to the vertical temperature difference ΔT1 within the compartment: when... At that time, the top air outlet opening increases to 70%, and the bottom air outlet opening decreases to 30%, with the adjustment completed within 2 seconds; when At that time, the opening of both the top and bottom air outlets returned to 50%, ensuring balanced airflow.

[0050] Step S301: When At that time, the opening of the top air outlet increases to 70%, and the opening of the bottom air outlet decreases to 30%, with the adjustment completed within 2 seconds.

[0051] Vertical temperature difference inside the compartment This data is used to characterize the uniformity of temperature distribution in the vertical direction inside a cold chain container. The value is typically defined as the difference between the temperature at the top and bottom of the measuring point inside the container. This data can be derived from the vertical temperature distribution inside the container obtained in the preceding steps. This is obtained by differential calculation of temperature data at a specific height (such as the top and bottom stacking areas of goods). If the calculated... Greater than If this is the case, it is determined that there is a significant air thermal stratification phenomenon inside the compartment, resulting in inconsistent storage environments for goods in the upper and lower areas.

[0052] To address this operating condition, the airflow distribution is adjusted via a multi-outlet air supply mechanism, increasing the opening of the top air outlet to 70% while decreasing the opening of the bottom air outlet to 30%. This differential opening adjustment aims to alter the pressure distribution and velocity vector of the airflow field, forcing more airflow from the high-pressure area at the top to the low-pressure area at the bottom, thereby enhancing the vertical air mixing capacity. This adjustment is configured to complete within 2 seconds; this rapid response effectively prevents further deterioration of temperature stratification due to adjustment lag, while ensuring that airflow organization optimization is completed within a short time window during the pre-frost suppression phase.

[0053] Step S302: When At that time, the opening of both the top and bottom air outlets returned to 50%, ensuring balanced airflow.

[0054] If the vertical temperature difference inside the chamber is monitored Less than or equal to This indicates that the vertical temperature distribution within the compartment has returned to the preset uniformity standard range, and there is no longer a significant temperature gradient. In this state, to reduce unnecessary energy consumption of the blower and minimize cargo dryness caused by localized high wind speeds, the opening of both the top and bottom air vents is restored to 50%, re-entering the balanced air supply mode. In balanced air supply mode, the multi-vent air supply mechanism remains symmetrically open, creating a uniform airflow coverage field within the compartment and ensuring that the temperature in each area is dynamically balanced. This automatic switching mechanism achieves a smooth transition from strong intervention to stable maintenance, ensuring both the control strength under extreme temperature differences and maintaining operational economy under normal conditions.

[0055] By adjusting the dynamic airflow ratio based on the vertical temperature difference within the compartment, an adaptive airflow organization mechanism is established in the pre-frost suppression state. This mechanism responds in real time to the temperature stratification state and actively disrupts the stratification structure of hot and cold air caused by gravity by differentially adjusting the opening of the air outlets. This transforms the potentially abnormal distribution of cold air at the top and hot air at the bottom into a uniform temperature field, thereby ensuring the consistency and safety of the storage environment for goods within the cold chain compartment.

[0056] The method also includes S231: In active defrosting mode, immediately stop the compressor, close the electronic expansion valve to 0% opening, turn on the defrosting heating device, start the defrosting heating device at 80% of rated power, and after 30 seconds, increase to 100% of rated power.

[0057] Upon entering active defrosting mode, the compressor is stopped first, quickly cutting off the refrigerant circulation. This operation aims to prevent refrigerant from continuing to flow in the low-temperature lines during defrosting heating, thus preventing liquid slugging or excessively high condensing pressure from affecting the safe isolation of the refrigeration system. Simultaneously, the electronic expansion valve is adjusted to 0%, completely blocking the refrigerant supply path to the evaporator, ensuring that no new low-temperature refrigerant enters the evaporator, thereby creating an independent thermodynamic environment for defrosting heating.

[0058] After the refrigeration cycle is cut off, the defrosting heating device is activated, using electrical energy converted into heat energy to directly melt the frost on the evaporator surface. To reduce the thermal shock stress on the evaporator metal pipes during the initial defrosting start-up, the defrosting heating device adopts a staged start-up strategy: in the initial stage, it heats at 80% of the rated power, allowing the evaporator temperature to rise gradually, promoting the slow release of thermal expansion in the metal pipes, and avoiding structural damage or weld cracking due to drastic temperature changes.

[0059] After a 30-second preheating period, the defrosting heating device automatically increases its output power to 100% of its rated power, entering the full-power defrosting stage. This strategy maximizes heating efficiency while ensuring equipment safety, effectively shortening the total defrosting time, thereby reducing temperature fluctuations inside the cold chain compartment and maintaining the stability of the goods storage environment.

[0060] like Figure 4 The diagram shows a flowchart illustrating how to terminate defrosting and restore steady-state refrigeration based on temperature duration or total duration during active defrosting, according to an embodiment of this application. The method further includes step S232: In the active defrosting state, the defrosting termination condition is the evaporator outlet temperature. And the duration exceeds 30 seconds, or the total defrosting time exceeds the preset maximum defrosting time of 15 minutes; after defrosting is completed, turn off the defrosting heating device, wait 30 seconds and then restart the compressor, and restore the opening of the electronic expansion valve to the opening before entering the active defrosting state, and then return to the steady state of cooling.

[0061] Step S401: In active defrosting mode, the defrosting termination condition is the evaporator outlet temperature. And the duration exceeds 30 seconds, or the total creaming time exceeds the preset maximum creaming time of 15 minutes.

[0062] During active defrosting, to avoid decreased cooling efficiency due to incomplete defrosting, or energy waste and drastic temperature fluctuations inside the cabinet due to overheating, the system has set strict defrosting termination conditions. These conditions are a composite criterion formed by the evaporator outlet temperature and the total defrosting time, creating an OR-logic relationship. The preset maximum defrosting time of 15 minutes is a safety limit determined based on the typical heat load characteristics of a cold chain compartment and the power configuration of the defrosting heating device, aiming to prevent the heating process from continuing indefinitely due to sensor malfunctions or abnormal operating conditions.

[0063] When the active defrosting time reaches the upper limit, the system forcibly terminates the defrosting process regardless of whether the actual frost on the evaporator surface has been completely removed. This is to protect the equipment and prevent damage to the goods inside the container due to prolonged high temperatures. For temperature-based criteria, the system monitors the evaporator outlet temperature T1 in real time. This temperature directly reflects the heat exchange status and frost residue on the evaporator surface. When T1 reaches or exceeds 2°C, it indicates that the evaporator surface temperature has risen above the freezing point, and the attached frost layer begins to melt and fall off.

[0064] To ensure the thoroughness of the defrosting process and prevent misjudgments caused by brief temperature fluctuations, a continuous confirmation mechanism based on time was introduced, requiring that the state of T1≥2℃ must be maintained continuously for more than 30 seconds. This dual confirmation, combining temperature threshold and duration, effectively filters out instantaneous temperature rise signals caused by intermittent heater operation or cold air recirculation, ensuring that the defrosting process only stops after the evaporator surface has truly returned to its frost-free heat exchange capacity.

[0065] This processing method differs from existing single-time control defrosting technology. Through real-time temperature feedback and time window filtering, it achieves precise capture of the defrosting end point, maximizing energy utilization efficiency while ensuring the defrosting effect.

[0066] After defrosting is complete, the defrosting heating device is turned off. When any of the above defrosting termination conditions are met, the system immediately controls the defrosting heating device to stop operating.

[0067] This action aims to cut off the active heat source, terminating the heating process for the evaporator and the air flowing through it, and preventing the internal temperature from continuing to rise after defrosting. The operation to shut down the defrosting heating device is achieved by the main controller outputting a shutdown command to the heating device's drive circuit. At this time, the system no longer provides additional heat input to the evaporator side. After this action is completed, the system enters a brief shutdown balancing phase, creating a safe pressure and temperature environment for the subsequent restart of the refrigeration system, avoiding compressor damage caused by pressurized startup or thermal stress shock.

[0068] Restart the compressor after 30 seconds. After the defrosting heater is turned off, the system does not immediately resume the refrigeration cycle, but instead forces a static waiting period of 30 seconds. This waiting time is designed based on the physical characteristics of the refrigeration system: at the instant the defrosting heater stops, there may be high-pressure refrigerant gas or liquid refrigerant remaining in the evaporator and suction line, and the internal pressure distribution of the system has not yet reached equilibrium.

[0069] Starting the compressor immediately at this point can easily trigger liquid slugging, potentially causing compressor valve plate breakage or crankshaft connecting rod damage. Simultaneously, high back pressure startup can lead to excessive compressor starting current, increasing the risk of grid impact and motor winding temperature rise. By setting a 30-second waiting period, the high and low pressure sides of the system are allowed to naturally approach equilibrium, and the refrigerant remaining in the pipeline is allowed to fully return or vaporize, thus ensuring smooth compressor startup under light or no-load conditions. This 30-second duration is based on empirical values ​​for gas return balance in conventional refrigeration systems. For cold chain compartments of different volumes or refrigerant types, this value can be adjusted experimentally within a range of 20 to 45 seconds.

[0070] This static waiting mechanism effectively avoids the operational risks of equipment after defrosting by using a low-cost physical delay, thereby improving the startup reliability and service life of the refrigeration system.

[0071] The electronic expansion valve opening is then restored to its pre-defrosting state. During compressor shutdown and waiting, the system synchronously performs this reset operation. The electronic expansion valve is a key throttling element in the refrigeration system, regulating refrigerant flow; its opening directly determines the amount of refrigerant supplied to the evaporator. Before entering active defrosting, the system is typically in a steady-state refrigeration state or a pre-defrost state. At this time, the electronic expansion valve opening has been adjusted to the optimal value matching the current heat load; this historical opening record reflects the system's stable operating state before defrosting.

[0072] During defrosting, the electronic expansion valve is typically closed (i.e., its opening is set to 0%) to facilitate defrosting or protect the compressor. After defrosting, blindly restoring the electronic expansion valve to its fixed initial opening often fails to match the actual operating conditions at the moment of restart, potentially leading to excessively low suction pressure or insufficient liquid supply, thus prolonging the system's recovery time to normal cooling. Therefore, a strategy of restoring the historical state is adopted, resetting the electronic expansion valve's opening to the recorded value before entering active defrosting mode. This restoration process is achieved by the controller reading the historical opening variable A1 stored in memory and sending it as a setpoint to the stepper motor driving the electronic expansion valve.

[0073] By directly reusing the opening parameters that have been verified as reasonable before defrosting, the compressor can obtain a refrigerant flow rate close to that before defrosting at the moment of restart, thereby significantly shortening the transition time of the system from shutdown to stable cooling conditions and reducing temperature fluctuations caused by adjustment oscillations.

[0074] The system then returns to steady-state refrigeration. After the compressor restarts and the electronic expansion valve opening is restored, the control system switches from active defrosting to steady-state refrigeration. In steady-state refrigeration, the system regains control over precise temperature control inside the compartment. Based on the target temperature deviation, it performs PID closed-loop regulation of the compressor frequency and fine-tunes the electronic expansion valve by tracking the evaporator outlet superheat, ensuring the internal environment of the cold chain compartment quickly returns to the set low-temperature storage conditions.

[0075] Through the orderly connection of the above steps, a complete control loop of defrosting execution, condition determination, safe shutdown, and smooth restart is achieved, ensuring a smooth transition between the defrosting process and the refrigeration process.

[0076] The aforementioned technical features, through synergistic action, solve the technical problems of difficulty in accurately controlling the end of defrosting and instability during system restart. Based on the dual criteria of an evaporator outlet temperature T1 greater than or equal to 2 degrees Celsius for 30 seconds, coupled with a 15-minute maximum defrosting time limit, it ensures that the defrosting process neither terminates prematurely nor is extended indefinitely, thus balancing energy efficiency and safety while guaranteeing thorough defrosting.

[0077] The 30-second static waiting period after shutting down the defrosting heater provides necessary physical buffer time for the refrigeration system pressure to balance, eliminating the risks of liquid slugging and high-pressure startup, and protecting the compressor's core components. The electronic expansion valve opening returns to its state before entering active defrosting mode, using historical operating parameters as a restart benchmark. This ensures that the refrigeration cycle achieves ideal flow matching instantly upon recovery, significantly shortening the adjustment time required for operational recovery.

[0078] Through the close coordination of these steps, this application realizes a safe, energy-saving and rapid defrosting control strategy, which effectively improves the overall operational stability of the cold chain low-temperature environment control system and the ability to ensure the quality of goods.

[0079] The method also includes S233: During the active defrosting state, the blower operates in reverse mode, the reverse air speed is 30% to 60% of the normal air supply speed, the reverse start delay is 5 seconds after the start of defrosting, the reverse duration is 80% of the total defrosting time, and the forward air supply is restored 30 seconds before the end of defrosting to exhaust residual heat.

[0080] The reverse fan mode, as a dynamic airflow control strategy, aims to change the direction of airflow during the defrosting process. Compared to the problems caused by the blower maintaining forward operation or stopping during traditional active defrosting, such as localized heat accumulation, uneven defrosting, and easy re-condensation of residual hot and humid gas, this mode forces the airflow to flow in reverse, guiding the heated air into the gaps between the evaporator fins and the bottom frost area. This effectively eliminates the dead zones formed by unidirectional airflow, thereby accelerating the overall melting of the frost layer.

[0081] For the timing and wind speed parameters of reverse operation, a 5-second delay is set after defrosting begins as the reverse start delay. This delay period corresponds to the preheating stage of the defrosting heating device, during which the heating device gradually increases the ambient air temperature, and the airflow does not yet have an efficient heat-carrying capacity. By reserving a 5-second delay, a temperature gradient is pre-established in the local environment around the evaporator, preventing cold airflow from directly impacting the heating element and causing heat loss.

[0082] After the delay ends, the blower operates at 30% to 60% of the normal supply air velocity as the reverse air velocity. This velocity range is selected to balance the intensity of airflow disturbance with heat transfer efficiency. For example, if the normal supply air velocity is 10 m / s, the reverse air velocity can be set to 3 to 6 m / s. This moderate-intensity reverse airflow ensures that hot air fully penetrates the frost layer while preventing airflow short-circuiting due to excessive velocity, guaranteeing sufficient residence time for heat on the evaporator surface for efficient heat exchange.

[0083] The reverse operation duration is set to 80% of the total defrosting time, establishing reverse airflow as the dominant phase in the defrosting cycle to enhance heat transfer. During this phase, the system continuously utilizes reverse airflow to quickly remove stubborn frost. For example, with a preset maximum defrosting time of 15 minutes, the blower will continuously run in reverse for 12 minutes. Once this duration threshold is reached, it indicates that the frost layer on the evaporator surface has largely melted, and the system then enters the defrosting completion phase, performing environmental condition restoration operations.

[0084] In the last 30 seconds before defrosting ends, the blower switches back to forward rotation mode. This uses high-speed forward airflow to quickly expel the hot and humid gas accumulated on the evaporator surface and in the air ducts, preventing the residual hot and humid gas from condensing into water or ice upon contact with the low-temperature evaporator surface when defrosting ends and the refrigeration system restarts.

[0085] This process effectively reduces the risk of immediate frost formation after defrosting, shortens the time it takes for the internal temperature of the compartment to recover to the target refrigeration temperature, and ensures temperature stability during cold chain transportation.

[0086] like Figure 5 The diagram shows a flowchart illustrating how to correct a dynamic threshold and forcibly exit or pause the active defrosting state when a door opening event is detected, according to an embodiment of this application. The method further includes: when a door opening event is detected, correcting the dynamic threshold based on the cumulative door opening duration t0 and the number of personnel entering and exiting n1. Among them, t1 is the control cycle, and it is forced to exit the active defrosting state during the door opening period. If defrosting is in progress, it will be paused and switched to the pre-defrosting state until it is closed and resumed. During the defrosting pause, the defrosting heating device stops working, the compressor remains in the stopped state, and the blower resumes positive low-speed air supply with a wind speed of 20% of the normal air supply wind speed.

[0087] Door opening is a key trigger for identifying heat and humidity interaction between the cold chain container and the external environment. During cold chain logistics transportation or refrigerated storage operations, door opening causes high humidity and high temperature air from outside to rapidly enter the container, resulting in instantaneous and drastic fluctuations in the return air humidity sensor reading RH1 and the return air temperature T2.

[0088] If the dynamic threshold under normal operating conditions is still used to determine the risk of frost formation, it is very easy to misjudge this parameter jump caused by human activity as a high risk of frost formation, thus erroneously triggering the active defrosting state. Therefore, the door status is monitored in real time by a door magnetic switch sensor or an infrared beam sensor. Once a door opening signal is detected, special control logic for door opening interference is activated.

[0089] In response to the acquisition of the door opening signal, the dynamic threshold is corrected based on the cumulative door opening duration t0 and the number of personnel entering and exiting n1. This correction process aims to quantify the impact of external humid and hot air intrusion on the interior environment and dynamically adjust the frost determination criteria. The cumulative door opening duration t0 represents the mixing and exchange time window between external air and interior air; the longer the time, the greater the total intrusive moisture load. The number of personnel entering and exiting n1 represents the frequency of instantaneous moisture disturbance brought in with the door opening action.

[0090] The above modified formula constructs a linear decay model for the intensity of human activity, used to reduce the basic dynamic threshold R². The formula is formally expressed as: In the formula, R3 represents the corrected dynamic threshold, which is the threshold value for determining whether the system enters a high-frosting-risk state under the current door opening interference level; t0 represents the cumulative door opening duration from the current door opening time, usually in seconds (s); t1 is the control period, which is related to the system's control sampling frequency, for example, it can be set to 500 milliseconds to normalize the time and eliminate the influence of dimensions; n1 represents the number of people entering and exiting during the detected door opening time period.

[0091] The coefficients 0.2 and 0.1 are the time weighting factor and the frequency weighting factor, respectively, used to perform weighted balancing based on the contribution of different physical quantities. The constant 5 in the denominator is the normalization constant, used to convert the number of entries and exits into dimensionless relative values. The R3 value calculated by this formula is usually smaller than the original R2 value, thus effectively increasing the difficulty of triggering active defrosting during door opening and preventing misjudgment.

[0092] Based on the modified dynamic threshold R3, a control strategy is implemented to force the exit from active defrosting mode during door opening. During this special period, regardless of the level of the frost risk index R1 calculated in the aforementioned steps, the system logic disables the decision branch used to enter active defrosting mode (i.e., R1≥1.5×R2) and prohibits the activation of the defrosting heating device.

[0093] This operation avoids ineffective and energy-intensive defrosting heating when the door is open and a large amount of heat is lost. It also prevents the high-temperature airflow generated during defrosting from leaking directly to the outside or affecting refrigerated goods if it is not circulated. If the system is in the active defrosting heating phase when a door opening event is detected, the current defrosting process is immediately interrupted, and the control mode is switched from active defrosting to pre-defrosting.

[0094] During the defrosting pause, all actuators are controlled to enter a specific maintenance state: the defrosting heating device stops working, the compressor remains off, and the blower resumes forward low-speed airflow, with the airflow speed set to 20% of the normal airflow speed. The defrosting heating device stops working to comply with the command to forcibly exit the active defrosting state, completely cutting off the heat source and avoiding energy waste and potential safety risks.

[0095] The compressor is kept off because the cooling load is extremely unstable and there is a risk of negative pressure backflow when the door is open. Shutting it off protects the compressor and prevents it from drawing in overheated gas mixture. The fan resumes positive low-speed airflow to maintain basic airflow within the compartment and prevent dead zones or hot spots. Although the fan speed is reduced to 20% of the normal airflow speed (e.g., 20% of the rated speed), this micro-air circulation can still slowly circulate the air within the compartment across the sensor surface without exacerbating the loss of cooling capacity. This ensures the real-time and accurate monitoring of parameters and creates a stable airflow environment for subsequent resumption of cooling or defrosting operations.

[0096] By detecting door opening events and calculating the correction threshold R3, the system can distinguish between the actual frost accumulation trend and the instantaneous fluctuations in environmental parameters caused by door opening and closing. The mechanism for forcibly exiting or pausing active defrosting, combined with the energy-saving standby configuration of each actuator during the pause, ensures that the refrigerated container maintains a stable thermal environment even during frequent loading and unloading operations. This avoids temperature fluctuations and energy losses caused by ineffective defrosting operations, ensuring the economy of cold chain transportation and the quality of goods.

[0097] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for precise control of low-temperature environment in cold chain, applicable to cold chain compartments equipped with variable frequency compressors, electronic expansion valves, evaporators, multi-outlet air supply mechanisms, return air humidity sensors, evaporator temperature sensors, and compartment temperature sensors, characterized in that, Includes the following steps: S1: Obtain real-time operating parameters, including: evaporator outlet temperature T1, return air relative humidity RH1, return air temperature T2, vertical temperature distribution inside the chamber T(z,t) and electronic expansion valve opening A1; The frost risk index R1 is calculated based on the difference between the return air relative humidity RH1 and the evaporator outlet temperature T1: R1 = RH1 × (T2 - T1) / ΔT0; Where ΔT0 is the reference temperature difference constant; S2: Based on the comparison between the frost risk index R1 and the dynamic threshold R2, select one of the following three control states: When R1 < R2, the system enters a steady-state cooling state. when At this time, it enters the pre-frost suppression state; When R1 ≥ 1.5·R2, it enters the active defrosting state; The dynamic threshold R2 is calculated in real time by the following formula: R0 is the baseline threshold, a1 and b1 are correction coefficients, T3 is the ambient temperature, and T0 is the target temperature.

2. The method according to claim 1, characterized in that, The reference temperature difference constant ΔT0 is set to 10~15K and is determined by calibration before leaving the factory according to the design conditions of the cold chain compartment. The correction coefficients a1, b1 and the reference threshold R0 are determined by standard operating condition calibration tests before leaving the cold chain compartment and are fixed in the controller. The dynamic threshold R2 is recalculated in each control cycle, and the control cycle is 500 milliseconds to ensure that the threshold is adaptively adjusted in real time according to the environmental conditions.

3. The method according to claim 1, characterized in that, It also includes S211: In the steady-state refrigeration state, the compressor frequency is PID closed-loop regulated according to the target temperature deviation, with an adjustment period of 1 second, a proportional gain coefficient of 0.8, an integral time of 120 seconds, and a derivative time of 15 seconds.

4. The method according to claim 1, characterized in that, It also includes S212: In the steady-state refrigeration state, the opening degree of the electronic expansion valve tracks the superheat of the evaporator outlet. The target value of the superheat is 5.5K, and the allowable fluctuation range is ±0.5K. The adjustment step of the opening degree of the electronic expansion valve is 1.5% each time. The opening degree of each air outlet is uniformly set to 100% to achieve balanced air supply.

5. The method according to claim 1, characterized in that, It also includes S221: In the pre-defrost state, the opening of the electronic expansion valve is gradually reduced at a rate of 3% per second within 3 seconds after entering the pre-defrost state, with a total reduction of 8% to 14% of the current opening; after the reduction, the evaporator wall temperature change is monitored. If the wall temperature increase does not reach 0.3K, an additional 2% reduction is added in the next control cycle; if the wall temperature increase exceeds 0.8K, a 1.5% adjustment is made in the next control cycle.

6. The method according to claim 1, characterized in that, It also includes S222: In the pre-frost suppression state, the air volume ratio of the top and bottom air outlets is adjusted according to the vertical temperature difference ΔT1 in the chamber: when ΔT1 > 1.5℃, the opening of the top air outlet increases to 70% and the opening of the bottom air outlet decreases to 30%, and the adjustment is completed within 2 seconds; when ΔT1 ≤ 1.5℃, the opening of both the top and bottom air outlets is restored to 50%, and the air is supplied evenly.

7. The method according to claim 1, characterized in that, It also includes S231: In the active defrosting state, the compressor is stopped immediately, the electronic expansion valve is closed to 0% opening, the defrosting heating device is turned on, the defrosting heating device starts at 80% of the rated power, and after 30 seconds it rises to 100% of the rated power.

8. The method according to claim 1, characterized in that, It also includes S232: In the active defrosting state, the defrosting termination condition is the evaporator outlet temperature. And the duration exceeds 30 seconds, or the total defrosting time exceeds the preset maximum defrosting time of 15 minutes; after defrosting is completed, turn off the defrosting heating device, wait 30 seconds and then restart the compressor, and restore the opening of the electronic expansion valve to the opening before entering the active defrosting state, and then return to the steady state of cooling.

9. The method according to claim 1, characterized in that, It also includes S233: During the active defrosting state, the blower operates in reverse mode, the reverse wind speed is 30% to 60% of the normal wind speed, the reverse start delay is 5 seconds after the start of defrosting, the reverse duration is 80% of the total defrosting time, and the forward air supply is restored 30 seconds before the end of defrosting to exhaust residual heat.

10. The method according to claim 1, characterized in that, When a door opening event is detected, the dynamic threshold is adjusted based on the cumulative door opening duration t0 and the number of people entering and exiting n1: Among them, t1 is the control cycle, and it is forced to exit the active defrosting state during the door opening period. If defrosting is in progress, it will be paused and switched to the pre-defrosting state until it is closed and resumed. During the defrosting pause, the defrosting heating device stops working, the compressor remains in the stopped state, and the blower resumes positive low-speed air supply with a wind speed of 20% of the normal air supply wind speed.

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